blob: 188d983821384e2f7c5e9b40218fb9e053935785 [file] [log] [blame]
// Copyright 2018 The Fuchsia Authors
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT
#include "kernel/scheduler.h"
#include <assert.h>
#include <debug.h>
#include <inttypes.h>
#include <lib/counters.h>
#include <lib/ktrace.h>
#include <lib/zircon-internal/macros.h>
#include <platform.h>
#include <stdio.h>
#include <string.h>
#include <trace.h>
#include <zircon/errors.h>
#include <zircon/listnode.h>
#include <zircon/types.h>
#include <new>
#include <arch/ops.h>
#include <ffl/string.h>
#include <kernel/cpu.h>
#include <kernel/lockdep.h>
#include <kernel/mp.h>
#include <kernel/percpu.h>
#include <kernel/scheduler.h>
#include <kernel/scheduler_internal.h>
#include <kernel/scheduler_state.h>
#include <kernel/thread.h>
#include <kernel/thread_lock.h>
#include <ktl/algorithm.h>
#include <ktl/forward.h>
#include <ktl/move.h>
#include <ktl/pair.h>
#include <object/thread_dispatcher.h>
#include <vm/vm.h>
using ffl::FromRatio;
using ffl::Round;
// Determines which subset of tracers are enabled when detailed tracing is
// enabled. When queue tracing is enabled the minimum trace level is
// KTRACE_COMMON.
#define LOCAL_KTRACE_LEVEL \
(SCHEDULER_TRACING_LEVEL == 0 && SCHEDULER_QUEUE_TRACING_ENABLED ? KTRACE_COMMON \
: SCHEDULER_TRACING_LEVEL)
// The tracing levels used in this compilation unit.
#define KTRACE_COMMON 1
#define KTRACE_FLOW 2
#define KTRACE_COUNTER 3
#define KTRACE_DETAILED 4
// Evaluates to true if tracing is enabled for the given level.
#define LOCAL_KTRACE_LEVEL_ENABLED(level) ((LOCAL_KTRACE_LEVEL) >= (level))
#define LOCAL_KTRACE(level, string, args...) \
ktrace_probe(LocalTrace<LOCAL_KTRACE_LEVEL_ENABLED(level)>, TraceContext::Cpu, \
KTRACE_STRING_REF(string), ##args)
#define LOCAL_KTRACE_FLOW_BEGIN(level, string, flow_id, args...) \
ktrace_flow_begin(LocalTrace<LOCAL_KTRACE_LEVEL_ENABLED(level)>, TraceContext::Cpu, \
KTRACE_GRP_SCHEDULER, KTRACE_STRING_REF(string), flow_id, ##args)
#define LOCAL_KTRACE_FLOW_END(level, string, flow_id, args...) \
ktrace_flow_end(LocalTrace<LOCAL_KTRACE_LEVEL_ENABLED(level)>, TraceContext::Cpu, \
KTRACE_GRP_SCHEDULER, KTRACE_STRING_REF(string), flow_id, ##args)
#define LOCAL_KTRACE_FLOW_STEP(level, string, flow_id, args...) \
ktrace_flow_step(LocalTrace<LOCAL_KTRACE_LEVEL_ENABLED(level)>, TraceContext::Cpu, \
KTRACE_GRP_SCHEDULER, KTRACE_STRING_REF(string), flow_id, ##args)
#define LOCAL_KTRACE_COUNTER(level, string, value, args...) \
ktrace_counter(LocalTrace<LOCAL_KTRACE_LEVEL_ENABLED(level)>, KTRACE_GRP_SCHEDULER, \
KTRACE_STRING_REF(string), value, ##args)
template <size_t level>
using LocalTraceDuration = TraceDuration<TraceEnabled<LOCAL_KTRACE_LEVEL_ENABLED(level)>,
KTRACE_GRP_SCHEDULER, TraceContext::Cpu>;
// Enable/disable console traces local to this file.
#define LOCAL_TRACE 0
#define SCHED_LTRACEF(str, args...) LTRACEF("[%u] " str, arch_curr_cpu_num(), ##args)
#define SCHED_TRACEF(str, args...) TRACEF("[%u] " str, arch_curr_cpu_num(), ##args)
// Counters to track system load metrics.
KCOUNTER(demand_counter, "thread.demand_accum")
KCOUNTER(latency_counter, "thread.latency_accum")
KCOUNTER(runnable_counter, "thread.runnable_accum")
KCOUNTER(samples_counter, "thread.samples_accum")
namespace {
// Conversion table entry. Scales the integer argument to a fixed-point weight
// in the interval (0.0, 1.0].
struct WeightTableEntry {
constexpr WeightTableEntry(int64_t value)
: value{FromRatio<int64_t>(value, SchedWeight::Format::Power)} {}
constexpr operator SchedWeight() const { return value; }
const SchedWeight value;
};
// Table of fixed-point constants converting from kernel priority to fair
// scheduler weight.
constexpr WeightTableEntry kPriorityToWeightTable[] = {
121, 149, 182, 223, 273, 335, 410, 503, 616, 754, 924,
1132, 1386, 1698, 2080, 2549, 3122, 3825, 4685, 5739, 7030, 8612,
10550, 12924, 15832, 19394, 23757, 29103, 35651, 43672, 53499, 65536};
// Converts from kernel priority value in the interval [0, 31] to weight in the
// interval (0.0, 1.0]. See the definition of SchedWeight for an explanation of
// the weight distribution.
constexpr SchedWeight PriorityToWeight(int priority) { return kPriorityToWeightTable[priority]; }
// The minimum possible weight and its reciprocal.
constexpr SchedWeight kMinWeight = PriorityToWeight(LOWEST_PRIORITY);
constexpr SchedWeight kReciprocalMinWeight = 1 / kMinWeight;
// Utility operator to make expressions more succinct that update thread times
// and durations of basic types using the fixed-point counterparts.
constexpr zx_time_t& operator+=(zx_time_t& value, SchedDuration delta) {
value += delta.raw_value();
return value;
}
// Writes a context switch record to the ktrace buffer. This is always enabled
// so that user mode tracing can track which threads are running.
inline void TraceContextSwitch(const Thread* current_thread, const Thread* next_thread,
cpu_num_t current_cpu) {
const auto next_tid = static_cast<uint32_t>(next_thread->tid());
const SchedulerState& current_state = current_thread->scheduler_state();
const SchedulerState& next_state = next_thread->scheduler_state();
const uint32_t context = current_cpu | (current_thread->state() << 8) |
(current_state.base_priority() << 16) |
(next_state.base_priority() << 24);
const uint32_t current_relative_deadline =
current_state.discipline() == SchedDiscipline::Deadline
? static_cast<uint32_t>(current_state.deadline().deadline_ns.raw_value())
: 0u;
const uint32_t next_relative_deadline =
next_state.discipline() == SchedDiscipline::Deadline
? static_cast<uint32_t>(next_state.deadline().deadline_ns.raw_value())
: 0u;
ktrace(TAG_CONTEXT_SWITCH, next_tid, context, current_relative_deadline, next_relative_deadline);
}
// Returns true if the given thread is fair scheduled.
inline bool IsFairThread(const Thread* thread) {
return thread->scheduler_state().discipline() == SchedDiscipline::Fair;
}
// Returns true if the given thread is deadline scheduled.
inline bool IsDeadlineThread(const Thread* thread) {
return thread->scheduler_state().discipline() == SchedDiscipline::Deadline;
}
// Returns true if the given thread's time slice is adjustable under changes to
// the fair scheduler demand on the CPU.
inline bool IsThreadAdjustable(const Thread* thread) {
// Checking the thread state avoids unnecessary adjustments on a thread that
// is no longer competing.
return !thread->IsIdle() && IsFairThread(thread) && thread->state() == THREAD_READY;
}
// Returns a delta value to additively update a predictor. Compares the given
// sample to the current value of the predictor and returns a delta such that
// the predictor either exponentially peaks or decays toward the sample. The
// rate of decay depends on the alpha parameter, while the rate of peaking
// depends on the beta parameter. The predictor is not permitted to become
// negative.
//
// A single-rate exponential moving average is updated as follows:
//
// Sn = Sn-1 + a * (Yn - Sn-1)
//
// This function updates the exponential moving average using potentially
// different rates for peak and decay:
//
// D = Yn - Sn-1
// [ Sn-1 + a * D if D < 0
// Sn = [
// [ Sn-1 + b * D if D >= 0
//
template <typename T, typename Alpha, typename Beta>
constexpr T PeakDecayDelta(T value, T sample, Alpha alpha, Beta beta) {
const T delta = sample - value;
return ktl::max<T>(delta >= 0 ? T{beta * delta} : T{alpha * delta}, -value);
}
} // anonymous namespace
// Scales the given value up by the reciprocal of the CPU performance scale.
template <typename T>
inline T Scheduler::ScaleUp(T value) const {
return value * performance_scale_reciprocal();
}
// Scales the given value down by the CPU performance scale.
template <typename T>
inline T Scheduler::ScaleDown(T value) const {
return value * performance_scale();
}
// Returns a new flow id when flow tracing is enabled, zero otherwise.
inline uint64_t Scheduler::NextFlowId() {
if constexpr (LOCAL_KTRACE_LEVEL >= KTRACE_FLOW) {
return next_flow_id_.fetch_add(1);
}
return 0;
}
// Records details about the threads entering/exiting the run queues for various
// CPUs, as well as which task on each CPU is currently active. These events are
// used for trace analysis to compute statistics about overall utilization,
// taking CPU affinity into account.
inline void Scheduler::TraceThreadQueueEvent(StringRef* name, Thread* thread) {
// Traces marking the end of a queue/dequeue operation have arguments encoded
// as follows:
//
// arg0[56..63] : Number of runnable tasks on this CPU after the queue event.
// arg0[48..55] : CPU_ID of the affected queue.
// arg0[ 0..47] : Lowest 48 bits of thread TID/ptr.
// arg1[ 0..63] : CPU availability mask.
if constexpr (SCHEDULER_QUEUE_TRACING_ENABLED) {
const uint64_t tid =
thread->IsIdle()
? 0
: (thread->user_thread() ? thread->tid() : reinterpret_cast<uint64_t>(thread));
const size_t cnt = fair_run_queue_.size() + deadline_run_queue_.size() +
((active_thread_ && !active_thread_->IsIdle()) ? 1 : 0);
const uint64_t arg0 = (tid & 0xFFFFFFFFFFFF) |
(ktl::clamp<uint64_t>(this_cpu_, 0, 0xFF) << 48) |
(ktl::clamp<uint64_t>(cnt, 0, 0xFF) << 56);
const uint64_t arg1 = thread->scheduler_state().GetEffectiveCpuMask(mp_get_active_mask());
ktrace_probe(TraceAlways, TraceContext::Cpu, name, arg0, arg1);
}
}
// Updates the total expected runtime estimator with the given delta. The
// exported value is scaled by the relative performance factor of the CPU to
// account for performance differences in the estimate.
inline void Scheduler::UpdateTotalExpectedRuntime(SchedDuration delta_ns) {
total_expected_runtime_ns_ += delta_ns;
DEBUG_ASSERT(total_expected_runtime_ns_ >= 0);
const SchedDuration scaled_ns = ScaleUp(total_expected_runtime_ns_);
exported_total_expected_runtime_ns_ = scaled_ns;
LOCAL_KTRACE_COUNTER(KTRACE_COUNTER, "Est Load", scaled_ns.raw_value(), this_cpu());
}
// Updates the total deadline utilization estimator with the given delta. The
// exported value is scaled by the relative performance factor of the CPU to
// account for performance differences in the estimate.
inline void Scheduler::UpdateTotalDeadlineUtilization(SchedUtilization delta) {
total_deadline_utilization_ += delta;
DEBUG_ASSERT(total_deadline_utilization_ >= 0);
const SchedUtilization scaled = ScaleUp(total_deadline_utilization_);
exported_total_deadline_utilization_ = scaled;
LOCAL_KTRACE_COUNTER(KTRACE_COUNTER, "Est Util", Round<uint64_t>(scaled * 10000), this_cpu());
}
inline void Scheduler::TraceTotalRunnableThreads() const {
LOCAL_KTRACE_COUNTER(KTRACE_COUNTER, "Run-Q Len",
runnable_fair_task_count_ + runnable_deadline_task_count_, this_cpu());
}
void Scheduler::Dump(FILE* output_target) {
fprintf(output_target,
"\ttweight=%s nfair=%d ndeadline=%d vtime=%" PRId64 " period=%" PRId64 " tema=%" PRId64
" tutil=%s\n",
Format(weight_total_).c_str(), runnable_fair_task_count_, runnable_deadline_task_count_,
virtual_time_.raw_value(), scheduling_period_grans_.raw_value(),
total_expected_runtime_ns_.raw_value(), Format(total_deadline_utilization_).c_str());
if (active_thread_ != nullptr) {
const SchedulerState& state = active_thread_->scheduler_state();
if (IsFairThread(active_thread_)) {
fprintf(output_target,
"\t-> name=%s weight=%s start=%" PRId64 " finish=%" PRId64 " ts=%" PRId64
" ema=%" PRId64 "\n",
active_thread_->name(), Format(state.fair_.weight).c_str(),
state.start_time_.raw_value(), state.finish_time_.raw_value(),
state.time_slice_ns_.raw_value(), state.expected_runtime_ns_.raw_value());
} else {
fprintf(output_target,
"\t-> name=%s deadline=(%" PRId64 ", %" PRId64 ", %" PRId64 ") start=%" PRId64
" finish=%" PRId64 " ts=%" PRId64 " ema=%" PRId64 "\n",
active_thread_->name(), state.deadline_.capacity_ns.raw_value(),
state.deadline_.deadline_ns.raw_value(), state.deadline_.period_ns.raw_value(),
state.start_time_.raw_value(), state.finish_time_.raw_value(),
state.time_slice_ns_.raw_value(), state.expected_runtime_ns_.raw_value());
}
}
for (const Thread& thread : deadline_run_queue_) {
const SchedulerState& state = thread.scheduler_state();
fprintf(output_target,
"\t name=%s deadline=(%" PRId64 ", %" PRId64 ", %" PRId64 ") start=%" PRId64
" finish=%" PRId64 " ts=%" PRId64 " ema=%" PRId64 "\n",
thread.name(), state.deadline_.capacity_ns.raw_value(),
state.deadline_.deadline_ns.raw_value(), state.deadline_.period_ns.raw_value(),
state.start_time_.raw_value(), state.finish_time_.raw_value(),
state.time_slice_ns_.raw_value(), state.expected_runtime_ns_.raw_value());
}
for (const Thread& thread : fair_run_queue_) {
const SchedulerState& state = thread.scheduler_state();
fprintf(output_target,
"\t name=%s weight=%s start=%" PRId64 " finish=%" PRId64 " ts=%" PRId64
" ema=%" PRId64 "\n",
thread.name(), Format(state.fair_.weight).c_str(), state.start_time_.raw_value(),
state.finish_time_.raw_value(), state.time_slice_ns_.raw_value(),
state.expected_runtime_ns_.raw_value());
}
}
SchedWeight Scheduler::GetTotalWeight() const {
Guard<MonitoredSpinLock, IrqSave> guard{ThreadLock::Get(), SOURCE_TAG};
return weight_total_;
}
size_t Scheduler::GetRunnableTasks() const {
Guard<MonitoredSpinLock, IrqSave> guard{ThreadLock::Get(), SOURCE_TAG};
const int64_t total_runnable_tasks = runnable_fair_task_count_ + runnable_deadline_task_count_;
return static_cast<size_t>(total_runnable_tasks);
}
// Performs an augmented binary search for the task with the earliest finish
// time that also has a start time equal to or later than the given eligible
// time. An optional predicate may be supplied to filter candidates based on
// additional conditions.
//
// The tree is ordered by start time and is augmented by maintaining an
// additional invariant: each task node in the tree stores the minimum finish
// time of its descendents, including itself, in addition to its own start and
// finish time. The combination of these three values permits traversinng the
// tree along a perfect partition of minimum finish times with eligible start
// times.
//
// See kernel/scheduler_internal.h for an explanation of how the augmented
// invariant is maintained.
Thread* Scheduler::FindEarliestEligibleThread(RunQueue* run_queue, SchedTime eligible_time) {
return FindEarliestEligibleThread(run_queue, eligible_time, [](const auto iter) { return true; });
}
template <typename Predicate>
Thread* Scheduler::FindEarliestEligibleThread(RunQueue* run_queue, SchedTime eligible_time,
Predicate&& predicate) {
// Early out if there is no eligible thread.
if (run_queue->is_empty() || run_queue->front().scheduler_state().start_time_ > eligible_time) {
return nullptr;
}
// Deduces either Predicate& or const Predicate&, preserving the const
// qualification of the predicate.
decltype(auto) accept = ktl::forward<Predicate>(predicate);
auto node = run_queue->root();
auto subtree = run_queue->end();
auto path = run_queue->end();
// Descend the tree, with |node| following the path from the root to a leaf,
// such that the path partitions the tree into two parts: the nodes on the
// left represent eligible tasks, while the nodes on the right represent tasks
// that are not eligible. Eligible tasks are both in the left partition and
// along the search path, tracked by |path|.
while (node) {
if (node->scheduler_state().start_time_ <= eligible_time) {
if (!path || path->scheduler_state().finish_time_ > node->scheduler_state().finish_time_) {
path = node;
}
if (auto left = node.left();
!subtree || (left && subtree->scheduler_state().min_finish_time_ >
left->scheduler_state().min_finish_time_)) {
subtree = left;
}
node = node.right();
} else {
node = node.left();
}
}
if (!subtree) {
return path && accept(path) ? path.CopyPointer() : nullptr;
}
if (subtree->scheduler_state().min_finish_time_ >= path->scheduler_state().finish_time_ &&
accept(path)) {
return path.CopyPointer();
}
// Find the node with the earliest finish time among the decendents of the
// subtree with the smallest minimum finish time.
node = subtree;
do {
if (subtree->scheduler_state().min_finish_time_ == node->scheduler_state().finish_time_ &&
accept(node)) {
return node.CopyPointer();
}
if (auto left = node.left(); left && node->scheduler_state().min_finish_time_ ==
left->scheduler_state().min_finish_time_) {
node = left;
} else {
node = node.right();
}
} while (node);
return nullptr;
}
Scheduler* Scheduler::Get() { return Get(arch_curr_cpu_num()); }
Scheduler* Scheduler::Get(cpu_num_t cpu) { return &percpu::Get(cpu).scheduler; }
void Scheduler::InitializeThread(Thread* thread, int priority) {
new (&thread->scheduler_state()) SchedulerState{PriorityToWeight(priority)};
thread->scheduler_state().base_priority_ = priority;
thread->scheduler_state().effective_priority_ = priority;
thread->scheduler_state().inherited_priority_ = -1;
thread->scheduler_state().expected_runtime_ns_ = kDefaultMinimumGranularity;
}
void Scheduler::InitializeThread(Thread* thread, const zx_sched_deadline_params_t& params) {
new (&thread->scheduler_state()) SchedulerState{params};
// Set the numeric priority of the deadline task to the highest as a temporary
// workaround for the rest of the kernel not knowing about deadlines. This
// will cause deadline tasks to exert maximum fair scheduler pressure on fair
// tasks during PI interactions.
// TODO(eieio): Fix this with an abstraction that the higher layers can use
// to express priority / deadline more abstractly for PI and etc...
thread->scheduler_state().base_priority_ = HIGHEST_PRIORITY;
thread->scheduler_state().effective_priority_ = HIGHEST_PRIORITY;
thread->scheduler_state().inherited_priority_ = -1;
thread->scheduler_state().expected_runtime_ns_ = SchedDuration{params.capacity};
}
// Removes the thread at the head of the first eligible run queue. If there is
// an eligible deadline thread, it takes precedence over available fair
// threads. If there is no eligible work, attempt to steal work from other busy
// CPUs.
Thread* Scheduler::DequeueThread(SchedTime now) {
if (IsDeadlineThreadEligible(now)) {
return DequeueDeadlineThread(now);
}
if (likely(!fair_run_queue_.is_empty())) {
return DequeueFairThread();
}
if (Thread* const thread = StealWork(now); thread != nullptr) {
return thread;
}
return &percpu::Get(this_cpu()).idle_thread;
}
// Attempts to steal work from other busy CPUs and move it to the local run
// queues. Returns a pointer to the stolen thread that is now associated with
// the local Scheduler instance, or nullptr is no work was stolen.
Thread* Scheduler::StealWork(SchedTime now) {
LocalTraceDuration<KTRACE_DETAILED> trace{"steal_work"_stringref};
const cpu_num_t current_cpu = this_cpu();
const cpu_mask_t current_cpu_mask = cpu_num_to_mask(current_cpu);
const cpu_mask_t active_cpu_mask = mp_get_active_mask();
// Returns true if the given thread can run on this CPU.
const auto check_affinity = [current_cpu_mask, active_cpu_mask](const Thread& thread) -> bool {
return current_cpu_mask & thread.scheduler_state().GetEffectiveCpuMask(active_cpu_mask);
};
const CpuSearchSet& search_set = percpu::Get(current_cpu).search_set;
for (const auto& entry : search_set.const_iterator()) {
if (entry.cpu != current_cpu && active_cpu_mask & cpu_num_to_mask(entry.cpu)) {
Scheduler* const queue = Get(entry.cpu);
// Only steal across clusters if the target is above the load threshold.
if (cluster() != entry.cluster &&
queue->predicted_queue_time_ns() <= kInterClusterThreshold) {
continue;
}
// Returns true if the given thread in the run queue meets the criteria to
// run on this CPU.
const auto deadline_predicate = [this, check_affinity](const auto iter) {
const SchedulerState& state = iter->scheduler_state();
const SchedUtilization scaled_utilization = ScaleUp(state.deadline_.utilization);
const bool is_scheduleable = scaled_utilization <= kThreadUtilizationMax;
return check_affinity(*iter) && is_scheduleable && !iter->has_migrate_fn();
};
// Attempt to find a deadline thread that can run on this CPU.
Thread* thread =
FindEarliestEligibleThread(&queue->deadline_run_queue_, now, deadline_predicate);
if (thread != nullptr) {
DEBUG_ASSERT(!thread->has_migrate_fn());
DEBUG_ASSERT(check_affinity(*thread));
queue->deadline_run_queue_.erase(*thread);
queue->Remove(thread);
queue->TraceThreadQueueEvent("tqe_deque_steal_work"_stringref, thread);
// Associate the thread with this Scheduler, but don't enqueue it. It
// will run immediately on this CPU as if dequeued from a local queue.
Insert(now, thread, Placement::Association);
return thread;
}
// Returns true if the given thread in the run queue meets the criteria to
// run on this CPU.
const auto fair_predicate = [check_affinity](const auto iter) {
return check_affinity(*iter) && !iter->has_migrate_fn();
};
// TODO(eieio): Revisit the eligibility time parameter if/when moving to WF2Q.
queue->UpdateTimeline(now);
SchedTime eligible_time = queue->virtual_time_;
if (!queue->fair_run_queue_.is_empty()) {
const auto& earliest_thread = queue->fair_run_queue_.front();
const auto earliest_start = earliest_thread.scheduler_state().start_time_;
eligible_time = ktl::max(eligible_time, earliest_start);
}
thread = FindEarliestEligibleThread(&queue->fair_run_queue_, eligible_time, fair_predicate);
if (thread != nullptr) {
DEBUG_ASSERT(!thread->has_migrate_fn());
DEBUG_ASSERT(check_affinity(*thread));
queue->fair_run_queue_.erase(*thread);
queue->Remove(thread);
queue->TraceThreadQueueEvent("tqe_deque_steal_work"_stringref, thread);
// Associate the thread with this Scheduler, but don't enqueue it. It
// will run immediately on this CPU as if dequeued from a local queue.
Insert(now, thread, Placement::Association);
return thread;
}
}
}
return nullptr;
}
// Dequeues the eligible thread with the earliest virtual finish time. The
// caller must ensure that there is at least one thread in the queue.
Thread* Scheduler::DequeueFairThread() {
LocalTraceDuration<KTRACE_DETAILED> trace{"dequeue_fair_thread"_stringref};
// Snap the virtual clock to the earliest start time.
const auto& earliest_thread = fair_run_queue_.front();
const auto earliest_start = earliest_thread.scheduler_state().start_time_;
const SchedTime eligible_time = ktl::max(virtual_time_, earliest_start);
// Find the eligible thread with the earliest virtual finish time.
// Note: Currently, fair tasks are always eligible when added to the run
// queue, such that this search is equivalent to taking the front element of
// a tree sorted by finish time, instead of start time. However, when moving
// to the WF2Q algorithm, eligibility becomes a factor. Using the eligibility
// query now prepares for migrating the algorithm and also avoids having two
// different template instantiations of fbl::WAVLTree to support the fair and
// deadline disciplines.
Thread* const eligible_thread = FindEarliestEligibleThread(&fair_run_queue_, eligible_time);
DEBUG_ASSERT_MSG(eligible_thread != nullptr,
"virtual_time=%" PRId64 ", eligible_time=%" PRId64 " , start_time=%" PRId64
", finish_time=%" PRId64 ", min_finish_time=%" PRId64 "!",
virtual_time_.raw_value(), eligible_time.raw_value(),
earliest_thread.scheduler_state().start_time_.raw_value(),
earliest_thread.scheduler_state().finish_time_.raw_value(),
earliest_thread.scheduler_state().min_finish_time_.raw_value());
virtual_time_ = eligible_time;
fair_run_queue_.erase(*eligible_thread);
TraceThreadQueueEvent("tqe_deque_fair"_stringref, eligible_thread);
return eligible_thread;
}
// Dequeues the eligible thread with the earliest deadline. The caller must
// ensure that there is at least one eligible thread in the queue.
Thread* Scheduler::DequeueDeadlineThread(SchedTime eligible_time) {
LocalTraceDuration<KTRACE_DETAILED> trace{"dequeue_deadline_thread"_stringref};
Thread* const eligible_thread = FindEarliestEligibleThread(&deadline_run_queue_, eligible_time);
DEBUG_ASSERT_MSG(eligible_thread != nullptr,
"eligible_time=%" PRId64 ", start_time=%" PRId64 ", finish_time=%" PRId64
", min_finish_time=%" PRId64 "!",
eligible_time.raw_value(),
eligible_thread->scheduler_state().start_time_.raw_value(),
eligible_thread->scheduler_state().finish_time_.raw_value(),
eligible_thread->scheduler_state().min_finish_time_.raw_value());
deadline_run_queue_.erase(*eligible_thread);
TraceThreadQueueEvent("tqe_deque_deadline"_stringref, eligible_thread);
const SchedulerState& state = eligible_thread->scheduler_state();
trace.End(Round<uint64_t>(state.start_time_), Round<uint64_t>(state.finish_time_));
return eligible_thread;
}
// Returns the eligible thread with the earliest deadline that is also earlier
// than the given deadline. Returns nullptr if no threads meet this criteria or
// the run queue is empty.
Thread* Scheduler::FindEarlierDeadlineThread(SchedTime eligible_time, SchedTime finish_time) {
Thread* const eligible_thread = FindEarliestEligibleThread(&deadline_run_queue_, eligible_time);
const bool found_earlier_deadline =
eligible_thread && eligible_thread->scheduler_state().finish_time_ < finish_time;
return found_earlier_deadline ? eligible_thread : nullptr;
}
// Returns the time that the next deadline task will become eligible or infinite
// if there are no ready deadline tasks.
SchedTime Scheduler::GetNextEligibleTime() {
return deadline_run_queue_.is_empty() ? SchedTime{ZX_TIME_INFINITE}
: deadline_run_queue_.front().scheduler_state().start_time_;
}
// Dequeues the eligible thread with the earliest deadline that is also earlier
// than the given deadline. Returns nullptr if no threads meet the criteria or
// the run queue is empty.
Thread* Scheduler::DequeueEarlierDeadlineThread(SchedTime eligible_time, SchedTime finish_time) {
LocalTraceDuration<KTRACE_DETAILED> trace{"dequeue_earlier_deadline_thread"_stringref};
Thread* const eligible_thread = FindEarlierDeadlineThread(eligible_time, finish_time);
if (eligible_thread != nullptr) {
deadline_run_queue_.erase(*eligible_thread);
TraceThreadQueueEvent("tqe_deque_earlier_deadline"_stringref, eligible_thread);
}
return eligible_thread;
}
// Updates the system load metrics. Updates happen only when the active thread
// changes or the time slice expires.
void Scheduler::UpdateCounters(SchedDuration queue_time_ns) {
demand_counter.Add(weight_total_.raw_value());
runnable_counter.Add(runnable_fair_task_count_ + runnable_deadline_task_count_);
latency_counter.Add(queue_time_ns.raw_value());
samples_counter.Add(1);
}
// Selects a thread to run. Performs any necessary maintenance if the current
// thread is changing, depending on the reason for the change.
Thread* Scheduler::EvaluateNextThread(SchedTime now, Thread* current_thread, bool timeslice_expired,
SchedDuration scaled_total_runtime_ns) {
LocalTraceDuration<KTRACE_DETAILED> trace{"find_thread"_stringref};
const bool is_idle = current_thread->IsIdle();
const bool is_active = current_thread->state() == THREAD_READY;
const bool is_deadline = IsDeadlineThread(current_thread);
const bool is_new_deadline_eligible = IsDeadlineThreadEligible(now);
const cpu_num_t current_cpu = arch_curr_cpu_num();
const cpu_mask_t current_cpu_mask = cpu_num_to_mask(current_cpu);
const cpu_mask_t active_mask = mp_get_active_mask();
// Returns true when the given thread requires active migration.
const auto needs_migration = [active_mask, current_cpu_mask](Thread* const thread) {
// Threads may be created and resumed before the thread init level. Work
// around an empty active mask by assuming only the current cpu is available.
return active_mask != 0 &&
((thread->scheduler_state().GetEffectiveCpuMask(active_mask) & current_cpu_mask) == 0 ||
thread->scheduler_state().next_cpu_ != INVALID_CPU);
};
Thread* next_thread = nullptr;
if (is_active && needs_migration(current_thread)) {
// Avoid putting the current thread into the run queue in any of the paths
// below if it needs active migration. Let the migration loop below handle
// moving the thread. This avoids an edge case where time slice expiration
// coincides with an action that requires migration. Migration should take
// precedence over time slice expiration.
next_thread = current_thread;
} else if (is_active && likely(!is_idle)) {
if (timeslice_expired) {
// If the timeslice expired insert the current thread into the run queue.
QueueThread(current_thread, Placement::Insertion, now, scaled_total_runtime_ns);
} else if (is_new_deadline_eligible && is_deadline) {
// The current thread is deadline scheduled and there is at least one
// eligible deadline thread in the run queue: select the eligible thread
// with the earliest deadline, which may still be the current thread.
const SchedTime deadline_ns = current_thread->scheduler_state().finish_time_;
if (Thread* const earlier_thread = DequeueEarlierDeadlineThread(now, deadline_ns);
earlier_thread != nullptr) {
QueueThread(current_thread, Placement::Preemption, now, scaled_total_runtime_ns);
next_thread = earlier_thread;
} else {
// The current thread still has the earliest deadline.
next_thread = current_thread;
}
} else if (is_new_deadline_eligible && !is_deadline) {
// The current thread is fair scheduled and there is at least one eligible
// deadline thread in the run queue: return this thread to the run queue.
QueueThread(current_thread, Placement::Preemption, now, scaled_total_runtime_ns);
} else {
// The current thread has remaining time and no eligible contender.
next_thread = current_thread;
}
} else if (!is_active && likely(!is_idle)) {
// The current thread is no longer ready, remove its accounting.
Remove(current_thread);
}
// The current thread is no longer running or has returned to the run queue,
// select another thread to run.
if (next_thread == nullptr) {
next_thread = DequeueThread(now);
}
// If the next thread needs *active* migration, call the migration function,
// migrate the thread, and select another thread to run.
//
// Most migrations are passive. Passive migration happens whenever a thread
// becomes READY and a different CPU is selected than the last CPU the thread
// ran on.
//
// Active migration happens under the following conditions:
// 1. The CPU affinity of a thread that is READY or RUNNING is changed to
// exclude the CPU it is currently active on.
// 2. Passive migration, or active migration due to #1, selects a different
// CPU for a thread with a migration function. Migration to the next CPU
// is delayed until the migration function is called on the last CPU.
// 3. A thread that is READY or RUNNING is relocated by the periodic load
// balancer. NOT YET IMPLEMENTED.
//
cpu_mask_t cpus_to_reschedule_mask = 0;
for (; needs_migration(next_thread); next_thread = DequeueThread(now)) {
SchedulerState* const next_state = &next_thread->scheduler_state();
// If the thread is not scheduled to migrate to a specific CPU, find a
// suitable target CPU. If the thread has a migration function, the search
// will schedule the thread to migrate to a specific CPU and return the
// current CPU.
cpu_num_t target_cpu = INVALID_CPU;
if (next_state->next_cpu_ == INVALID_CPU) {
target_cpu = FindTargetCpu(next_thread);
DEBUG_ASSERT(target_cpu != this_cpu() || next_state->next_cpu_ != INVALID_CPU);
}
// If the thread is scheduled to migrate to a specific CPU, set the target
// to that CPU and call the migration function.
if (next_state->next_cpu_ != INVALID_CPU) {
DEBUG_ASSERT(next_state->last_cpu_ == this_cpu());
target_cpu = next_state->next_cpu_;
next_thread->CallMigrateFnLocked(Thread::MigrateStage::Before);
next_state->next_cpu_ = INVALID_CPU;
}
// The target CPU must always be different than the current CPU.
DEBUG_ASSERT(target_cpu != this_cpu());
// Remove accounting from this run queue and insert in the target run queue.
Remove(next_thread);
Scheduler* const target = Get(target_cpu);
target->Insert(now, next_thread);
cpus_to_reschedule_mask |= cpu_num_to_mask(target_cpu);
}
// Issue reschedule IPIs to CPUs with migrated threads.
mp_reschedule(cpus_to_reschedule_mask, 0);
return next_thread;
}
cpu_num_t Scheduler::FindTargetCpu(Thread* thread) {
LocalTraceDuration<KTRACE_DETAILED> trace{"find_target: cpu,avail"_stringref};
const cpu_num_t current_cpu = arch_curr_cpu_num();
const cpu_mask_t current_cpu_mask = cpu_num_to_mask(current_cpu);
const cpu_mask_t active_mask = mp_get_active_mask();
// Determine the set of CPUs the thread is allowed to run on.
//
// Threads may be created and resumed before the thread init level. Work around
// an empty active mask by assuming the current cpu is scheduleable.
const cpu_mask_t available_mask = active_mask != 0
? thread->scheduler_state().GetEffectiveCpuMask(active_mask)
: current_cpu_mask;
DEBUG_ASSERT_MSG(available_mask != 0,
"thread=%s affinity=%#x soft_affinity=%#x active=%#x "
"idle=%#x arch_ints_disabled=%d",
thread->name(), thread->scheduler_state().hard_affinity_,
thread->scheduler_state().soft_affinity_, active_mask, mp_get_idle_mask(),
arch_ints_disabled());
LOCAL_KTRACE(KTRACE_DETAILED, "target_mask: online,active", mp_get_online_mask(), active_mask);
const cpu_num_t last_cpu = thread->scheduler_state().last_cpu_;
const cpu_mask_t last_cpu_mask = cpu_num_to_mask(last_cpu);
// Find the best target CPU starting at the last CPU the task ran on, if any.
// Alternatives are considered in order of best to worst potential cache
// affinity.
const cpu_num_t starting_cpu = last_cpu != INVALID_CPU ? last_cpu : current_cpu;
const CpuSearchSet& search_set = percpu::Get(starting_cpu).search_set;
// Compares candidate queues and returns true if |queue_a| is a better
// alternative than |queue_b|. This is used by the target selection loop to
// determine whether the next candidate is better than the current target.
const auto compare = [thread](const Scheduler* queue_a,
const Scheduler* queue_b) TA_REQ(thread_lock) {
const SchedDuration a_predicted_queue_time_ns = queue_a->predicted_queue_time_ns();
const SchedDuration b_predicted_queue_time_ns = queue_b->predicted_queue_time_ns();
LocalTraceDuration<KTRACE_DETAILED> trace_compare{"compare: qtime,qtime"_stringref,
Round<uint64_t>(a_predicted_queue_time_ns),
Round<uint64_t>(b_predicted_queue_time_ns)};
if (IsFairThread(thread)) {
// CPUs in the same logical cluster are considered equivalent in terms of
// cache affinity. Choose the least loaded among the members of a cluster.
if (queue_a->cluster() == queue_b->cluster()) {
ktl::pair a{a_predicted_queue_time_ns, queue_a->predicted_deadline_utilization()};
ktl::pair b{b_predicted_queue_time_ns, queue_b->predicted_deadline_utilization()};
return a < b;
}
// When crossing a cluster boundary, compare both the candidate and
// current target to the threshold.
return a_predicted_queue_time_ns <= kInterClusterThreshold &&
b_predicted_queue_time_ns > kInterClusterThreshold;
} else {
const SchedUtilization utilization = thread->scheduler_state().deadline_.utilization;
const SchedUtilization scaled_utilization_a = queue_a->ScaleUp(utilization);
const SchedUtilization scaled_utilization_b = queue_b->ScaleUp(utilization);
ktl::pair a{scaled_utilization_a, a_predicted_queue_time_ns};
ktl::pair b{scaled_utilization_b, b_predicted_queue_time_ns};
ktl::pair a_prime{queue_a->predicted_deadline_utilization(), a};
ktl::pair b_prime{queue_b->predicted_deadline_utilization(), b};
return a_prime < b_prime;
}
};
// Determines whether the current target is sufficiently good to terminate the
// selection loop.
const auto is_sufficient = [thread](const Scheduler* queue) {
const SchedDuration candidate_queue_time_ns = queue->predicted_queue_time_ns();
LocalTraceDuration<KTRACE_DETAILED> sufficient_trace{"is_sufficient: thresh,qtime"_stringref,
Round<uint64_t>(kIntraClusterThreshold),
Round<uint64_t>(candidate_queue_time_ns)};
if (IsFairThread(thread)) {
return candidate_queue_time_ns <= kIntraClusterThreshold;
}
const SchedUtilization predicted_utilization = queue->predicted_deadline_utilization();
const SchedUtilization utilization = thread->scheduler_state().deadline_.utilization;
const SchedUtilization scaled_utilization = queue->ScaleUp(utilization);
return candidate_queue_time_ns <= kIntraClusterThreshold &&
scaled_utilization <= kThreadUtilizationMax &&
predicted_utilization + scaled_utilization <= kCpuUtilizationLimit;
};
// Loop over the search set for CPU the task last ran on to find a suitable
// target.
cpu_num_t target_cpu = INVALID_CPU;
Scheduler* target_queue = nullptr;
for (const auto& entry : search_set.const_iterator()) {
const cpu_num_t candidate_cpu = entry.cpu;
const bool candidate_available = available_mask & cpu_num_to_mask(candidate_cpu);
Scheduler* const candidate_queue = Get(candidate_cpu);
if (candidate_available &&
(target_queue == nullptr || compare(candidate_queue, target_queue))) {
target_cpu = candidate_cpu;
target_queue = candidate_queue;
// Stop searching at the first sufficiently unloaded CPU.
if (is_sufficient(target_queue)) {
break;
}
}
}
DEBUG_ASSERT(target_cpu != INVALID_CPU);
SCHED_LTRACEF("thread=%s target_cpu=%u\n", thread->name(), target_cpu);
trace.End(last_cpu, target_cpu);
bool delay_migration = last_cpu != target_cpu && last_cpu != INVALID_CPU &&
thread->has_migrate_fn() && (active_mask & last_cpu_mask) != 0;
if (unlikely(delay_migration)) {
thread->scheduler_state().next_cpu_ = target_cpu;
return last_cpu;
} else {
return target_cpu;
}
}
void Scheduler::UpdateTimeline(SchedTime now) {
LocalTraceDuration<KTRACE_DETAILED> trace{"update_vtime"_stringref};
const auto runtime_ns = now - last_update_time_ns_;
last_update_time_ns_ = now;
if (weight_total_ > SchedWeight{0}) {
virtual_time_ += runtime_ns;
}
trace.End(Round<uint64_t>(runtime_ns), Round<uint64_t>(virtual_time_));
}
void Scheduler::RescheduleCommon(SchedTime now, EndTraceCallback end_outer_trace) {
LocalTraceDuration<KTRACE_DETAILED> trace{"reschedule_common"_stringref, Round<uint64_t>(now), 0};
const cpu_num_t current_cpu = arch_curr_cpu_num();
Thread* const current_thread = Thread::Current::Get();
SchedulerState* const current_state = &current_thread->scheduler_state();
DEBUG_ASSERT(arch_ints_disabled());
DEBUG_ASSERT(thread_lock.IsHeld());
// Aside from the thread_lock, spinlocks should never be held over a reschedule.
DEBUG_ASSERT(arch_num_spinlocks_held() == 1);
DEBUG_ASSERT_MSG(current_thread->state() != THREAD_RUNNING, "state %d\n",
current_thread->state());
DEBUG_ASSERT(!arch_blocking_disallowed());
DEBUG_ASSERT_MSG(current_cpu == this_cpu(), "current_cpu=%u this_cpu=%u", current_cpu,
this_cpu());
CPU_STATS_INC(reschedules);
UpdateTimeline(now);
const SchedDuration total_runtime_ns = now - start_of_current_time_slice_ns_;
const SchedDuration actual_runtime_ns = now - current_state->last_started_running_;
current_state->last_started_running_ = now;
current_thread->UpdateSchedulerStats({.state = current_thread->state(),
.state_time = now.raw_value(),
.cpu_time = actual_runtime_ns.raw_value()});
// Update the runtime accounting for the thread that just ran.
current_state->runtime_ns_ += actual_runtime_ns;
// Adjust the rate of the current thread when demand changes. Changes in
// demand could be due to threads entering or leaving the run queue, or due
// to weights changing in the current or enqueued threads.
if (IsThreadAdjustable(current_thread) && weight_total_ != scheduled_weight_total_ &&
total_runtime_ns < current_state->time_slice_ns_) {
LocalTraceDuration<KTRACE_DETAILED> trace_adjust_rate{"adjust_rate"_stringref};
scheduled_weight_total_ = weight_total_;
const SchedDuration time_slice_ns = CalculateTimeslice(current_thread);
const SchedDuration remaining_time_slice_ns =
time_slice_ns * current_state->fair_.normalized_timeslice_remainder;
const bool timeslice_changed = time_slice_ns != current_state->fair_.initial_time_slice_ns;
const bool timeslice_remaining = total_runtime_ns < remaining_time_slice_ns;
// Update the preemption timer if necessary.
if (timeslice_changed && timeslice_remaining) {
target_preemption_time_ns_ = start_of_current_time_slice_ns_ + remaining_time_slice_ns;
const SchedTime preemption_time_ns = ClampToDeadline(target_preemption_time_ns_);
DEBUG_ASSERT(preemption_time_ns <= target_preemption_time_ns_);
percpu::Get(current_cpu).timer_queue.PreemptReset(preemption_time_ns.raw_value());
}
current_state->fair_.initial_time_slice_ns = time_slice_ns;
current_state->time_slice_ns_ = remaining_time_slice_ns;
trace_adjust_rate.End(Round<uint64_t>(remaining_time_slice_ns),
Round<uint64_t>(total_runtime_ns));
}
// Scale the total runtime of deadline tasks by the relative performance of
// the CPU, effectively increasing the capacity of the task in proportion to
// the performance ratio.
const SchedDuration scaled_total_runtime_ns =
IsDeadlineThread(current_thread) ? ScaleDown(total_runtime_ns) : total_runtime_ns;
// A deadline can expire when there is still time left in the time slice if
// the task wakes up late. This is handled the same as the time slice
// expiring.
const bool deadline_expired =
IsDeadlineThread(current_thread) && now >= current_state->finish_time_;
const bool timeslice_expired =
deadline_expired || scaled_total_runtime_ns >= current_state->time_slice_ns_;
// Check the consistency of the target preemption time and the current time
// slice.
DEBUG_ASSERT_MSG(
now < target_preemption_time_ns_ || timeslice_expired,
"capacity_ns=%" PRId64 " deadline_ns=%" PRId64 " now=%" PRId64
" target_preemption_time_ns=%" PRId64 " total_runtime_ns=%" PRId64
" scaled_total_runtime_ns=%" PRId64 " finish_time=%" PRId64 " time_slice_ns=%" PRId64
" start_of_current_time_slice_ns=%" PRId64,
IsDeadlineThread(current_thread) ? current_state->deadline_.capacity_ns.raw_value() : 0,
IsDeadlineThread(current_thread) ? current_state->deadline_.deadline_ns.raw_value() : 0,
now.raw_value(), target_preemption_time_ns_.raw_value(), total_runtime_ns.raw_value(),
scaled_total_runtime_ns.raw_value(), current_state->finish_time_.raw_value(),
current_state->time_slice_ns_.raw_value(), start_of_current_time_slice_ns_.raw_value());
// Select a thread to run.
Thread* const next_thread =
EvaluateNextThread(now, current_thread, timeslice_expired, scaled_total_runtime_ns);
DEBUG_ASSERT(next_thread != nullptr);
SchedulerState* const next_state = &next_thread->scheduler_state();
SCHED_LTRACEF("current={%s, %s} next={%s, %s} expired=%d total_runtime_ns=%" PRId64
" fair_front=%s deadline_front=%s\n",
current_thread->name(), ToString(current_thread->state()), next_thread->name(),
ToString(next_thread->state()), timeslice_expired, total_runtime_ns.raw_value(),
fair_run_queue_.is_empty() ? "[none]" : fair_run_queue_.front().name(),
deadline_run_queue_.is_empty() ? "[none]" : deadline_run_queue_.front().name());
// Flush pending preemptions.
mp_reschedule(current_thread->preemption_state().preempts_pending_, 0);
current_thread->preemption_state().preempts_pending_ = 0;
// Update the state of the current and next thread.
next_thread->set_running();
next_state->last_cpu_ = current_cpu;
next_state->curr_cpu_ = current_cpu;
active_thread_ = next_thread;
// Trace the activation of the next thread before context switching.
if (current_thread != next_thread) {
TraceThreadQueueEvent("tqe_activate"_stringref, next_thread);
}
// Handle any pending migration work.
next_thread->CallMigrateFnLocked(Thread::MigrateStage::After);
// Update the expected runtime of the current thread and the per-CPU total.
// Only update the thread and aggregate values if the current thread is still
// associated with this CPU or is no longer ready.
const bool current_is_associated =
!current_state->active() || current_state->curr_cpu_ == current_cpu;
if (!current_thread->IsIdle() && current_is_associated &&
(timeslice_expired || current_thread != next_thread)) {
LocalTraceDuration<KTRACE_DETAILED> update_ema_trace{"update_expected_runtime"_stringref};
// Adjust the runtime for the relative performance of the CPU to account for
// different performance levels in the estimate. The relative performance
// scale is in the range (0.0, 1.0], such that the adjusted runtime is
// always less than or equal to the monotonic runtime.
const SchedDuration adjusted_total_runtime_ns = ScaleDown(total_runtime_ns);
current_state->banked_runtime_ns_ += adjusted_total_runtime_ns;
if (timeslice_expired || !current_state->active()) {
const SchedDuration delta_ns =
PeakDecayDelta(current_state->expected_runtime_ns_, current_state->banked_runtime_ns_,
kExpectedRuntimeAlpha, kExpectedRuntimeBeta);
current_state->expected_runtime_ns_ += delta_ns;
current_state->banked_runtime_ns_ = SchedDuration{0};
// Adjust the aggregate value by the same amount. The adjustment is only
// necessary when the thread is still active on this CPU.
if (current_state->active()) {
UpdateTotalExpectedRuntime(delta_ns);
}
}
}
// Always call to handle races between reschedule IPIs and changes to the run
// queue.
mp_prepare_current_cpu_idle_state(next_thread->IsIdle());
if (next_thread->IsIdle()) {
mp_set_cpu_idle(current_cpu);
} else {
mp_set_cpu_busy(current_cpu);
}
if (current_thread->IsIdle()) {
percpu::Get(current_cpu).stats.idle_time += actual_runtime_ns;
}
if (next_thread->IsIdle()) {
LocalTraceDuration<KTRACE_DETAILED> trace_stop_preemption{"idle"_stringref};
SCHED_LTRACEF("Idle: current=%s next=%s\n", current_thread->name(), next_thread->name());
UpdateCounters(SchedDuration{0});
next_state->last_started_running_ = now;
// If there are no tasks to run in the future, disable the preemption timer.
// Otherwise, set the preemption time to the earliest eligible time.
target_preemption_time_ns_ = GetNextEligibleTime();
percpu::Get(current_cpu).timer_queue.PreemptReset(target_preemption_time_ns_.raw_value());
} else if (timeslice_expired || next_thread != current_thread) {
LocalTraceDuration<KTRACE_DETAILED> trace_start_preemption{"next_slice: preempt,abs"_stringref};
// Re-compute the time slice and deadline for the new thread based on the
// latest state.
target_preemption_time_ns_ = NextThreadTimeslice(next_thread, now);
// Compute the time the next thread spent in the run queue. The value of
// last_started_running for the current thread is updated at the top of
// this method: when the current and next thread are the same, the queue
// time is zero. Otherwise, last_started_running is the time the next thread
// entered the run queue.
const SchedDuration queue_time_ns = now - next_state->last_started_running_;
UpdateCounters(queue_time_ns);
next_thread->UpdateSchedulerStats({.state = next_thread->state(),
.state_time = now.raw_value(),
.queue_time = queue_time_ns.raw_value()});
next_state->last_started_running_ = now;
start_of_current_time_slice_ns_ = now;
scheduled_weight_total_ = weight_total_;
SCHED_LTRACEF("Start preempt timer: current=%s next=%s now=%" PRId64 " deadline=%" PRId64 "\n",
current_thread->name(), next_thread->name(), now.raw_value(),
target_preemption_time_ns_.raw_value());
// Adjust the preemption time to account for a deadline thread becoming
// eligible before the current time slice expires.
const SchedTime preemption_time_ns =
IsFairThread(next_thread)
? ClampToDeadline(target_preemption_time_ns_)
: ClampToEarlierDeadline(target_preemption_time_ns_, next_state->finish_time_);
DEBUG_ASSERT(preemption_time_ns <= target_preemption_time_ns_);
percpu::Get(current_cpu).timer_queue.PreemptReset(preemption_time_ns.raw_value());
trace_start_preemption.End(Round<uint64_t>(preemption_time_ns),
Round<uint64_t>(target_preemption_time_ns_));
// Emit a flow end event to match the flow begin event emitted when the
// thread was enqueued. Emitting in this scope ensures that thread just
// came from the run queue (and is not the idle thread).
LOCAL_KTRACE_FLOW_END(KTRACE_FLOW, "sched_latency", next_state->flow_id(), next_thread->tid());
} else {
LocalTraceDuration<KTRACE_DETAILED> trace_continue{"continue: preempt,abs"_stringref};
// The current thread should continue to run. A throttled deadline thread
// might become eligible before the current time slice expires. Figure out
// whether to set the preemption time earlier to switch to the newly
// eligible thread.
//
// The preemption time should be set earlier when either:
// * Current is a fair thread and a deadline thread will become eligible
// before its time slice expires.
// * Current is a deadline thread and a deadline thread with an earlier
// deadline will become eligible before its time slice expires.
//
// Note that the target preemption time remains set to the ideal
// preemption time for the current task, even if the preemption timer is set
// earlier. If a task that becomes eligible is stolen before the early
// preemption is handled, this logic will reset to the original target
// preemption time.
const SchedTime preemption_time_ns =
IsFairThread(next_thread)
? ClampToDeadline(target_preemption_time_ns_)
: ClampToEarlierDeadline(target_preemption_time_ns_, next_state->finish_time_);
DEBUG_ASSERT(preemption_time_ns <= target_preemption_time_ns_);
percpu::Get(current_cpu).timer_queue.PreemptReset(preemption_time_ns.raw_value());
trace_continue.End(Round<uint64_t>(preemption_time_ns),
Round<uint64_t>(target_preemption_time_ns_));
}
// Assert that there is no path beside running the idle thread can leave the
// preemption timer unarmed. However, the preemption timer may or may not be
// armed when running the idle thread.
// TODO(eieio): In the future, the preemption timer may be canceled when there
// is only one task available to run. Revisit this assertion at that time.
DEBUG_ASSERT(next_thread->IsIdle() || percpu::Get(current_cpu).timer_queue.PreemptArmed());
if (next_thread != current_thread) {
LOCAL_KTRACE(KTRACE_DETAILED, "reschedule current: count,slice",
runnable_fair_task_count_ + runnable_deadline_task_count_,
Round<uint64_t>(current_thread->scheduler_state().time_slice_ns_));
LOCAL_KTRACE(KTRACE_DETAILED, "reschedule next: wsum,slice", weight_total_.raw_value(),
Round<uint64_t>(next_thread->scheduler_state().time_slice_ns_));
TraceContextSwitch(current_thread, next_thread, current_cpu);
SCHED_LTRACEF("current=(%s, flags 0x%#x) next=(%s, flags 0x%#x)\n", current_thread->name(),
current_thread->flags(), next_thread->name(), next_thread->flags());
if (current_thread->aspace() != next_thread->aspace()) {
vmm_context_switch(current_thread->aspace(), next_thread->aspace());
}
CPU_STATS_INC(context_switches);
// Prevent the scheduler durations from spanning the context switch.
// Some context switches do not resume within this method on the other
// thread, which results in unterminated durations. All of the callers
// with durations tail-call this method, so terminating the duration
// here should not cause significant inaccuracy of the outer duration.
trace.End();
if (end_outer_trace) {
end_outer_trace();
}
arch_context_switch(current_thread, next_thread);
}
}
void Scheduler::UpdatePeriod() {
LocalTraceDuration<KTRACE_DETAILED> trace{"update_period"_stringref};
DEBUG_ASSERT(runnable_fair_task_count_ >= 0);
DEBUG_ASSERT(minimum_granularity_ns_ > 0);
DEBUG_ASSERT(target_latency_grans_ > 0);
const int64_t num_tasks = runnable_fair_task_count_;
const int64_t normal_tasks = Round<int64_t>(target_latency_grans_);
// The scheduling period stretches when there are too many tasks to fit
// within the target latency.
scheduling_period_grans_ = SchedDuration{num_tasks > normal_tasks ? num_tasks : normal_tasks};
SCHED_LTRACEF("num_tasks=%" PRId64 " normal_tasks=%" PRId64 " period_grans=%" PRId64 "\n",
num_tasks, normal_tasks, scheduling_period_grans_.raw_value());
trace.End(Round<uint64_t>(scheduling_period_grans_), num_tasks);
}
SchedDuration Scheduler::CalculateTimeslice(Thread* thread) {
LocalTraceDuration<KTRACE_DETAILED> trace{"calculate_timeslice: w,wt"_stringref};
SchedulerState* const state = &thread->scheduler_state();
// Calculate the relative portion of the scheduling period.
const SchedWeight proportional_time_slice_grans =
scheduling_period_grans_ * state->fair_.weight / weight_total_;
// Ensure that the time slice is at least the minimum granularity.
const int64_t time_slice_grans = Round<int64_t>(proportional_time_slice_grans);
const int64_t minimum_time_slice_grans = time_slice_grans > 0 ? time_slice_grans : 1;
// Calcluate the time slice in nanoseconds.
const SchedDuration time_slice_ns = minimum_time_slice_grans * minimum_granularity_ns_;
trace.End(state->fair_.weight.raw_value(), weight_total_.raw_value());
return time_slice_ns;
}
SchedTime Scheduler::ClampToDeadline(SchedTime completion_time) {
return ktl::min(completion_time, GetNextEligibleTime());
}
SchedTime Scheduler::ClampToEarlierDeadline(SchedTime completion_time, SchedTime finish_time) {
Thread* const thread = FindEarlierDeadlineThread(completion_time, finish_time);
return thread ? ktl::min(completion_time, thread->scheduler_state().start_time_)
: completion_time;
}
SchedTime Scheduler::NextThreadTimeslice(Thread* thread, SchedTime now) {
LocalTraceDuration<KTRACE_DETAILED> trace{"next_timeslice: t,abs"_stringref};
SchedulerState* const state = &thread->scheduler_state();
SchedTime target_preemption_time_ns;
if (IsFairThread(thread)) {
// Calculate the next time slice and the deadline when the time slice is
// completed.
const SchedDuration time_slice_ns = CalculateTimeslice(thread);
const SchedDuration remaining_time_slice_ns =
time_slice_ns * state->fair_.normalized_timeslice_remainder;
DEBUG_ASSERT(time_slice_ns > 0);
DEBUG_ASSERT(remaining_time_slice_ns > 0);
state->fair_.initial_time_slice_ns = time_slice_ns;
state->time_slice_ns_ = remaining_time_slice_ns;
target_preemption_time_ns = now + remaining_time_slice_ns;
DEBUG_ASSERT_MSG(state->time_slice_ns_ > 0 && target_preemption_time_ns > now,
"time_slice_ns=%" PRId64 " now=%" PRId64 " target_preemption_time_ns=%" PRId64,
state->time_slice_ns_.raw_value(), now.raw_value(),
target_preemption_time_ns.raw_value());
SCHED_LTRACEF("name=%s weight_total=%#x weight=%#x time_slice_ns=%" PRId64 "\n", thread->name(),
static_cast<uint32_t>(weight_total_.raw_value()),
static_cast<uint32_t>(state->fair_.weight.raw_value()),
state->time_slice_ns_.raw_value());
trace.End(Round<uint64_t>(state->time_slice_ns_), Round<uint64_t>(target_preemption_time_ns));
} else {
// Calculate the deadline when the remaining time slice is completed. The
// time slice is maintained by the deadline queuing logic, no need to update
// it here. The target preemption time is based on the time slice scaled by
// the performance of the CPU and clamped to the deadline. This increases
// capacity on slower processors, however, bandwidth isolation is preserved
// because CPU selection attempts to keep scaled total capacity below one.
const SchedDuration scaled_time_slice_ns = ScaleUp(state->time_slice_ns_);
target_preemption_time_ns =
ktl::min<SchedTime>(now + scaled_time_slice_ns, state->finish_time_);
SCHED_LTRACEF("name=%s capacity=%" PRId64 " deadline=%" PRId64 " period=%" PRId64
" scaled_time_slice_ns=%" PRId64 "\n",
thread->name(), state->deadline_.capacity_ns.raw_value(),
state->deadline_.deadline_ns.raw_value(), state->deadline_.period_ns.raw_value(),
scaled_time_slice_ns.raw_value());
trace.End(Round<uint64_t>(scaled_time_slice_ns), Round<uint64_t>(target_preemption_time_ns));
}
return target_preemption_time_ns;
}
void Scheduler::QueueThread(Thread* thread, Placement placement, SchedTime now,
SchedDuration scaled_total_runtime_ns) {
LocalTraceDuration<KTRACE_DETAILED> trace{"queue_thread: s,f"_stringref};
DEBUG_ASSERT(thread->state() == THREAD_READY);
DEBUG_ASSERT(!thread->IsIdle());
DEBUG_ASSERT(placement != Placement::Association);
SCHED_LTRACEF("QueueThread: thread=%s\n", thread->name());
SchedulerState* const state = &thread->scheduler_state();
// Account for the consumed time slice. The consumed time is zero when the
// thread is unblocking, migrating, or adjusting queue position. The
// remaining time slice may become negative due to scheduler overhead.
state->time_slice_ns_ -= scaled_total_runtime_ns;
if (IsFairThread(thread)) {
// Compute the ratio of remaining time slice to ideal time slice. This may
// be less than 1.0 due to time slice consumed or due to previous preemption
// by a deadline task or both.
const SchedRemainder normalized_timeslice_remainder =
state->time_slice_ns_ / ktl::max(state->fair_.initial_time_slice_ns, SchedDuration{1});
DEBUG_ASSERT_MSG(
normalized_timeslice_remainder <= SchedRemainder{1},
"time_slice_ns=%" PRId64 " initial_time_slice_ns=%" PRId64 " remainder=%" PRId64 "\n",
state->time_slice_ns_.raw_value(), state->fair_.initial_time_slice_ns.raw_value(),
normalized_timeslice_remainder.raw_value());
if (placement == Placement::Insertion || normalized_timeslice_remainder <= 0) {
state->start_time_ = ktl::max(state->finish_time_, virtual_time_);
state->fair_.normalized_timeslice_remainder = SchedRemainder{1};
} else if (placement == Placement::Preemption) {
DEBUG_ASSERT(state->time_slice_ns_ > 0);
state->fair_.normalized_timeslice_remainder = normalized_timeslice_remainder;
}
const SchedDuration scheduling_period_ns = scheduling_period_grans_ * minimum_granularity_ns_;
const SchedWeight rate = kReciprocalMinWeight * state->fair_.weight;
const SchedDuration delta_norm = scheduling_period_ns / rate;
state->finish_time_ = state->start_time_ + delta_norm;
DEBUG_ASSERT_MSG(state->start_time_ < state->finish_time_,
"start=%" PRId64 " finish=%" PRId64 " delta_norm=%" PRId64 "\n",
state->start_time_.raw_value(), state->finish_time_.raw_value(),
delta_norm.raw_value());
} else {
// Both a new insertion into the run queue or a re-insertion due to
// preemption can happen after the time slice and/or deadline expires.
if (placement == Placement::Insertion || placement == Placement::Preemption) {
const auto string_ref = placement == Placement::Insertion
? "insert_deadline: r,c"_stringref
: "preemption_deadline: r,c"_stringref;
LocalTraceDuration<KTRACE_DETAILED> deadline_trace{string_ref};
// Determine how much time is left before the deadline. This might be less
// than the remaining time slice or negative if the thread blocked.
const SchedDuration time_until_deadline_ns = state->finish_time_ - now;
if (time_until_deadline_ns <= 0 || state->time_slice_ns_ <= 0) {
const SchedTime period_finish_ns = state->start_time_ + state->deadline_.period_ns;
state->start_time_ = now >= period_finish_ns ? now : period_finish_ns;
state->finish_time_ = state->start_time_ + state->deadline_.deadline_ns;
state->time_slice_ns_ = state->deadline_.capacity_ns;
} else if (state->time_slice_ns_ >= time_until_deadline_ns) {
state->time_slice_ns_ = time_until_deadline_ns;
}
DEBUG_ASSERT(state->time_slice_ns_ >= 0);
deadline_trace.End(Round<uint64_t>(time_until_deadline_ns),
Round<uint64_t>(state->time_slice_ns_));
}
DEBUG_ASSERT_MSG(state->start_time_ < state->finish_time_,
"start=%" PRId64 " finish=%" PRId64 " capacity=%" PRId64 "\n",
state->start_time_.raw_value(), state->finish_time_.raw_value(),
state->time_slice_ns_.raw_value());
}
// Only update the generation, enqueue time, and emit a flow event if this
// is an insertion, preemption, or migration. In contrast, an adjustment only
// changes the queue position in the same queue due to a parameter change and
// should not perform these actions.
if (placement != Placement::Adjustment) {
if (placement == Placement::Migration) {
// Connect the flow into the previous queue to the new queue.
LOCAL_KTRACE_FLOW_STEP(KTRACE_FLOW, "sched_latency", state->flow_id(), thread->tid());
} else {
// Reuse this member to track the time the thread enters the run queue. It
// is not read outside of the scheduler unless the thread state is
// THREAD_RUNNING.
state->last_started_running_ = now;
state->flow_id_ = NextFlowId();
LOCAL_KTRACE_FLOW_BEGIN(KTRACE_FLOW, "sched_latency", state->flow_id(), thread->tid());
}
// The generation count must always be updated when changing between CPUs,
// as each CPU has its own generation count.
state->generation_ = ++generation_count_;
}
// Insert the thread into the appropriate run queue after the generation count
// is potentially updated above.
if (IsFairThread(thread)) {
fair_run_queue_.insert(thread);
} else {
deadline_run_queue_.insert(thread);
}
TraceThreadQueueEvent("tqe_enque"_stringref, thread);
trace.End(Round<uint64_t>(state->start_time_), Round<uint64_t>(state->finish_time_));
}
void Scheduler::Insert(SchedTime now, Thread* thread, Placement placement) {
LocalTraceDuration<KTRACE_DETAILED> trace{"insert"_stringref};
DEBUG_ASSERT(thread->state() == THREAD_READY);
DEBUG_ASSERT(!thread->IsIdle());
SchedulerState* const state = &thread->scheduler_state();
// Ensure insertion happens only once, even if Unblock is called multiple times.
if (state->OnInsert()) {
// Insertion can happen from a different CPU. Set the thread's current
// CPU to the one this scheduler instance services.
state->curr_cpu_ = this_cpu();
UpdateTotalExpectedRuntime(state->expected_runtime_ns_);
if (IsFairThread(thread)) {
runnable_fair_task_count_++;
DEBUG_ASSERT(runnable_fair_task_count_ > 0);
UpdateTimeline(now);
UpdatePeriod();
weight_total_ += state->fair_.weight;
DEBUG_ASSERT(weight_total_ > 0);
} else {
UpdateTotalDeadlineUtilization(state->deadline_.utilization);
runnable_deadline_task_count_++;
DEBUG_ASSERT(runnable_deadline_task_count_ != 0);
}
TraceTotalRunnableThreads();
if (placement != Placement::Association) {
QueueThread(thread, placement, now);
} else {
// Connect the flow into the previous queue to the new queue.
LOCAL_KTRACE_FLOW_STEP(KTRACE_FLOW, "sched_latency", state->flow_id(), thread->tid());
}
}
}
void Scheduler::Remove(Thread* thread) {
LocalTraceDuration<KTRACE_DETAILED> trace{"remove"_stringref};
DEBUG_ASSERT(!thread->IsIdle());
SchedulerState* const state = &thread->scheduler_state();
DEBUG_ASSERT(!state->InQueue());
// Ensure that removal happens only once, even if Block() is called multiple times.
if (state->OnRemove()) {
state->curr_cpu_ = INVALID_CPU;
UpdateTotalExpectedRuntime(-state->expected_runtime_ns_);
if (IsFairThread(thread)) {
DEBUG_ASSERT(runnable_fair_task_count_ > 0);
runnable_fair_task_count_--;
UpdatePeriod();
state->start_time_ = SchedNs(0);
state->finish_time_ = SchedNs(0);
weight_total_ -= state->fair_.weight;
DEBUG_ASSERT(weight_total_ >= 0);
SCHED_LTRACEF("name=%s weight_total=%s weight=%s\n", thread->name(),
Format(weight_total_).c_str(), Format(state->fair_.weight).c_str());
} else {
UpdateTotalDeadlineUtilization(-state->deadline_.utilization);
DEBUG_ASSERT(runnable_deadline_task_count_ > 0);
runnable_deadline_task_count_--;
}
TraceTotalRunnableThreads();
}
}
inline void Scheduler::RescheduleMask(cpu_mask_t cpus_to_reschedule_mask) {
PreemptionState& preemption_state = Thread::Current::Get()->preemption_state();
if (preemption_state.EagerReschedDisableCount() != 0) {
preemption_state.preempts_pending_ |= cpus_to_reschedule_mask;
} else {
mp_reschedule(cpus_to_reschedule_mask, 0);
}
if (preemption_state.PreemptIsEnabled() &&
cpus_to_reschedule_mask & cpu_num_to_mask(arch_curr_cpu_num())) {
// TODO(fxbug.dev/64884): Once spinlocks imply preempt disable, this if-else can be replaced
// with a call to Preempt().
if (arch_num_spinlocks_held() < 2 && !arch_blocking_disallowed()) {
Preempt();
} else {
preemption_state.preempts_pending_ |= cpu_num_to_mask(arch_curr_cpu_num());
}
}
}
void Scheduler::Block() {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_block"_stringref};
DEBUG_ASSERT(thread_lock.IsHeld());
Thread* const current_thread = Thread::Current::Get();
current_thread->canary().Assert();
DEBUG_ASSERT(current_thread->state() != THREAD_RUNNING);
const SchedTime now = CurrentTime();
SCHED_LTRACEF("current=%s now=%" PRId64 "\n", current_thread->name(), now.raw_value());
Scheduler::Get()->RescheduleCommon(now, trace.Completer());
}
void Scheduler::Unblock(Thread* thread) {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_unblock"_stringref};
thread->canary().Assert();
DEBUG_ASSERT(thread_lock.IsHeld());
const SchedTime now = CurrentTime();
SCHED_LTRACEF("thread=%s now=%" PRId64 "\n", thread->name(), now.raw_value());
const cpu_num_t target_cpu = FindTargetCpu(thread);
Scheduler* const target = Get(target_cpu);
thread->set_ready();
target->Insert(now, thread);
trace.End();
RescheduleMask(cpu_num_to_mask(target_cpu));
}
void Scheduler::Unblock(WaitQueueSublist list) {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_unblock_list"_stringref};
DEBUG_ASSERT(thread_lock.IsHeld());
const SchedTime now = CurrentTime();
cpu_mask_t cpus_to_reschedule_mask = 0;
Thread* thread;
while ((thread = list.pop_back()) != nullptr) {
thread->canary().Assert();
DEBUG_ASSERT(!thread->IsIdle());
SCHED_LTRACEF("thread=%s now=%" PRId64 "\n", thread->name(), now.raw_value());
const cpu_num_t target_cpu = FindTargetCpu(thread);
Scheduler* const target = Get(target_cpu);
thread->set_ready();
target->Insert(now, thread);
cpus_to_reschedule_mask |= cpu_num_to_mask(target_cpu);
}
trace.End();
RescheduleMask(cpus_to_reschedule_mask);
}
void Scheduler::UnblockIdle(Thread* thread) {
DEBUG_ASSERT(thread_lock.IsHeld());
SchedulerState* const state = &thread->scheduler_state();
DEBUG_ASSERT(thread->IsIdle());
DEBUG_ASSERT(state->hard_affinity_ && (state->hard_affinity_ & (state->hard_affinity_ - 1)) == 0);
SCHED_LTRACEF("thread=%s now=%" PRId64 "\n", thread->name(), current_time());
thread->set_ready();
state->curr_cpu_ = lowest_cpu_set(state->hard_affinity_);
}
void Scheduler::Yield() {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_yield"_stringref};
DEBUG_ASSERT(thread_lock.IsHeld());
Thread* const current_thread = Thread::Current::Get();
SchedulerState* const current_state = &current_thread->scheduler_state();
DEBUG_ASSERT(!current_thread->IsIdle());
Scheduler* const current = Get();
const SchedTime now = CurrentTime();
SCHED_LTRACEF("current=%s now=%" PRId64 "\n", current_thread->name(), now.raw_value());
// Set the time slice to expire now.
current_thread->set_ready();
current_state->time_slice_ns_ = now - current->start_of_current_time_slice_ns_;
DEBUG_ASSERT(current_state->time_slice_ns_ >= 0);
if (IsFairThread(current_thread)) {
// Update the virtual timeline in preparation for snapping the thread's
// virtual finish time to the current virtual time.
current->UpdateTimeline(now);
// The thread is re-evaluated with zero lag against other competing threads
// and may skip lower priority threads with similar arrival times.
current_state->finish_time_ = current->virtual_time_;
current_state->fair_.initial_time_slice_ns = current_state->time_slice_ns_;
current_state->fair_.normalized_timeslice_remainder = SchedRemainder{1};
}
current->RescheduleCommon(now, trace.Completer());
}
void Scheduler::Preempt() {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_preempt"_stringref};
DEBUG_ASSERT(thread_lock.IsHeld());
Thread* const current_thread = Thread::Current::Get();
SchedulerState* const current_state = &current_thread->scheduler_state();
const cpu_num_t current_cpu = arch_curr_cpu_num();
DEBUG_ASSERT(current_state->curr_cpu_ == current_cpu);
DEBUG_ASSERT(current_state->last_cpu_ == current_state->curr_cpu_);
const SchedTime now = CurrentTime();
SCHED_LTRACEF("current=%s now=%" PRId64 "\n", current_thread->name(), now.raw_value());
current_thread->set_ready();
Get()->RescheduleCommon(now, trace.Completer());
}
void Scheduler::Reschedule() {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_reschedule"_stringref};
DEBUG_ASSERT(thread_lock.IsHeld());
Thread* const current_thread = Thread::Current::Get();
SchedulerState* const current_state = &current_thread->scheduler_state();
const cpu_num_t current_cpu = arch_curr_cpu_num();
// Pend the preemption rather than rescheduling if preemption is disabled or
// if there is more than one spinlock held.
// TODO(fxbug.dev/64884): Remove check when spinlocks imply preempt disable.
if (!current_thread->preemption_state().PreemptIsEnabled() || arch_num_spinlocks_held() > 1 ||
arch_blocking_disallowed()) {
current_thread->preemption_state().preempts_pending_ |= cpu_num_to_mask(current_cpu);
return;
}
DEBUG_ASSERT(current_state->curr_cpu_ == current_cpu);
DEBUG_ASSERT(current_state->last_cpu_ == current_state->curr_cpu_);
const SchedTime now = CurrentTime();
SCHED_LTRACEF("current=%s now=%" PRId64 "\n", current_thread->name(), now.raw_value());
current_thread->set_ready();
Get()->RescheduleCommon(now, trace.Completer());
}
void Scheduler::RescheduleInternal() {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_resched_internal"_stringref};
Get()->RescheduleCommon(CurrentTime(), trace.Completer());
}
void Scheduler::Migrate(Thread* thread) {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_migrate"_stringref};
DEBUG_ASSERT(thread_lock.IsHeld());
SchedulerState* const state = &thread->scheduler_state();
const cpu_mask_t effective_cpu_mask = state->GetEffectiveCpuMask(mp_get_active_mask());
const cpu_mask_t curr_cpu_mask = cpu_num_to_mask(state->curr_cpu_);
const cpu_mask_t next_cpu_mask = cpu_num_to_mask(state->next_cpu_);
const bool stale_curr_cpu = (curr_cpu_mask & effective_cpu_mask) == 0;
const bool stale_next_cpu =
state->next_cpu_ != INVALID_CPU && (next_cpu_mask & effective_cpu_mask) == 0;
// Clear the next CPU if it is no longer in the effective CPU mask. A new value will be
// determined, if necessary.
if (stale_next_cpu) {
state->next_cpu_ = INVALID_CPU;
}
cpu_mask_t cpus_to_reschedule_mask = 0;
if (thread->state() == THREAD_RUNNING && stale_curr_cpu) {
// The CPU the thread is running on will take care of the actual migration.
cpus_to_reschedule_mask |= curr_cpu_mask;
} else if (thread->state() == THREAD_READY && (stale_curr_cpu || stale_next_cpu)) {
Scheduler* current = Get(state->curr_cpu_);
const cpu_num_t target_cpu = FindTargetCpu(thread);
// If the thread has a migration function it will stay on the same CPU until the migration
// function is called there. Otherwise, the migration is handled here.
if (target_cpu != state->curr_cpu()) {
DEBUG_ASSERT(state->InQueue());
current->GetRunQueue(thread).erase(*thread);
current->Remove(thread);
Scheduler* const target = Get(target_cpu);
target->Insert(CurrentTime(), thread);
// Reschedule both CPUs to handle the run queue changes.
cpus_to_reschedule_mask |= cpu_num_to_mask(target_cpu) | curr_cpu_mask;
}
}
trace.End();
RescheduleMask(cpus_to_reschedule_mask);
}
void Scheduler::MigrateUnpinnedThreads() {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_migrate_unpinned"_stringref};
DEBUG_ASSERT(thread_lock.IsHeld());
const cpu_num_t current_cpu = arch_curr_cpu_num();
const cpu_mask_t current_cpu_mask = cpu_num_to_mask(current_cpu);
// Prevent this CPU from being selected as a target for scheduling threads.
mp_set_curr_cpu_active(false);
const SchedTime now = CurrentTime();
Scheduler* const current = Get(current_cpu);
RunQueue pinned_threads;
cpu_mask_t cpus_to_reschedule_mask = 0;
while (!current->fair_run_queue_.is_empty()) {
Thread* const thread = current->fair_run_queue_.pop_front();
if (thread->scheduler_state().hard_affinity_ == current_cpu_mask) {
// Keep track of threads pinned to this CPU.
pinned_threads.insert(thread);
} else {
// Move unpinned threads to another available CPU.
current->TraceThreadQueueEvent("tqe_deque_migrate_unpinned_fair"_stringref, thread);
current->Remove(thread);
thread->CallMigrateFnLocked(Thread::MigrateStage::Before);
thread->scheduler_state().next_cpu_ = INVALID_CPU;
const cpu_num_t target_cpu = FindTargetCpu(thread);
Scheduler* const target = Get(target_cpu);
DEBUG_ASSERT(target != current);
target->Insert(now, thread);
cpus_to_reschedule_mask |= cpu_num_to_mask(target_cpu);
}
}
// Return the pinned threads to the fair run queue.
current->fair_run_queue_ = ktl::move(pinned_threads);
while (!current->deadline_run_queue_.is_empty()) {
Thread* const thread = current->deadline_run_queue_.pop_front();
if (thread->scheduler_state().hard_affinity_ == current_cpu_mask) {
// Keep track of threads pinned to this CPU.
pinned_threads.insert(thread);
} else {
// Move unpinned threads to another available CPU.
current->TraceThreadQueueEvent("tqe_deque_migrate_unpinned_deadline"_stringref, thread);
current->Remove(thread);
thread->CallMigrateFnLocked(Thread::MigrateStage::Before);
thread->scheduler_state().next_cpu_ = INVALID_CPU;
const cpu_num_t target_cpu = FindTargetCpu(thread);
Scheduler* const target = Get(target_cpu);
DEBUG_ASSERT(target != current);
target->Insert(now, thread);
cpus_to_reschedule_mask |= cpu_num_to_mask(target_cpu);
}
}
// Return the pinned threads to the deadline run queue.
current->deadline_run_queue_ = ktl::move(pinned_threads);
// Call all migrate functions for threads last run on the current CPU.
Thread::CallMigrateFnForCpuLocked(current_cpu);
trace.End();
RescheduleMask(cpus_to_reschedule_mask);
}
void Scheduler::UpdateWeightCommon(Thread* thread, int original_priority, SchedWeight weight,
cpu_mask_t* cpus_to_reschedule_mask, PropagatePI propagate) {
SchedulerState* const state = &thread->scheduler_state();
switch (thread->state()) {
case THREAD_INITIAL:
case THREAD_SLEEPING:
case THREAD_SUSPENDED:
// Adjust the weight of the thread so that the correct value is
// available when the thread enters the run queue.
state->discipline_ = SchedDiscipline::Fair;
state->fair_.weight = weight;
break;
case THREAD_RUNNING:
case THREAD_READY: {
DEBUG_ASSERT(is_valid_cpu_num(state->curr_cpu_));
Scheduler* const current = Get(state->curr_cpu_);
// If the thread is in a run queue, remove it before making subsequent
// changes to the properties of the thread. Erasing and enqueuing depend
// on having the current discipline set before hand.
if (thread->state() == THREAD_READY) {
DEBUG_ASSERT(state->InQueue());
DEBUG_ASSERT(state->active());
current->GetRunQueue(thread).erase(*thread);
current->TraceThreadQueueEvent("tqe_deque_update_weight"_stringref, thread);
}
if (IsDeadlineThread(thread)) {
// Changed to the fair discipline and update the task counts. Changing
// from deadline to fair behaves similarly to a yield.
current->UpdateTotalDeadlineUtilization(-state->deadline_.utilization);
state->discipline_ = SchedDiscipline::Fair;
state->start_time_ = current->virtual_time_;
state->finish_time_ = current->virtual_time_;
state->time_slice_ns_ = SchedDuration{0};
state->fair_.initial_time_slice_ns = SchedDuration{0};
state->fair_.normalized_timeslice_remainder = SchedRemainder{1};
current->runnable_deadline_task_count_--;
current->runnable_fair_task_count_++;
} else {
// Remove the old weight from the run queue.
current->weight_total_ -= state->fair_.weight;
}
// Update the weight of the thread and the run queue. The time slice
// of a running thread will be adjusted during reschedule due to the
// change in demand on the run queue.
current->weight_total_ += weight;
state->fair_.weight = weight;
// Adjust the position of the thread in the run queue based on the new
// weight.
if (thread->state() == THREAD_READY) {
current->QueueThread(thread, Placement::Adjustment);
}
*cpus_to_reschedule_mask |= cpu_num_to_mask(state->curr_cpu_);
break;
}
case THREAD_BLOCKED:
case THREAD_BLOCKED_READ_LOCK:
// Update the weight of the thread blocked in a wait queue. Also
// handle the race where the thread is no longer in the wait queue
// but has not yet transitioned to ready.
state->discipline_ = SchedDiscipline::Fair;
state->fair_.weight = weight;
thread->wait_queue_state().UpdatePriorityIfBlocked(thread, original_priority, propagate);
break;
default:
break;
}
}
void Scheduler::UpdateDeadlineCommon(Thread* thread, int original_priority,
const SchedDeadlineParams& params,
cpu_mask_t* cpus_to_reschedule_mask, PropagatePI propagate) {
SchedulerState* const state = &thread->scheduler_state();
switch (thread->state()) {
case THREAD_INITIAL:
case THREAD_SLEEPING:
case THREAD_SUSPENDED:
// Adjust the deadline of the thread so that the correct value is
// available when the thread enters the run queue.
state->discipline_ = SchedDiscipline::Deadline;
state->deadline_ = params;
break;
case THREAD_RUNNING:
case THREAD_READY: {
DEBUG_ASSERT(is_valid_cpu_num(state->curr_cpu_));
Scheduler* const current = Get(state->curr_cpu_);
// If the thread is running or is already a deadline task, keep the
// original arrival time. Otherwise, when moving a ready task from the
// fair run queue to the deadline run queue, use the current time as the
// arrival time.
SchedTime effective_start_time;
if (IsDeadlineThread(thread)) {
effective_start_time = state->start_time_;
} else if (thread->state() == THREAD_RUNNING) {
effective_start_time = current->start_of_current_time_slice_ns_;
} else {
effective_start_time = CurrentTime();
}
// If the thread is in a run queue, remove it before making subsequent
// changes to the properties of the thread. Erasing and enqueuing depend
// on having the correct discipline set before hand.
if (thread->state() == THREAD_READY) {
DEBUG_ASSERT(state->InQueue());
DEBUG_ASSERT(state->active());
current->GetRunQueue(thread).erase(*thread);
}
if (IsFairThread(thread)) {
// Changed to the deadline discipline and update the task counts and
// queue weight.
current->weight_total_ -= state->fair_.weight;
state->discipline_ = SchedDiscipline::Deadline;
current->runnable_fair_task_count_--;
current->runnable_deadline_task_count_++;
} else {
// Remove the old utilization from the run queue. Wait to update the
// exported value until the new value is added below.
current->total_deadline_utilization_ -= state->deadline_.utilization;
DEBUG_ASSERT(current->total_deadline_utilization_ >= 0);
}
// Update the deadline params and the run queue.
state->deadline_ = params;
state->start_time_ = effective_start_time;
state->finish_time_ = state->start_time_ + params.deadline_ns;
state->time_slice_ns_ = ktl::min(state->time_slice_ns_, params.capacity_ns);
current->UpdateTotalDeadlineUtilization(state->deadline_.utilization);
// The target preemption time orignially set when the thread was fair
// scheduled does not account for the performance scale applied to the
// time slice when computing the preemption time for a deadline scheduled
// thread. There is an assertion that the time slice is expired by the
// time the target preemption time is reached. Correct the value to avoid
// failing the consistency check.
if (thread->state() == THREAD_RUNNING) {
const SchedDuration scaled_time_slice_ns = current->ScaleUp(state->time_slice_ns_);
current->target_preemption_time_ns_ = ktl::min<SchedTime>(
current->start_of_current_time_slice_ns_ + scaled_time_slice_ns, state->finish_time_);
}
// Adjust the position of the thread in the run queue based on the new
// deadline.
if (thread->state() == THREAD_READY) {
current->QueueThread(thread, Placement::Adjustment);
}
*cpus_to_reschedule_mask |= cpu_num_to_mask(state->curr_cpu_);
break;
}
case THREAD_BLOCKED:
case THREAD_BLOCKED_READ_LOCK:
// Update the weight of the thread blocked in a wait queue. Also
// handle the race where the thread is no longer in the wait queue
// but has not yet transitioned to ready.
state->discipline_ = SchedDiscipline::Deadline;
state->deadline_ = params;
thread->wait_queue_state().UpdatePriorityIfBlocked(thread, original_priority, propagate);
break;
default:
break;
}
}
void Scheduler::ChangeWeight(Thread* thread, int priority, cpu_mask_t* cpus_to_reschedule_mask) {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_change_weight"_stringref};
SchedulerState* const state = &thread->scheduler_state();
DEBUG_ASSERT(thread_lock.IsHeld());
SCHED_LTRACEF("thread={%s, %s} base=%d effective=%d inherited=%d\n", thread->name(),
ToString(thread->state()), state->base_priority_, state->effective_priority_,
state->inherited_priority_);
if (thread->IsIdle() || thread->state() == THREAD_DEATH) {
return;
}
// TODO(eieio): The rest of the kernel still uses priority so we have to
// operate in those terms here. Abstract the notion of priority once the
// deadline scheduler is available and remove this conversion once the
// kernel uses the abstraction throughout.
const int original_priority = state->effective_priority_;
state->base_priority_ = priority;
state->effective_priority_ = ktl::max(state->base_priority_, state->inherited_priority_);
// Perform the state-specific updates if the discipline or effective priority
// changed.
if (IsDeadlineThread(thread) || state->effective_priority_ != original_priority) {
UpdateWeightCommon(thread, original_priority, PriorityToWeight(state->effective_priority_),
cpus_to_reschedule_mask, PropagatePI::Yes);
}
trace.End(original_priority, state->effective_priority_);
}
void Scheduler::ChangeDeadline(Thread* thread, const SchedDeadlineParams& params,
cpu_mask_t* cpus_to_reschedule_mask) {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_change_deadline"_stringref};
SchedulerState* const state = &thread->scheduler_state();
DEBUG_ASSERT(thread_lock.IsHeld());
SCHED_LTRACEF("thread={%s, %s} base=%d effective=%d inherited=%d\n", thread->name(),
ToString(thread->state()), state->base_priority_, state->effective_priority_,
state->inherited_priority_);
if (thread->IsIdle() || thread->state() == THREAD_DEATH) {
return;
}
const bool changed = IsFairThread(thread) || state->deadline_ != params;
// Always set deadline threads to the highest fair priority. This is a
// workaround until deadline priority inheritance is worked out.
// TODO(eieio): Replace this with actual deadline PI.
const int original_priority = state->effective_priority_;
state->base_priority_ = HIGHEST_PRIORITY;
state->inherited_priority_ = -1;
state->effective_priority_ = state->base_priority_;
// Perform the state-specific updates if the discipline or deadline params changed.
if (changed) {
UpdateDeadlineCommon(thread, original_priority, params, cpus_to_reschedule_mask,
PropagatePI::Yes);
}
trace.End(original_priority, state->effective_priority_);
}
void Scheduler::InheritWeight(Thread* thread, int priority, cpu_mask_t* cpus_to_reschedule_mask) {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_inherit_weight"_stringref};
SchedulerState* const state = &thread->scheduler_state();
DEBUG_ASSERT(thread_lock.IsHeld());
SCHED_LTRACEF("thread={%s, %s} base=%d effective=%d inherited=%d\n", thread->name(),
ToString(thread->state()), state->base_priority_, state->effective_priority_,
state->inherited_priority_);
// For now deadline threads are logically max weight for the purposes of
// priority inheritance.
if (IsDeadlineThread(thread)) {
return;
}
const int original_priority = state->effective_priority_;
state->inherited_priority_ = priority;
state->effective_priority_ = ktl::max(state->base_priority_, state->inherited_priority_);
// Perform the state-specific updates if the effective priority changed.
if (state->effective_priority_ != original_priority) {
UpdateWeightCommon(thread, original_priority, PriorityToWeight(state->effective_priority_),
cpus_to_reschedule_mask, PropagatePI::No);
}
trace.End(original_priority, state->effective_priority_);
}
void Scheduler::TimerTick(SchedTime now) {
LocalTraceDuration<KTRACE_COMMON> trace{"sched_timer_tick"_stringref};
Thread::Current::preemption_state().PreemptSetPending();
}
void Scheduler::InheritPriority(Thread* thread, int priority) {
cpu_mask_t cpus_to_reschedule_mask = 0;
InheritWeight(thread, priority, &cpus_to_reschedule_mask);
RescheduleMask(cpus_to_reschedule_mask);
}
void Scheduler::ChangePriority(Thread* thread, int priority) {
cpu_mask_t cpus_to_reschedule_mask = 0;
ChangeWeight(thread, priority, &cpus_to_reschedule_mask);
RescheduleMask(cpus_to_reschedule_mask);
}
void Scheduler::ChangeDeadline(Thread* thread, const zx_sched_deadline_params_t& params) {
cpu_mask_t cpus_to_reschedule_mask = 0;
ChangeDeadline(thread, params, &cpus_to_reschedule_mask);
RescheduleMask(cpus_to_reschedule_mask);
}
zx_time_t Scheduler::GetTargetPreemptionTime() {
DEBUG_ASSERT(Thread::Current::preemption_state().PreemptDisableCount() > 0);
Scheduler* const current = Get();
Guard<MonitoredSpinLock, IrqSave> guard{ThreadLock::Get(), SOURCE_TAG};
return current->target_preemption_time_ns_.raw_value();
}