src/tests/microbenchmarks/context_switch_overhead_helper.cc

// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <lib/fdio/spawn.h>
#include <lib/syslog/cpp/macros.h>
#include <lib/zx/eventpair.h>
#include <lib/zx/handle.h>
#include <lib/zx/job.h>
#include <lib/zx/process.h>
#include <lib/zx/time.h>
#include <pthread.h>
#include <zircon/assert.h>
#include <zircon/processargs.h>
#include <zircon/syscalls.h>

#include <thread>

struct State {
  pthread_barrier_t start_barrier;
  pthread_barrier_t stop_barrier;
  const size_t number_of_switches;

  State(size_t thread_count, size_t number_of_switches) : number_of_switches(number_of_switches) {
    FX_CHECK(0 == pthread_barrier_init(&start_barrier, nullptr,
                                       thread_count + 1));  // additional thread for main
    FX_CHECK(0 == pthread_barrier_init(&stop_barrier, nullptr,
                                       thread_count + 1));  // additional thread for main
  }
};

void ThreadPair(State* state) {
  auto thread_action = [state](zx::eventpair event, bool first) {
    auto wait_val = pthread_barrier_wait(&state->start_barrier);
    FX_CHECK(wait_val == PTHREAD_BARRIER_SERIAL_THREAD || wait_val == 0);

    size_t to_receive = state->number_of_switches;

    if (first) {
      FX_CHECK(ZX_OK == event.signal_peer(0, ZX_USER_SIGNAL_0));
    }

    while (to_receive > 0) {
      FX_CHECK(ZX_OK == event.wait_one(ZX_USER_SIGNAL_0, zx::time::infinite(), nullptr));
      to_receive--;
      FX_CHECK(ZX_OK == event.signal(ZX_USER_SIGNAL_0, 0));
      FX_CHECK(ZX_OK == event.signal_peer(0, ZX_USER_SIGNAL_0));
    }

    wait_val = pthread_barrier_wait(&state->stop_barrier);
    FX_CHECK(wait_val == PTHREAD_BARRIER_SERIAL_THREAD || wait_val == 0);
  };

  zx::eventpair e1, e2;
  FX_CHECK(ZX_OK == zx::eventpair::create(0, &e1, &e2));

  std::thread(thread_action, std::move(e1), true).detach();
  std::thread(thread_action, std::move(e2), false).detach();
}

const char kMessage[] = "ping";
const size_t kMessageSize = 4;

int main(int argc, char** argv) {
  zx::channel incoming(zx_take_startup_handle(PA_USER0));

  if (!incoming) {
    printf("ERROR: Invalid incoming handle\n");
    return 1;
  }

  size_t cpus = zx_system_get_num_cpus();
  uint64_t number_of_switches = 0;

  // Signal that this process is ready to accept instructions.
  FX_CHECK(ZX_OK == incoming.write(0, kMessage, kMessageSize, nullptr, 0));

  while (true) {
    // Read the number of context switches to perform.
    FX_CHECK(ZX_OK == incoming.wait_one(ZX_CHANNEL_READABLE, zx::time::infinite(), nullptr));
    if (ZX_OK != incoming.read(0, &number_of_switches, nullptr, sizeof(number_of_switches), 0,
                               nullptr, nullptr)) {
      break;
    }
    State state(cpus * 2, number_of_switches);

    // Initialize all thread pairs with the state.
    for (size_t i = 0; i < cpus; i++) {
      ThreadPair(&state);
    }

    // Wait until all threads are ready to start, then signal to the test that we have started.
    auto wait_val = pthread_barrier_wait(&state.start_barrier);
    FX_CHECK(wait_val == PTHREAD_BARRIER_SERIAL_THREAD || wait_val == 0);
    FX_CHECK(ZX_OK == incoming.write(0, kMessage, kMessageSize, nullptr, 0));

    // Wait until all threads have completed, then signal to the test that we have finished.
    wait_val = pthread_barrier_wait(&state.stop_barrier);
    FX_CHECK(wait_val == PTHREAD_BARRIER_SERIAL_THREAD || wait_val == 0);
    FX_CHECK(ZX_OK == incoming.write(0, kMessage, kMessageSize, nullptr, 0));
  }

  return 0;
}