| commit | 62ce712ecc887f669610a93efe18abecf70b47a0 | [log] [tgz] |
|---|---|---|
| author | Abseil Team <absl-team@google.com> | Fri Jan 08 09:10:22 2021 -0800 |
| committer | Derek Mauro <dmauro@google.com> | Fri Jan 08 12:50:29 2021 -0500 |
| tree | 21ef34fc27e09d5ff51baad57d27b9ec033f9388 | |
| parent | 92ba53599931fcbe31e7970497cb9e60091434c1 [diff] |
Export of internal Abseil changes -- b927776da818c674a674e46a7bbbdd54170a0ad3 by Todd Lipcon <tlipcon@google.com>: Include priority in the calculation of mutex waiter equivalence This changes the behavior of the absl::Mutex wait list to take into account waiter priority when creating "skip chains". A skip chain on the wait list is a set of adjacent waiters that share some property and enable skipping during traversal. Prior to this CL, the skip chains were formed of waiters with the same wait type (e.g. exclusive vs read) and Condition. With this CL, the priority is also taken into account. This avoids O(n) behavior when enqueueing a waiter onto a wait list where the oldest waiter is at a lower priority than the waiter to be enqueued. With the prior notion of equivalence class, a skip chain could contain waiters of different priority, so we had to walk the linked list one-by-one until finding the appropriate insertion point. With the new equivalence class computation, we can skip past all of the equivalent waiters to find the right insertion point. This gives a substantial improvement to the enqueue performance in the case where there's already a waiter at lower priority. Note that even though this code path isn't a hot one, it's performed while holding the Mutex's spinlock, which prevents other threads from unlocking the Mutex, so minimizing the time under the critical section can have "knock-on" throughput benefits. Notable performance differences: name old cpu/op new cpu/op delta BM_MutexEnqueue/multiple_priorities:0/threads:4 8.60µs ± 7% 8.69µs ± 6% ~ (p=0.365 n=19+20) BM_MutexEnqueue/multiple_priorities:0/threads:64 8.47µs ± 5% 8.64µs ±10% ~ (p=0.569 n=19+20) BM_MutexEnqueue/multiple_priorities:0/threads:128 8.56µs ± 3% 8.55µs ± 6% ~ (p=0.563 n=17+17) BM_MutexEnqueue/multiple_priorities:0/threads:512 8.98µs ± 8% 8.86µs ± 4% ~ (p=0.232 n=19+17) BM_MutexEnqueue/multiple_priorities:1/threads:4 6.64µs ±10% 6.45µs ± 4% ~ (p=0.097 n=20+17) BM_MutexEnqueue/multiple_priorities:1/threads:64 15.2µs ± 8% 9.1µs ± 4% -39.93% (p=0.000 n=20+17) BM_MutexEnqueue/multiple_priorities:1/threads:128 22.3µs ± 6% 9.4µs ± 4% -57.82% (p=0.000 n=20+17) BM_MutexEnqueue/multiple_priorities:1/threads:512 61.5µs ± 3% 10.1µs ± 8% -83.53% (p=0.000 n=20+20) name old time/op new time/op delta BM_Mutex/real_time/threads:1 19.6ns ± 4% 19.8ns ±11% ~ (p=0.534 n=17+17) BM_Mutex/real_time/threads:112 120ns ±17% 122ns ±14% ~ (p=0.988 n=20+18) BM_MutexEnqueue/multiple_priorities:0/threads:4 5.18µs ± 6% 5.23µs ± 6% ~ (p=0.428 n=19+20) BM_MutexEnqueue/multiple_priorities:0/threads:64 5.06µs ± 5% 5.18µs ±10% ~ (p=0.235 n=19+20) BM_MutexEnqueue/multiple_priorities:0/threads:128 5.16µs ± 3% 5.14µs ± 6% ~ (p=0.474 n=17+17) BM_MutexEnqueue/multiple_priorities:0/threads:512 5.40µs ± 8% 5.32µs ± 5% ~ (p=0.196 n=20+18) BM_MutexEnqueue/multiple_priorities:1/threads:4 3.99µs ±10% 3.88µs ± 3% ~ (p=0.074 n=20+17) BM_MutexEnqueue/multiple_priorities:1/threads:64 8.48µs ± 9% 5.41µs ± 3% -36.20% (p=0.000 n=20+16) BM_MutexEnqueue/multiple_priorities:1/threads:128 12.2µs ± 6% 5.6µs ± 4% -54.43% (p=0.000 n=20+17) BM_MutexEnqueue/multiple_priorities:1/threads:512 32.1µs ± 3% 5.9µs ± 8% -81.45% (p=0.000 n=20+20) ... BM_Contended<absl::Mutex>/cs_ns:2000/num_prios:2/real_time/threads:32 1.69µs ± 4% 1.66µs ± 2% -1.91% (p=0.000 n=20+20) BM_Contended<absl::Mutex>/cs_ns:2000/num_prios:2/real_time/threads:48 1.90µs ± 2% 1.82µs ± 2% -4.09% (p=0.000 n=20+19) BM_Contended<absl::Mutex>/cs_ns:2000/num_prios:2/real_time/threads:64 2.19µs ± 2% 1.80µs ± 1% -17.89% (p=0.000 n=20+20) BM_Contended<absl::Mutex>/cs_ns:2000/num_prios:2/real_time/threads:96 2.18µs ± 5% 1.81µs ± 1% -16.94% (p=0.000 n=17+19) BM_Contended<absl::Mutex>/cs_ns:2000/num_prios:2/real_time/threads:128 2.18µs ± 1% 1.91µs ± 2% -12.33% (p=0.000 n=19+20) BM_Contended<absl::Mutex>/cs_ns:2000/num_prios:2/real_time/threads:192 2.27µs ± 2% 1.89µs ± 1% -16.79% (p=0.000 n=20+19) BM_Contended<absl::Mutex>/cs_ns:2000/num_prios:2/real_time/threads:256 2.36µs ± 2% 1.83µs ± 1% -22.25% (p=0.000 n=20+19) PiperOrigin-RevId: 350775432 -- e7812590e5dbd75d21e2e8762713bd04c0353ef6 by Todd Lipcon <tlipcon@google.com>: Fix test timeouts for sequence_lock_test on TSAN PiperOrigin-RevId: 350680903 -- 3090d8154d875f3eabce48876321ae8d6a197302 by Todd Lipcon <tlipcon@google.com>: Add benchmarks for Mutex performance with multiple priorities This adds a new benchmark to mutex_benchmark which forces threads to go through the slow "Enqueue" path. The benchmark runs with varying numbers of threads and with/without the presence of a lower-priority waiter. PiperOrigin-RevId: 350655403 GitOrigin-RevId: b927776da818c674a674e46a7bbbdd54170a0ad3 Change-Id: If739e5e205f0d3867661a52466b8f64e7e033b22
The repository contains the Abseil C++ library code. Abseil is an open-source collection of C++ code (compliant to C++11) designed to augment the C++ standard library.
Abseil is an open-source collection of C++ library code designed to augment the C++ standard library. The Abseil library code is collected from Google's own C++ code base, has been extensively tested and used in production, and is the same code we depend on in our daily coding lives.
In some cases, Abseil provides pieces missing from the C++ standard; in others, Abseil provides alternatives to the standard for special needs we've found through usage in the Google code base. We denote those cases clearly within the library code we provide you.
Abseil is not meant to be a competitor to the standard library; we've just found that many of these utilities serve a purpose within our code base, and we now want to provide those resources to the C++ community as a whole.
If you want to just get started, make sure you at least run through the Abseil Quickstart. The Quickstart contains information about setting up your development environment, downloading the Abseil code, running tests, and getting a simple binary working.
Bazel and CMake are the official build systems for Abseil.
See the quickstart for more information on building Abseil using the Bazel build system.
If you require CMake support, please check the CMake build instructions and CMake Quickstart.
Abseil is officially supported on many platforms. See the Abseil platform support guide for details on supported operating systems, compilers, CPUs, etc.
Abseil contains the following C++ library components:
base Abseil Fundamentals base library contains initialization code and other code which all other Abseil code depends on. Code within base may not depend on any other code (other than the C++ standard library).algorithm algorithm library contains additions to the C++ <algorithm> library and container-based versions of such algorithms.container container library contains additional STL-style containers, including Abseil's unordered “Swiss table” containers.debugging debugging library contains code useful for enabling leak checks, and stacktrace and symbolization utilities.hash hash library contains the hashing framework and default hash functor implementations for hashable types in Abseil.memory memory library contains C++11-compatible versions of std::make_unique() and related memory management facilities.meta meta library contains C++11-compatible versions of type checks available within C++14 and C++17 versions of the C++ <type_traits> library.numeric numeric library contains C++11-compatible 128-bit integers.status status contains abstractions for error handling, specifically absl::Status and absl::StatusOr<T>.strings strings library contains a variety of strings routines and utilities, including a C++11-compatible version of the C++17 std::string_view type.synchronization synchronization library contains concurrency primitives (Abseil's absl::Mutex class, an alternative to std::mutex) and a variety of synchronization abstractions.time time library contains abstractions for computing with absolute points in time, durations of time, and formatting and parsing time within time zones.types types library contains non-container utility types, like a C++11-compatible version of the C++17 std::optional type.utility utility library contains utility and helper code.Abseil recommends users “live-at-head” (update to the latest commit from the master branch as often as possible). However, we realize this philosophy doesn't work for every project, so we also provide Long Term Support Releases to which we backport fixes for severe bugs. See our release management document for more details.
The Abseil C++ library is licensed under the terms of the Apache license. See LICENSE for more information.
For more information about Abseil: