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090c78a0d7
Summary: Background activities like compaction can negatively affect latency of higher-priority tasks like request processing. To avoid this, rocksdb already lowers the IO priority of background threads on Linux systems. While this takes care of typical IO-bound systems, it does not help much when CPU (temporarily) becomes the bottleneck. This is especially likely when using more expensive compression settings. This patch adds an API to allow for lowering the CPU priority of background threads, modeled on the IO priority API. Benchmarks (see below) show significant latency and throughput improvements when CPU bound. As a result, workloads with some CPU usage bursts should benefit from lower latencies at a given utilization, or should be able to push utilization higher at a given request latency target. A useful side effect is that compaction CPU usage is now easily visible in common tools, allowing for an easier estimation of the contribution of compaction vs. request processing threads. As with IO priority, the implementation is limited to Linux, degrading to a no-op on other systems. Closes https://github.com/facebook/rocksdb/pull/3763 Differential Revision: D7740096 Pulled By: gwicke fbshipit-source-id: e5d32373e8dc403a7b0c2227023f9ce4f22b413c
114 lines
3.6 KiB
C++
114 lines
3.6 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once
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#include "rocksdb/threadpool.h"
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#include "rocksdb/env.h"
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#include <memory>
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#include <functional>
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namespace rocksdb {
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class ThreadPoolImpl : public ThreadPool {
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public:
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ThreadPoolImpl();
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~ThreadPoolImpl();
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ThreadPoolImpl(ThreadPoolImpl&&) = delete;
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ThreadPoolImpl& operator=(ThreadPoolImpl&&) = delete;
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// Implement ThreadPool interfaces
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// Wait for all threads to finish.
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// Discards all the jobs that did not
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// start executing and waits for those running
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// to complete
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void JoinAllThreads() override;
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// Set the number of background threads that will be executing the
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// scheduled jobs.
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void SetBackgroundThreads(int num) override;
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int GetBackgroundThreads() override;
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// Get the number of jobs scheduled in the ThreadPool queue.
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unsigned int GetQueueLen() const override;
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// Waits for all jobs to complete those
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// that already started running and those that did not
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// start yet
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void WaitForJobsAndJoinAllThreads() override;
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// Make threads to run at a lower kernel IO priority
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// Currently only has effect on Linux
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void LowerIOPriority();
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// Make threads to run at a lower kernel CPU priority
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// Currently only has effect on Linux
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void LowerCPUPriority();
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// Ensure there is at aleast num threads in the pool
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// but do not kill threads if there are more
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void IncBackgroundThreadsIfNeeded(int num);
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// Submit a fire and forget job
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// These jobs can not be unscheduled
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// This allows to submit the same job multiple times
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void SubmitJob(const std::function<void()>&) override;
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// This moves the function in for efficiency
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void SubmitJob(std::function<void()>&&) override;
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// Schedule a job with an unschedule tag and unschedule function
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// Can be used to filter and unschedule jobs by a tag
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// that are still in the queue and did not start running
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void Schedule(void (*function)(void* arg1), void* arg, void* tag,
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void (*unschedFunction)(void* arg));
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// Filter jobs that are still in a queue and match
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// the given tag. Remove them from a queue if any
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// and for each such job execute an unschedule function
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// if such was given at scheduling time.
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int UnSchedule(void* tag);
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void SetHostEnv(Env* env);
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Env* GetHostEnv() const;
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// Return the thread priority.
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// This would allow its member-thread to know its priority.
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Env::Priority GetThreadPriority() const;
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// Set the thread priority.
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void SetThreadPriority(Env::Priority priority);
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static void PthreadCall(const char* label, int result);
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struct Impl;
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private:
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// Current public virtual interface does not provide usable
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// functionality and thus can not be used internally to
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// facade different implementations.
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//
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// We propose a pimpl idiom in order to easily replace the thread pool impl
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// w/o touching the header file but providing a different .cc potentially
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// CMake option driven.
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//
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// Another option is to introduce a Env::MakeThreadPool() virtual interface
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// and override the environment. This would require refactoring ThreadPool usage.
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//
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// We can also combine these two approaches
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std::unique_ptr<Impl> impl_;
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};
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} // namespace rocksdb
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