rocksdb/util/mutexlock.h

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#pragma once
support for concurrent adds to memtable Summary: This diff adds support for concurrent adds to the skiplist memtable implementations. Memory allocation is made thread-safe by the addition of a spinlock, with small per-core buffers to avoid contention. Concurrent memtable writes are made via an additional method and don't impose a performance overhead on the non-concurrent case, so parallelism can be selected on a per-batch basis. Write thread synchronization is an increasing bottleneck for higher levels of concurrency, so this diff adds --enable_write_thread_adaptive_yield (default off). This feature causes threads joining a write batch group to spin for a short time (default 100 usec) using sched_yield, rather than going to sleep on a mutex. If the timing of the yield calls indicates that another thread has actually run during the yield then spinning is avoided. This option improves performance for concurrent situations even without parallel adds, although it has the potential to increase CPU usage (and the heuristic adaptation is not yet mature). Parallel writes are not currently compatible with inplace updates, update callbacks, or delete filtering. Enable it with --allow_concurrent_memtable_write (and --enable_write_thread_adaptive_yield). Parallel memtable writes are performance neutral when there is no actual parallelism, and in my experiments (SSD server-class Linux and varying contention and key sizes for fillrandom) they are always a performance win when there is more than one thread. Statistics are updated earlier in the write path, dropping the number of DB mutex acquisitions from 2 to 1 for almost all cases. This diff was motivated and inspired by Yahoo's cLSM work. It is more conservative than cLSM: RocksDB's write batch group leader role is preserved (along with all of the existing flush and write throttling logic) and concurrent writers are blocked until all memtable insertions have completed and the sequence number has been advanced, to preserve linearizability. My test config is "db_bench -benchmarks=fillrandom -threads=$T -batch_size=1 -memtablerep=skip_list -value_size=100 --num=1000000/$T -level0_slowdown_writes_trigger=9999 -level0_stop_writes_trigger=9999 -disable_auto_compactions --max_write_buffer_number=8 -max_background_flushes=8 --disable_wal --write_buffer_size=160000000 --block_size=16384 --allow_concurrent_memtable_write" on a two-socket Xeon E5-2660 @ 2.2Ghz with lots of memory and an SSD hard drive. With 1 thread I get ~440Kops/sec. Peak performance for 1 socket (numactl -N1) is slightly more than 1Mops/sec, at 16 threads. Peak performance across both sockets happens at 30 threads, and is ~900Kops/sec, although with fewer threads there is less performance loss when the system has background work. Test Plan: 1. concurrent stress tests for InlineSkipList and DynamicBloom 2. make clean; make check 3. make clean; DISABLE_JEMALLOC=1 make valgrind_check; valgrind db_bench 4. make clean; COMPILE_WITH_TSAN=1 make all check; db_bench 5. make clean; COMPILE_WITH_ASAN=1 make all check; db_bench 6. make clean; OPT=-DROCKSDB_LITE make check 7. verify no perf regressions when disabled Reviewers: igor, sdong Reviewed By: sdong Subscribers: MarkCallaghan, IslamAbdelRahman, anthony, yhchiang, rven, sdong, guyg8, kradhakrishnan, dhruba Differential Revision: https://reviews.facebook.net/D50589
2015-08-15 01:59:07 +02:00
#include <assert.h>
#include <atomic>
#include <mutex>
#include <thread>
#include "port/port.h"
namespace ROCKSDB_NAMESPACE {
// Helper class that locks a mutex on construction and unlocks the mutex when
// the destructor of the MutexLock object is invoked.
//
// Typical usage:
//
// void MyClass::MyMethod() {
// MutexLock l(&mu_); // mu_ is an instance variable
// ... some complex code, possibly with multiple return paths ...
// }
class MutexLock {
public:
explicit MutexLock(port::Mutex *mu) : mu_(mu) {
this->mu_->Lock();
}
// No copying allowed
MutexLock(const MutexLock &) = delete;
void operator=(const MutexLock &) = delete;
~MutexLock() { this->mu_->Unlock(); }
private:
port::Mutex *const mu_;
};
//
// Acquire a ReadLock on the specified RWMutex.
// The Lock will be automatically released then the
// object goes out of scope.
//
class ReadLock {
public:
explicit ReadLock(port::RWMutex *mu) : mu_(mu) {
this->mu_->ReadLock();
}
// No copying allowed
ReadLock(const ReadLock &) = delete;
void operator=(const ReadLock &) = delete;
~ReadLock() { this->mu_->ReadUnlock(); }
private:
port::RWMutex *const mu_;
};
//
// Automatically unlock a locked mutex when the object is destroyed
//
class ReadUnlock {
public:
explicit ReadUnlock(port::RWMutex *mu) : mu_(mu) { mu->AssertHeld(); }
// No copying allowed
ReadUnlock(const ReadUnlock &) = delete;
ReadUnlock &operator=(const ReadUnlock &) = delete;
~ReadUnlock() { mu_->ReadUnlock(); }
private:
port::RWMutex *const mu_;
};
//
// Acquire a WriteLock on the specified RWMutex.
// The Lock will be automatically released then the
// object goes out of scope.
//
class WriteLock {
public:
explicit WriteLock(port::RWMutex *mu) : mu_(mu) {
this->mu_->WriteLock();
}
// No copying allowed
WriteLock(const WriteLock &) = delete;
void operator=(const WriteLock &) = delete;
~WriteLock() { this->mu_->WriteUnlock(); }
private:
port::RWMutex *const mu_;
};
support for concurrent adds to memtable Summary: This diff adds support for concurrent adds to the skiplist memtable implementations. Memory allocation is made thread-safe by the addition of a spinlock, with small per-core buffers to avoid contention. Concurrent memtable writes are made via an additional method and don't impose a performance overhead on the non-concurrent case, so parallelism can be selected on a per-batch basis. Write thread synchronization is an increasing bottleneck for higher levels of concurrency, so this diff adds --enable_write_thread_adaptive_yield (default off). This feature causes threads joining a write batch group to spin for a short time (default 100 usec) using sched_yield, rather than going to sleep on a mutex. If the timing of the yield calls indicates that another thread has actually run during the yield then spinning is avoided. This option improves performance for concurrent situations even without parallel adds, although it has the potential to increase CPU usage (and the heuristic adaptation is not yet mature). Parallel writes are not currently compatible with inplace updates, update callbacks, or delete filtering. Enable it with --allow_concurrent_memtable_write (and --enable_write_thread_adaptive_yield). Parallel memtable writes are performance neutral when there is no actual parallelism, and in my experiments (SSD server-class Linux and varying contention and key sizes for fillrandom) they are always a performance win when there is more than one thread. Statistics are updated earlier in the write path, dropping the number of DB mutex acquisitions from 2 to 1 for almost all cases. This diff was motivated and inspired by Yahoo's cLSM work. It is more conservative than cLSM: RocksDB's write batch group leader role is preserved (along with all of the existing flush and write throttling logic) and concurrent writers are blocked until all memtable insertions have completed and the sequence number has been advanced, to preserve linearizability. My test config is "db_bench -benchmarks=fillrandom -threads=$T -batch_size=1 -memtablerep=skip_list -value_size=100 --num=1000000/$T -level0_slowdown_writes_trigger=9999 -level0_stop_writes_trigger=9999 -disable_auto_compactions --max_write_buffer_number=8 -max_background_flushes=8 --disable_wal --write_buffer_size=160000000 --block_size=16384 --allow_concurrent_memtable_write" on a two-socket Xeon E5-2660 @ 2.2Ghz with lots of memory and an SSD hard drive. With 1 thread I get ~440Kops/sec. Peak performance for 1 socket (numactl -N1) is slightly more than 1Mops/sec, at 16 threads. Peak performance across both sockets happens at 30 threads, and is ~900Kops/sec, although with fewer threads there is less performance loss when the system has background work. Test Plan: 1. concurrent stress tests for InlineSkipList and DynamicBloom 2. make clean; make check 3. make clean; DISABLE_JEMALLOC=1 make valgrind_check; valgrind db_bench 4. make clean; COMPILE_WITH_TSAN=1 make all check; db_bench 5. make clean; COMPILE_WITH_ASAN=1 make all check; db_bench 6. make clean; OPT=-DROCKSDB_LITE make check 7. verify no perf regressions when disabled Reviewers: igor, sdong Reviewed By: sdong Subscribers: MarkCallaghan, IslamAbdelRahman, anthony, yhchiang, rven, sdong, guyg8, kradhakrishnan, dhruba Differential Revision: https://reviews.facebook.net/D50589
2015-08-15 01:59:07 +02:00
//
// SpinMutex has very low overhead for low-contention cases. Method names
// are chosen so you can use std::unique_lock or std::lock_guard with it.
//
class SpinMutex {
public:
SpinMutex() : locked_(false) {}
bool try_lock() {
auto currently_locked = locked_.load(std::memory_order_relaxed);
return !currently_locked &&
locked_.compare_exchange_weak(currently_locked, true,
std::memory_order_acquire,
std::memory_order_relaxed);
}
void lock() {
for (size_t tries = 0;; ++tries) {
if (try_lock()) {
// success
break;
}
port::AsmVolatilePause();
if (tries > 100) {
std::this_thread::yield();
}
}
}
void unlock() { locked_.store(false, std::memory_order_release); }
private:
std::atomic<bool> locked_;
};
// We want to prevent false sharing
template <class T>
struct ALIGN_AS(CACHE_LINE_SIZE) LockData {
T lock_;
};
//
// Inspired by Guava: https://github.com/google/guava/wiki/StripedExplained
// A striped Lock. This offers the underlying lock striping similar
// to that of ConcurrentHashMap in a reusable form, and extends it for
// semaphores and read-write locks. Conceptually, lock striping is the technique
// of dividing a lock into many <i>stripes</i>, increasing the granularity of a
// single lock and allowing independent operations to lock different stripes and
// proceed concurrently, instead of creating contention for a single lock.
//
template <class T, class P>
class Striped {
public:
Striped(size_t stripes, std::function<uint64_t(const P &)> hash)
: stripes_(stripes), hash_(hash) {
locks_ = reinterpret_cast<LockData<T> *>(
port::cacheline_aligned_alloc(sizeof(LockData<T>) * stripes));
for (size_t i = 0; i < stripes; i++) {
new (&locks_[i]) LockData<T>();
}
}
virtual ~Striped() {
if (locks_ != nullptr) {
assert(stripes_ > 0);
for (size_t i = 0; i < stripes_; i++) {
locks_[i].~LockData<T>();
}
port::cacheline_aligned_free(locks_);
}
}
T *get(const P &key) {
uint64_t h = hash_(key);
size_t index = h % stripes_;
return &reinterpret_cast<LockData<T> *>(&locks_[index])->lock_;
}
private:
size_t stripes_;
LockData<T> *locks_;
std::function<uint64_t(const P &)> hash_;
};
} // namespace ROCKSDB_NAMESPACE