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Do not sleep, but yield

Browse source 
During the search, do not block on condition variable, but instead use std::this_thread::yield().

Clear gain with 16 threads. Again results vary highly depending on hardware, but on average it's a clear gain.

ELO: 12.17 +-4.3 (95%) LOS: 100.0%
Total: 7998 W: 1407 L: 1127 D: 5464

There is no functional change in single thread mode

Resolves #294
This commit is contained in:
Joona Kiiski 2015-03-15 19:45:30 +00:00
parent a4b98a052e
commit f04f50b368
2 changed files with 21 additions and 28 deletions
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43
src/search.cpp
View file

@ -1595,8 +1595,25 @@ void Thread::idle_loop() {
assert(!this_sp || (this_sp->master == this && searching));
while (!exit)
while ( !exit
&& !(this_sp && this_sp->slavesMask.none()))
{
// If there is nothing to do, sleep.
while( !exit
&& !(this_sp && this_sp->slavesMask.none())
&& !searching)
{
if ( !this_sp
&& !Threads.main()->thinking)
{
std::unique_lock<Mutex> lk(mutex);
while (!exit && !Threads.main()->thinking)
sleepCondition.wait(lk);
}
else
std::this_thread::yield();
}
// If this thread has been assigned work, launch a search
while (searching)
{
@ -1639,15 +1656,6 @@ void Thread::idle_loop() {
sp->allSlavesSearching = false;
sp->nodes += pos.nodes_searched();
// Wake up the master thread so to allow it to return from the idle
// loop in case we are the last slave of the split point.
if (this != sp->master && sp->slavesMask.none())
{
assert(!sp->master->searching);
sp->master->notify_one();
}
// After releasing the lock we can't access any SplitPoint related data
// in a safe way because it could have been released under our feet by
// the sp master.
@ -1711,21 +1719,6 @@ void Thread::idle_loop() {
sp->mutex.unlock();
}
}
// Avoid races with notify_one() fired from last slave of the split point
std::unique_lock<Mutex> lk(mutex);
// If we are master and all slaves have finished then exit idle_loop
if (this_sp && this_sp->slavesMask.none())
{
assert(!searching);
break;
}
// If we are not searching, wait for a condition to be signaled instead of
// wasting CPU time polling for work.
if (!searching && !exit)
sleepCondition.wait(lk);
}
}

6
src/thread.cpp
View file

@ -184,8 +184,6 @@ void Thread::split(Position& pos, Stack* ss, Value alpha, Value beta, Value* bes
}
slave->allocMutex.unlock();
slave->notify_one(); // Could be sleeping
}
// Everything is set up. The master thread enters the idle loop, from which
@ -375,5 +373,7 @@ void ThreadPool::start_thinking(const Position& pos, const LimitsType& limits,
RootMoves.push_back(RootMove(m));
main()->thinking = true;
main()->notify_one(); // Starts main thread
for (Thread* th : *this)
th->notify_one();
}