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Allow a slave to 'late join' another splitpoint

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Instead of waiting to be allocated, actively search
for another split point to join when finishes its
search. Also modify split conditions.

This patch has been tested with 7 threads SMP and
passed both STC:

LLR: 2.97 (-2.94,2.94) [-1.50,4.50]
Total: 2885 W: 519 L: 410 D: 1956

And a reduced-LTC at  25+0.05
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 4401 W: 684 L: 566 D: 3151

Was then retested against regression in 3 thread case
at standard LTC of  60+0.05:

LLR: 2.96 (-2.94,2.94) [-4.00,0.00]
Total: 40809 W: 5446 L: 5406 D: 29957

bench: 8802105
This commit is contained in:
Joona Kiiski
2014-05-03 18:29:31 +01:00
committed by Marco Costalba
parent 8f6a494ad7
commit f6e98a924a
3 changed files with 53 additions and 6 deletions
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48
src/search.cpp
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@@ -984,8 +984,10 @@ moves_loop: // When in check and at SpNode search starts from here
// Step 19. Check for splitting the search
if ( !SpNode
&& Threads.size() >= 2
&& depth >= Threads.minimumSplitDepth
&& Threads.available_slave(thisThread)
&& ( !thisThread->activeSplitPoint
|| !thisThread->activeSplitPoint->allowLatejoin)
&& thisThread->splitPointsSize < MAX_SPLITPOINTS_PER_THREAD)
{
assert(bestValue > -VALUE_INFINITE && bestValue < beta);
@@ -1527,9 +1529,9 @@ void Thread::idle_loop() {
assert(searching);
searching = false;
activePosition = NULL;
sp->slavesMask.reset(idx);
sp->allowLatejoin = false;
sp->nodes += pos.nodes_searched();
// Wake up the master thread so to allow it to return from the idle
@@ -1547,6 +1549,10 @@ void Thread::idle_loop() {
// the sp master. Also accessing other Thread objects is unsafe because
// if we are exiting there is a chance that they are already freed.
sp->mutex.unlock();
// Try to late join to another splitpoint
if (Threads.size() <= 2 || !attempt_to_latejoin()) // FIXME: attempt_to_latejoin() is theoretically unsafe when were are exiting the program...
searching = false;
}
// If this thread is the master of a split point and all slaves have finished
@@ -1562,6 +1568,44 @@ void Thread::idle_loop() {
}
}
bool Thread::attempt_to_latejoin()
{
SplitPoint *sp;
size_t i;
bool success = false;
for (i = 0; i < Threads.size(); ++i)
{
int size = Threads[i]->splitPointsSize; // Make a local copy to prevent size from changing under our feet.
sp = size ? &Threads[i]->splitPoints[size - 1] : NULL;
if ( sp
&& sp->allowLatejoin
&& available_to(Threads[i], true))
break;
}
if (i == Threads.size())
return false; // No suitable splitpoint found!
// Recheck conditions under lock protection
Threads.mutex.lock();
sp->mutex.lock();
if ( sp->allowLatejoin
&& available_to(Threads[i], true))
{
activeSplitPoint = sp;
sp->slavesMask.set(this->idx);
success = true;
}
sp->mutex.unlock();
Threads.mutex.unlock();
return success;
}
/// check_time() is called by the timer thread when the timer triggers. It is
/// used to print debug info and, more importantly, to detect when we are out of