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Alleviate lock contention in the load balancing mechanism #613

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Merged
jodavies merged 1 commit into from
Feb 25, 2025
Merged

Alleviate lock contention in the load balancing mechanism #613

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19 changes: 16 additions & 3 deletions sources/threads.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3309,8 +3309,20 @@ restart:;
}
goto intercepted;
}
/* This has always been commented. Indeed no lock is held here. */
/* UNLOCK(thr->lock); */
if ( numbusy > 0 ) return(1); /* Wait a bit.... */
if ( numbusy > 0 ) {
/* JD: this avoids large runtimes for tform tests under valgrind.
What seems to happen is we return from here, goto Finalize, and
end up in LoadReadjusted again without the threads having a
chance to update their busy status. Then we end up here again.
Sleep the thread for, say, 1us to allow threads to aquire the lock. */
struct timespec sleeptime;
sleeptime.tv_sec = 0;
sleeptime.tv_nsec = 1000L;
nanosleep(&sleeptime, NULL);
return(1); /* Wait a bit.... */
}
return(0);
intercepted:;
/*
Expand All @@ -3319,8 +3331,9 @@ intercepted:;
2: find the first untreated term.
3: put the terms in the free buckets.

Remember: we have the lock to avoid interference from the thread
that is being robbed.
Remember: we still have the lock to avoid interference from the thread
that is being robbed. We were holding it and then jumped here with
goto intercepted.
*/
numinput = thr->firstterm + thr->usenum;
nperbucket = numtogo / numfree;
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