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perf bench futex: Fix hung wakeup tasks after requeueing

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The futex-requeue benchmark can hang because of missing wakeups once the
benchmark is done, ie:

[Run 1]: Requeued 1024 of 1024 threads in 0.3290 ms
perf: couldn't wakeup all tasks (135/1024)

This bug, while perhaps suggesting missing wakeups in kernel futex code,
is merely a consequence of the crappy FUTEX_CMP_REQUEUE man page,
incorrectly mentioning that the number of requeued tasks is in fact
returned, not the wakeups.

This patch acknowledges this and updates the corresponding futex_wake
code around it.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Mel Gorman <mgorman@suse.de>
Link: http://lkml.kernel.org/r/1429894848.10273.44.camel@stgolabs.net
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Davidlohr Bueso 2015-04-24 10:00:48 -07:00 committed by Arnaldo Carvalho de Melo
parent d13855ef18
commit 052b0f6eaf
1 changed files with 8 additions and 7 deletions
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15
tools/perf/bench/futex-requeue.c
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@ -132,6 +132,9 @@ int bench_futex_requeue(int argc, const char **argv,
if (!fshared)
futex_flag = FUTEX_PRIVATE_FLAG;
if (nrequeue > nthreads)
nrequeue = nthreads;
printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %p), "
"%d at a time.\n\n", getpid(), nthreads,
fshared ? "shared":"private", &futex1, &futex2, nrequeue);
@ -161,20 +164,18 @@ int bench_futex_requeue(int argc, const char **argv,
/* Ok, all threads are patiently blocked, start requeueing */
gettimeofday(&start, NULL);
for (nrequeued = 0; nrequeued < nthreads; nrequeued += nrequeue) {
while (nrequeued < nthreads) {
/*
* Do not wakeup any tasks blocked on futex1, allowing
* us to really measure futex_wait functionality.
*/
futex_cmp_requeue(&futex1, 0, &futex2, 0,
nrequeue, futex_flag);
nrequeued += futex_cmp_requeue(&futex1, 0, &futex2, 0,
nrequeue, futex_flag);
}
gettimeofday(&end, NULL);
timersub(&end, &start, &runtime);
if (nrequeued > nthreads)
nrequeued = nthreads;
update_stats(&requeued_stats, nrequeued);
update_stats(&requeuetime_stats, runtime.tv_usec);
@ -184,7 +185,7 @@ int bench_futex_requeue(int argc, const char **argv,
}
/* everybody should be blocked on futex2, wake'em up */
nrequeued = futex_wake(&futex2, nthreads, futex_flag);
nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
if (nthreads != nrequeued)
warnx("couldn't wakeup all tasks (%d/%d)", nrequeued, nthreads);