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 <dbu...@suse.de>
---
tools/perf/bench/futex-requeue.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
diff --git a/tools/perf/bench/futex-requeue.c b/tools/perf/bench/futex-requeue.c
index bedff6b..ad0d9b5 100644
--- a/tools/perf/bench/futex-requeue.c
+++ b/tools/perf/bench/futex-requeue.c
@@ -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);
--
2.1.4
--
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