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Commit 052b0f6e authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Arnaldo Carvalho de Melo
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perf bench futex: Fix hung wakeup tasks after requeueing 



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: default avatarDavidlohr 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: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent d13855ef

tools/perf/bench/futex-requeue.c

+8 −7
Original line number Diff line number Diff line
@@ -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,

			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);