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| author |   Davidlohr Bueso <dave@stgolabs.net> | 2016-10-24 13:56:52 -0700 |
|---|---|---|
| committer |   Arnaldo Carvalho de Melo <acme@redhat.com> | 2016-10-25 09:50:47 -0300 |
| commit | e2e1680fda1573ebfdd6bba5d58f978044746993 (patch) | |
| tree | bb48b64d2f133ca7ea7b3a84305b3bdb4cb03b5a /tools/perf/bench/futex-lock-pi.c | |
| parent | Merge tag 'perf-core-for-mingo-20161024' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into perf/core (diff) | |
| download | linux-dev-e2e1680fda1573ebfdd6bba5d58f978044746993.tar.xz linux-dev-e2e1680fda1573ebfdd6bba5d58f978044746993.zip | |
perf bench futex: Avoid worker cacheline bouncing
Sebastian noted that overhead for worker thread ops (throughput)
accounting was producing 'perf' to appear in the profiles, consuming a
non-trivial (i.e. 13%) amount of CPU.
This is due to cacheline bouncing due to the increment of w->ops.
We can easily fix this by just working on a local copy and updating the
actual worker once done running, and ready to show the program summary.
There is no danger of the worker being concurrent, so we can trust that
no stale value is being seen by another thread.
This also gets rid of the unnecessary cache alignment hack; its not
worth it.
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: http://lkml.kernel.org/r/1477342613-9938-2-git-send-email-dave@stgolabs.net
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools/perf/bench/futex-lock-pi.c')
| -rw-r--r-- | tools/perf/bench/futex-lock-pi.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/tools/perf/bench/futex-lock-pi.c b/tools/perf/bench/futex-lock-pi.c index 936d89d30483..7032e4643c65 100644 --- a/tools/perf/bench/futex-lock-pi.c +++ b/tools/perf/bench/futex-lock-pi.c @@ -75,6 +75,7 @@ static void toggle_done(int sig __maybe_unused, static void *workerfn(void *arg) { struct worker *w = (struct worker *) arg; + unsigned long ops = w->ops; pthread_mutex_lock(&thread_lock); threads_starting--; @@ -103,9 +104,10 @@ static void *workerfn(void *arg) if (ret && !silent) warn("thread %d: Could not unlock pi-lock for %p (%d)", w->tid, w->futex, ret); - w->ops++; /* account for thread's share of work */ + ops++; /* account for thread's share of work */ } while (!done); + w->ops = ops; return NULL; } |