From: Tommi Rantala <tommi.t.rantala@nokia.com>

Date: Thu, 5 Mar 2020 10:37:13 +0200

Subject: perf bench futex-wake: Restore thread count default to online CPU

 count

Git-commit: f649bd9dd5d5004543bbc3c50b829577b49f5d75

Patch-mainline: v5.6-rc6

References: git-fixes

​

Since commit 3b2323c2c1c4 ("perf bench futex: Use cpumaps") the default

number of threads the benchmark uses got changed from number of online

CPUs to zero:

​

  $ perf bench futex wake

  # Running 'futex/wake' benchmark:

  Run summary [PID 15930]: blocking on 0 threads (at [private] futex 0x558b8ee4bfac), waking up 1 at a time.

  [Run 1]: Wokeup 0 of 0 threads in 0.0000 ms

  [...]

  [Run 10]: Wokeup 0 of 0 threads in 0.0000 ms

  Wokeup 0 of 0 threads in 0.0004 ms (+-40.82%)

​

Restore the old behavior by grabbing the number of online CPUs via

cpu->nr:

​

  $ perf bench futex wake

  # Running 'futex/wake' benchmark:

  Run summary [PID 18356]: blocking on 8 threads (at [private] futex 0xb3e62c), waking up 1 at a time.

  [Run 1]: Wokeup 8 of 8 threads in 0.0260 ms

  [...]

  [Run 10]: Wokeup 8 of 8 threads in 0.0270 ms

  Wokeup 8 of 8 threads in 0.0419 ms (+-24.35%)

​

Fixes: 3b2323c2c1c4 ("perf bench futex: Use cpumaps")

Signed-off-by: Tommi Rantala <tommi.t.rantala@nokia.com>

Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>

Cc: Darren Hart <dvhart@infradead.org>

Cc: Davidlohr Bueso <dave@stgolabs.net>

Cc: Jiri Olsa <jolsa@redhat.com>

Cc: Mark Rutland <mark.rutland@arm.com>

Cc: Namhyung Kim <namhyung@kernel.org>

Cc: Peter Zijlstra <peterz@infradead.org>

Cc: Thomas Gleixner <tglx@linutronix.de>

Link: http://lore.kernel.org/lkml/20200305083714.9381-3-tommi.t.rantala@nokia.com

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Signed-off-by: Tony Jones <tonyj@suse.de>

---

 tools/perf/bench/futex-wake.c | 4 ++--

 1 file changed, 2 insertions(+), 2 deletions(-)

​

diff --git a/tools/perf/bench/futex-wake.c b/tools/perf/bench/futex-wake.c

index df810096abfe..58906e9499bb 100644

--- a/tools/perf/bench/futex-wake.c

+++ b/tools/perf/bench/futex-wake.c

@@ -43,7 +43,7 @@ static bool done = false, silent = false, fshared = false;

 static pthread_mutex_t thread_lock;

 static pthread_cond_t thread_parent, thread_worker;

 static struct stats waketime_stats, wakeup_stats;

-static unsigned int ncpus, threads_starting, nthreads = 0;

+static unsigned int threads_starting, nthreads = 0;

 static int futex_flag = 0;

 static const struct option options[] = {

@@ -141,7 +141,7 @@ int bench_futex_wake(int argc, const char **argv)

    sigaction(SIGINT, &act, NULL);

    if (!nthreads)

-       nthreads = ncpus;

+       nthreads = cpu->nr;

    worker = calloc(nthreads, sizeof(*worker));

    if (!worker)

​

​