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Subject[PATCH 2/3] perf bench futex: Add --affine-wakers option to wake-parallel
Date
From: James Yang <james.yang@arm.com>

The waker threads' processor affinity is not specified, so
the result has run-to-run variability as the scheduler
decides on which CPUs they are to run. So we add a
-W/--affine-wakers flag to stripe the affinity of the
waker threads across the online CPUs instead of having
the scheduler place them.

Cc: Kim Phillips <Kim.Phillips@arm.com>
Signed-off-by: James Yang <james.yang@arm.com>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
tools/perf/bench/futex-wake-parallel.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/tools/perf/bench/futex-wake-parallel.c b/tools/perf/bench/futex-wake-parallel.c
index 979e303e4797..c04e207ea37c 100644
--- a/tools/perf/bench/futex-wake-parallel.c
+++ b/tools/perf/bench/futex-wake-parallel.c
@@ -39,6 +39,7 @@ static u_int32_t futex = 0;

static pthread_t *blocked_worker;
static bool done = false, silent = false, fshared = false;
+static bool affine_wakers = false;
static unsigned int nblocked_threads = 0, nwaking_threads = 0;
static pthread_mutex_t thread_lock;
static pthread_cond_t thread_parent, thread_worker;
@@ -51,6 +52,7 @@ static const struct option options[] = {
OPT_UINTEGER('w', "nwakers", &nwaking_threads, "Specify amount of waking threads"),
OPT_BOOLEAN( 's', "silent", &silent, "Silent mode: do not display data/details"),
OPT_BOOLEAN( 'S', "shared", &fshared, "Use shared futexes instead of private ones"),
+ OPT_BOOLEAN( 'W', "affine-wakers", &affine_wakers, "Stripe affinity of waker threads across CPUs"),
OPT_END()
};

@@ -78,7 +80,8 @@ static void *waking_workerfn(void *arg)
return NULL;
}

-static void wakeup_threads(struct thread_data *td, pthread_attr_t thread_attr)
+static void wakeup_threads(struct thread_data *td, pthread_attr_t thread_attr,
+ struct cpu_map *cpu)
{
unsigned int i;

@@ -91,6 +94,17 @@ static void wakeup_threads(struct thread_data *td, pthread_attr_t thread_attr)
* as it will affect the order to acquire the hb spinlock.
* For now let the scheduler decide.
*/
+ if (affine_wakers) {
+ cpu_set_t cpuset;
+ CPU_ZERO(&cpuset);
+ CPU_SET(cpu->map[(i + 1) % cpu->nr], &cpuset);
+
+ if (pthread_attr_setaffinity_np(&thread_attr,
+ sizeof(cpu_set_t),
+ &cpuset))
+ err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
+ }
+
if (pthread_create(&td[i].worker, &thread_attr,
waking_workerfn, (void *)&td[i]))
err(EXIT_FAILURE, "pthread_create");
@@ -276,7 +290,7 @@ int bench_futex_wake_parallel(int argc, const char **argv)
usleep(100000);

/* Ok, all threads are patiently blocked, start waking folks up */
- wakeup_threads(waking_worker, thread_attr);
+ wakeup_threads(waking_worker, thread_attr, cpu);

for (i = 0; i < nblocked_threads; i++) {
ret = pthread_join(blocked_worker[i], NULL);
--
2.13.6
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