[PATCH 7/7] perf/bench-futex, requeue: Add --pi parameter

Davidlohr Bueso
2021-08-09T04:33:40Z

This extends the program to measure WAIT_REQUEUE_PI+CMP_REQUEUE_PI
pairs, which are the underlying machinery behind priority-inheritance
aware condition variables. The defaults are the same as with the regular
non-pi version, requeueing one task at a time, with the exception that
PI will always wakeup the first waiter.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
tools/perf/bench/futex-requeue.c | 100 +++++++++++++++++++++++--------
tools/perf/bench/futex.h | 37 +++++++++++-
2 files changed, 111 insertions(+), 26 deletions(-)

diff --git a/tools/perf/bench/futex-requeue.c b/tools/perf/bench/futex-requeue.c
index e4892ba6864f..03a05814d45e 100644
--- a/tools/perf/bench/futex-requeue.c
+++ b/tools/perf/bench/futex-requeue.c
@@ -6,7 +6,8 @@
* on futex2, N at a time.
*
* This program is particularly useful to measure the latency of nthread
- * requeues without waking up any tasks -- thus mimicking a regular futex_wait.
+ * requeues without waking up any tasks (in the non-pi case) -- thus
+ * mimicking a regular futex_wait.
*/

/* For the CLR_() macros */
@@ -53,6 +54,8 @@ static const struct option options[] = {
OPT_BOOLEAN( 'S', "shared", &params.fshared, "Use shared futexes instead of private ones"),
OPT_BOOLEAN( 'm', "mlockall", &params.mlockall, "Lock all current and future memory"),
OPT_BOOLEAN( 'B', "broadcast", &params.broadcast, "Requeue all threads at once"),
+ OPT_BOOLEAN( 'p', "pi", &params.pi, "Use PI-aware variants of FUTEX_CMP_REQUEUE"),
+
OPT_END()
};

@@ -86,14 +89,30 @@ static void *workerfn(void *arg __maybe_unused)
pthread_mutex_unlock(&thread_lock);

while (1) {
- ret = futex_wait(&futex1, 0, NULL, futex_flag);
- if (!ret)
- break;
-
- if (ret && errno != EAGAIN) {
- if (!params.silent)
- warn("futex_wait");
- break;
+ if (!params.pi) {
+ ret = futex_wait(&futex1, 0, NULL, futex_flag);
+ if (!ret)
+ break;
+
+ if (ret && errno != EAGAIN) {
+ if (!params.silent)
+ warnx("futex_wait");
+ break;
+ }
+ } else {
+ ret = futex_wait_requeue_pi(&futex1, 0, &futex2,
+ NULL, futex_flag);
+ if (!ret) {
+ /* got the lock at futex2 */
+ futex_unlock_pi(&futex2, futex_flag);
+ break;
+ }
+
+ if (ret && errno != EAGAIN) {
+ if (!params.silent)
+ warnx("futex_wait_requeue_pi");
+ break;
+ }
}
}

@@ -170,9 +189,10 @@ int bench_futex_requeue(int argc, const char **argv)
if (params.broadcast)
params.nrequeue = params.nthreads;

- printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %p), "
+ printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %s%p), "
"%d at a time.\n\n", getpid(), params.nthreads,
- params.fshared ? "shared":"private", &futex1, &futex2, params.nrequeue);
+ params.fshared ? "shared":"private", &futex1,
+ params.pi ? "PI ": "", &futex2, params.nrequeue);

init_stats(&requeued_stats);
init_stats(&requeuetime_stats);
@@ -182,7 +202,7 @@ int bench_futex_requeue(int argc, const char **argv)
pthread_cond_init(&thread_worker, NULL);

for (j = 0; j < bench_repeat && !done; j++) {
- unsigned int nrequeued = 0;
+ unsigned int nrequeued = 0, wakeups = 0;
struct timeval start, end, runtime;

/* create, launch & block all threads */
@@ -200,13 +220,30 @@ int bench_futex_requeue(int argc, const char **argv)
/* Ok, all threads are patiently blocked, start requeueing */
gettimeofday(&start, NULL);
while (nrequeued < params.nthreads) {
+ int r;
+
/*
- * Do not wakeup any tasks blocked on futex1, allowing
- * us to really measure futex_wait functionality.
+ * For the regular non-pi case, do not wakeup any tasks
+ * blocked on futex1, allowing us to really measure
+ * futex_wait functionality. For the PI case the first
+ * waiter is always awoken.
*/
- nrequeued += futex_cmp_requeue(&futex1, 0, &futex2, 0,
- params.nrequeue,
- futex_flag);
+ if (!params.pi) {
+ r = futex_cmp_requeue(&futex1, 0, &futex2, 0,
+ params.nrequeue,
+ futex_flag);
+ } else {
+ r = futex_cmp_requeue_pi(&futex1, 0, &futex2,
+ params.nrequeue,
+ futex_flag);
+ wakeups++; /* assume no error */
+ }
+
+ if (r < 0)
+ err(EXIT_FAILURE, "couldn't requeue from %p to %p",
+ &futex1, &futex2);
+
+ nrequeued += r;
}

gettimeofday(&end, NULL);
@@ -216,16 +253,29 @@ int bench_futex_requeue(int argc, const char **argv)
update_stats(&requeuetime_stats, runtime.tv_usec);

if (!params.silent) {
- printf("[Run %d]: Requeued %d of %d threads in %.4f ms\n",
- j + 1, nrequeued, params.nthreads,
- runtime.tv_usec / (double)USEC_PER_MSEC);
+ if (!params.pi)
+ printf("[Run %d]: Requeued %d of %d threads in "
+ "%.4f ms\n", j + 1, nrequeued,
+ params.nthreads,
+ runtime.tv_usec / (double)USEC_PER_MSEC);
+ else {
+ nrequeued -= wakeups;
+ printf("[Run %d]: Awoke and Requeued (%d+%d) of "
+ "%d threads in %.4f ms\n",
+ j + 1, wakeups, nrequeued,
+ params.nthreads,
+ runtime.tv_usec / (double)USEC_PER_MSEC);
+ }
+
}

- /* everybody should be blocked on futex2, wake'em up */
- nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
- if (params.nthreads != nrequeued)
- warnx("couldn't wakeup all tasks (%d/%d)",
- nrequeued, params.nthreads);
+ if (!params.pi) {
+ /* everybody should be blocked on futex2, wake'em up */
+ nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
+ if (params.nthreads != nrequeued)
+ warnx("couldn't wakeup all tasks (%d/%d)",
+ nrequeued, params.nthreads);
+ }

for (i = 0; i < params.nthreads; i++) {
ret = pthread_join(worker[i], NULL);
diff --git a/tools/perf/bench/futex.h b/tools/perf/bench/futex.h
index 36f158650edf..f0ad6d988349 100644
--- a/tools/perf/bench/futex.h
+++ b/tools/perf/bench/futex.h
@@ -21,6 +21,7 @@ struct bench_futex_parameters {
bool fshared;
bool mlockall;
bool multi; /* lock-pi */
+ bool pi; /* requeue-pi */
bool broadcast; /* requeue */
unsigned int runtime; /* seconds*/
unsigned int nthreads;
@@ -93,7 +94,7 @@ futex_unlock_pi(u_int32_t *uaddr, int opflags)
/**
* futex_cmp_requeue() - requeue tasks from uaddr to uaddr2
* @nr_wake: wake up to this many tasks
-* @nr_requeue: requeue up to this many tasks
+* @nr_requeue: requeue up to this many tasks
*/
static inline int
futex_cmp_requeue(u_int32_t *uaddr, u_int32_t val, u_int32_t *uaddr2, int nr_wake,
@@ -102,4 +103,38 @@ futex_cmp_requeue(u_int32_t *uaddr, u_int32_t val, u_int32_t *uaddr2, int nr_wak
return futex(uaddr, FUTEX_CMP_REQUEUE, nr_wake, nr_requeue, uaddr2,
val, opflags);
}
+
+/**
+ * futex_wait_requeue_pi() - block on uaddr and prepare to requeue to uaddr2
+ * @uaddr: non-PI futex source
+ * @uaddr2: PI futex target
+ *
+ * This is the first half of the requeue_pi mechanism. It shall always be
+ * paired with futex_cmp_requeue_pi().
+ */
+static inline int
+futex_wait_requeue_pi(u_int32_t *uaddr, u_int32_t val, u_int32_t *uaddr2,
+ struct timespec *timeout, int opflags)
+{
+ return futex(uaddr, FUTEX_WAIT_REQUEUE_PI, val, timeout, uaddr2, 0,
+ opflags);
+}
+
+/**
+ * futex_cmp_requeue_pi() - requeue tasks from uaddr to uaddr2
+ * @uaddr: non-PI futex source
+ * @uaddr2: PI futex target
+ * @nr_requeue: requeue up to this many tasks
+ *
+ * This is the second half of the requeue_pi mechanism. It shall always be
+ * paired with futex_wait_requeue_pi(). The first waker is always awoken.
+ */
+static inline int
+futex_cmp_requeue_pi(u_int32_t *uaddr, u_int32_t val, u_int32_t *uaddr2,
+ int nr_requeue, int opflags)
+{
+ return futex(uaddr, FUTEX_CMP_REQUEUE_PI, 1, nr_requeue, uaddr2,
+ val, opflags);
+}
+
#endif /* _FUTEX_H */
--
2.26.2