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Message-Id: <20210806013329.94627-4-dave@stgolabs.net>
Date: Thu, 5 Aug 2021 18:33:29 -0700
From: Davidlohr Bueso <dave@...olabs.net>
To: acme@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
dave@...olabs.net, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 3/3] perf/bench-futex, requeue: Add --pi parameter
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@...e.de>
---
tools/perf/bench/futex-requeue.c | 81 +++++++++++++++++++++++++-------
tools/perf/bench/futex.h | 40 ++++++++++++++--
2 files changed, 100 insertions(+), 21 deletions(-)
diff --git a/tools/perf/bench/futex-requeue.c b/tools/perf/bench/futex-requeue.c
index 51f2c0d5e6f8..fcbf04235d94 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 */
@@ -41,7 +42,8 @@ static int futex_flag = 0;
struct parameters {
unsigned int nthreads;
- unsigned int nrequeue;
+ unsigned int nrequeue;
+ bool pi;
bool silent;
bool fshared;
bool mlockall;
@@ -60,6 +62,8 @@ static const struct option options[] = {
"Specify amount of threads"),
OPT_UINTEGER('q', "nrequeue", ¶ms.nrequeue,
"Specify amount of threads to requeue at once"),
+ OPT_BOOLEAN( 'p', "pi", ¶ms.pi,
+ "Use PI-aware variants of FUTEX_CMP_REQUEUE"),
OPT_BOOLEAN( 's', "silent", ¶ms.silent,
"Silent mode: do not display data/details"),
OPT_BOOLEAN( 'S', "shared", ¶ms.fshared,
@@ -96,7 +100,18 @@ static void *workerfn(void *arg __maybe_unused)
pthread_cond_wait(&thread_worker, &thread_lock);
pthread_mutex_unlock(&thread_lock);
- futex_wait(&futex1, 0, NULL, futex_flag);
+ if (!params.pi)
+ futex_wait(&futex1, 0, NULL, futex_flag);
+ else {
+ int ret = futex_wait_requeue_pi(&futex1, 0, &futex2,
+ NULL, futex_flag);
+ if (ret)
+ warnx("waiter was not requeued");
+ else
+ futex_unlock_pi(&futex2, futex_flag);
+ }
+
+
return NULL;
}
@@ -167,9 +182,10 @@ int bench_futex_requeue(int argc, const char **argv)
if (params.nrequeue > params.nthreads)
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);
@@ -179,7 +195,7 @@ 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 */
@@ -197,13 +213,30 @@ 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);
@@ -213,16 +246,28 @@ 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) {
+ nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
+ if (params.nthreads != nrequeued)
+ err(EXIT_FAILURE, "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 31b53cc7d5bc..f64a3c231184 100644
--- a/tools/perf/bench/futex.h
+++ b/tools/perf/bench/futex.h
@@ -77,13 +77,47 @@ 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,
- int nr_requeue, int opflags)
+futex_cmp_requeue(u_int32_t *uaddr, u_int32_t val, u_int32_t *uaddr2,
+ int nr_wake, int nr_requeue, int opflags)
{
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
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