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

Arnaldo Carvalho de Melo
2021-08-09T15:01:54Z

Em Sun, Aug 08, 2021 at 09:33:01PM -0700, Davidlohr Bueso escreveu:
> 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.

Thanks, applied.

- Arnaldo

> 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
>

--

- Arnaldo