Date:   Mon, 9 Aug 2021 12:01:47 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 7/7] perf/bench-futex, requeue: Add --pi parameter

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@...e.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

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