From: Namhyung Kim <namhyung@kernel.org>
To: Michal Pluta <michalpl2003@gmail.com>
Cc: acme@kernel.org, "Thomas Gleixner" <tglx@kernel.org>,
"Ingo Molnar" <mingo@redhat.com>,
"Peter Zijlstra" <peterz@infradead.org>,
"Darren Hart" <dvhart@infradead.org>,
"Davidlohr Bueso" <dave@stgolabs.net>,
"André Almeida" <andrealmeid@igalia.com>,
"Mark Rutland" <mark.rutland@arm.com>,
"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
"Jiri Olsa" <jolsa@kernel.org>, "Ian Rogers" <irogers@google.com>,
"Adrian Hunter" <adrian.hunter@intel.com>,
"James Clark" <james.clark@linaro.org>,
"Sebastian Andrzej Siewior" <bigeasy@linutronix.de>,
linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org
Subject: Re: [PATCH 3/8] perf bench futex: Use the whole timeval for elapsed times
Date: Mon, 5 Oct 2026 16:54:26 -0700 [thread overview]
Message-ID: <asQ4sju-WXehW8oP@google.com> (raw)
In-Reply-To: <20260926190407.1106421-4-michalpl2003@gmail.com>
On Sat, Sep 26, 2026 at 08:04:02PM +0100, Michal Pluta wrote:
> Several futex benchmarks read only one field of the struct timeval that
> timersub() produces, so part of the elapsed time is lost.
>
> 'futex wake', 'futex wake-parallel' and 'futex requeue' print tv_usec,
> so a run that takes 1.5 s is shown as 500 ms. 'futex hash' and 'futex
> lock-pi' divide their operation count by tv_sec, which overstates the
> throughput when a run is stopped early, and gives 0 if that happens
> within the first second. Their "total secs" is truncated in the same
> way.
>
> Use the whole timeval and print "total secs" with two decimals. With
> --runtime=0 the rate is now computed over the time that actually
> elapsed, instead of showing 0.
Can you please add an example output of one of the benchmarks in the
commit message?
Thanks,
Namhyung
>
> Fixes: 27db78307481 ("perf bench: Add futex-wake microbenchmark")
> Fixes: 0fb298cf95c0 ("perf bench: Add futex-requeue microbenchmark")
> Fixes: a043971141f1 ("perf bench: Add futex-hash microbenchmark")
> Fixes: d2f3f5d2e9ca ("perf bench futex: Add lock_pi stresser")
> Fixes: d65817b4e707 ("perf bench futex: Support parallel waker threads")
> Assisted-by: LLM
> Signed-off-by: Michal Pluta <michalpl2003@gmail.com>
> ---
> tools/perf/bench/futex-hash.c | 12 ++++++++----
> tools/perf/bench/futex-lock-pi.c | 12 ++++++++----
> tools/perf/bench/futex-requeue.c | 8 +++++---
> tools/perf/bench/futex-wake-parallel.c | 8 ++++++--
> tools/perf/bench/futex-wake.c | 6 ++++--
> 5 files changed, 31 insertions(+), 15 deletions(-)
>
> diff --git a/tools/perf/bench/futex-hash.c b/tools/perf/bench/futex-hash.c
> index 7e29f04da744..32b88df8ee6d 100644
> --- a/tools/perf/bench/futex-hash.c
> +++ b/tools/perf/bench/futex-hash.c
> @@ -18,6 +18,7 @@
> #include <stdlib.h>
> #include <linux/compiler.h>
> #include <linux/kernel.h>
> +#include <linux/time64.h>
> #include <linux/zalloc.h>
> #include <sys/time.h>
> #include <sys/mman.h>
> @@ -118,18 +119,19 @@ static void print_summary(void)
> unsigned long avg = avg_stats(&throughput_stats);
> double stddev = stddev_stats(&throughput_stats);
>
> - printf("%sAveraged %ld operations/sec (+- %.2f%%), total secs = %d\n",
> + printf("%sAveraged %ld operations/sec (+- %.2f%%), total secs = %.2f\n",
> !params.silent ? "\n" : "", avg, rel_stddev_stats(stddev, avg),
> - (int)bench__runtime.tv_sec);
> + bench__runtime.tv_sec + bench__runtime.tv_usec / (double)USEC_PER_SEC);
> futex_print_nbuckets(¶ms);
> }
>
> int bench_futex_hash(int argc, const char **argv)
> {
> int ret = 0;
> cpu_set_t *cpuset;
> struct sigaction act;
> unsigned int i;
> + u64 runtime_us;
> pthread_attr_t thread_attr;
> struct worker *worker = NULL;
> struct perf_cpu_map *cpu;
> @@ -229,9 +231,11 @@ int bench_futex_hash(int argc, const char **argv)
> cond_destroy(&thread_worker);
> mutex_destroy(&thread_lock);
>
> + runtime_us = (u64)bench__runtime.tv_sec * USEC_PER_SEC + bench__runtime.tv_usec;
> +
> for (i = 0; i < params.nthreads; i++) {
> - unsigned long t = bench__runtime.tv_sec > 0 ?
> - worker[i].ops / bench__runtime.tv_sec : 0;
> + unsigned long t = runtime_us ?
> + (u64)worker[i].ops * USEC_PER_SEC / runtime_us : 0;
> update_stats(&throughput_stats, t);
> if (!params.silent) {
> if (params.nfutexes == 1)
> diff --git a/tools/perf/bench/futex-lock-pi.c b/tools/perf/bench/futex-lock-pi.c
> index 40640b674427..7190f5102e09 100644
> --- a/tools/perf/bench/futex-lock-pi.c
> +++ b/tools/perf/bench/futex-lock-pi.c
> @@ -13,6 +13,7 @@
> #include <subcmd/parse-options.h>
> #include <linux/compiler.h>
> #include <linux/kernel.h>
> +#include <linux/time64.h>
> #include <linux/zalloc.h>
> #include <errno.h>
> #include <perf/cpumap.h>
> @@ -66,9 +67,9 @@ static void print_summary(void)
> unsigned long avg = avg_stats(&throughput_stats);
> double stddev = stddev_stats(&throughput_stats);
>
> - printf("%sAveraged %ld operations/sec (+- %.2f%%), total secs = %d\n",
> + printf("%sAveraged %ld operations/sec (+- %.2f%%), total secs = %.2f\n",
> !params.silent ? "\n" : "", avg, rel_stddev_stats(stddev, avg),
> - (int)bench__runtime.tv_sec);
> + bench__runtime.tv_sec + bench__runtime.tv_usec / (double)USEC_PER_SEC);
> futex_print_nbuckets(¶ms);
> }
>
> @@ -168,6 +169,7 @@ int bench_futex_lock_pi(int argc, const char **argv)
> {
> int ret = 0;
> unsigned int i;
> + u64 runtime_us;
> struct sigaction act;
> struct perf_cpu_map *cpu;
>
> @@ -233,9 +235,11 @@ int bench_futex_lock_pi(int argc, const char **argv)
> cond_destroy(&thread_worker);
> mutex_destroy(&thread_lock);
>
> + runtime_us = (u64)bench__runtime.tv_sec * USEC_PER_SEC + bench__runtime.tv_usec;
> +
> for (i = 0; i < params.nthreads; i++) {
> - unsigned long t = bench__runtime.tv_sec > 0 ?
> - worker[i].ops / bench__runtime.tv_sec : 0;
> + unsigned long t = runtime_us ?
> + (u64)worker[i].ops * USEC_PER_SEC / runtime_us : 0;
>
> update_stats(&throughput_stats, t);
> if (!params.silent)
> diff --git a/tools/perf/bench/futex-requeue.c b/tools/perf/bench/futex-requeue.c
> index 0748b0fd689e..5d4708f40c60 100644
> --- a/tools/perf/bench/futex-requeue.c
> +++ b/tools/perf/bench/futex-requeue.c
> @@ -223,6 +223,7 @@ int bench_futex_requeue(int argc, const char **argv)
> for (j = 0; j < bench_repeat && !done; j++) {
> unsigned int nrequeued = 0, wakeups = 0;
> struct timeval start, end, runtime;
> + u64 runtime_us;
>
> /* create, launch & block all threads */
> block_threads(worker, cpu);
> @@ -267,23 +268,24 @@ int bench_futex_requeue(int argc, const char **argv)
>
> gettimeofday(&end, NULL);
> timersub(&end, &start, &runtime);
> + runtime_us = (u64)runtime.tv_sec * USEC_PER_SEC + runtime.tv_usec;
>
> update_stats(&requeued_stats, nrequeued);
> - update_stats(&requeuetime_stats, runtime.tv_usec);
> + update_stats(&requeuetime_stats, runtime_us);
>
> if (!params.silent) {
> 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);
> + runtime_us / (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);
> + runtime_us / (double)USEC_PER_MSEC);
> }
>
> }
> diff --git a/tools/perf/bench/futex-wake-parallel.c b/tools/perf/bench/futex-wake-parallel.c
> index a089d8ee4b02..fa70b7d4b473 100644
> --- a/tools/perf/bench/futex-wake-parallel.c
> +++ b/tools/perf/bench/futex-wake-parallel.c
> @@ -192,7 +192,9 @@ static void print_run(struct thread_data *waking_worker, unsigned int run_num)
> init_stats(&__waketime_stats);
>
> for (i = 0; i < params.nwakes; i++) {
> - update_stats(&__waketime_stats, waking_worker[i].runtime.tv_usec);
> + update_stats(&__waketime_stats,
> + (u64)waking_worker[i].runtime.tv_sec * USEC_PER_SEC +
> + waking_worker[i].runtime.tv_usec);
> update_stats(&__wakeup_stats, waking_worker[i].nwoken);
> }
>
> @@ -229,7 +231,9 @@ static void do_run_stats(struct thread_data *waking_worker)
> unsigned int i;
>
> for (i = 0; i < params.nwakes; i++) {
> - update_stats(&waketime_stats, waking_worker[i].runtime.tv_usec);
> + update_stats(&waketime_stats,
> + (u64)waking_worker[i].runtime.tv_sec * USEC_PER_SEC +
> + waking_worker[i].runtime.tv_usec);
> update_stats(&wakeup_stats, waking_worker[i].nwoken);
> }
>
> diff --git a/tools/perf/bench/futex-wake.c b/tools/perf/bench/futex-wake.c
> index 58427bb55c03..12a75be077a0 100644
> --- a/tools/perf/bench/futex-wake.c
> +++ b/tools/perf/bench/futex-wake.c
> @@ -191,6 +191,7 @@ int bench_futex_wake(int argc, const char **argv)
> for (j = 0; j < bench_repeat && !done; j++) {
> unsigned int nwoken = 0;
> struct timeval start, end, runtime;
> + u64 runtime_us;
>
> /* create, launch & block all threads */
> block_threads(worker, cpu);
> @@ -211,14 +212,15 @@ int bench_futex_wake(int argc, const char **argv)
> params.nwakes, futex_flag);
> gettimeofday(&end, NULL);
> timersub(&end, &start, &runtime);
> + runtime_us = (u64)runtime.tv_sec * USEC_PER_SEC + runtime.tv_usec;
>
> update_stats(&wakeup_stats, nwoken);
> - update_stats(&waketime_stats, runtime.tv_usec);
> + update_stats(&waketime_stats, runtime_us);
>
> if (!params.silent) {
> printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
> j + 1, nwoken, params.nthreads,
> - runtime.tv_usec / (double)USEC_PER_MSEC);
> + runtime_us / (double)USEC_PER_MSEC);
> }
>
> for (i = 0; i < params.nthreads; i++) {
> --
> 2.43.0
>
next prev parent reply other threads:[~2026-10-05 23:54 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-26 19:03 [PATCH 0/8] perf bench futex: Fix several bugs and bad inputs Michal Pluta
2026-09-26 19:04 ` [PATCH 1/8] perf bench futex: Retry futex_wait() when interrupted by a signal Michal Pluta
2026-09-26 19:04 ` [PATCH 2/8] perf bench futex: Set the number of hash buckets in futex wake Michal Pluta
2026-09-26 19:04 ` [PATCH 3/8] perf bench futex: Use the whole timeval for elapsed times Michal Pluta
2026-10-05 23:54 ` Namhyung Kim [this message]
2026-09-26 19:04 ` [PATCH 4/8] perf bench futex: Reject invalid -q, -f and -b values Michal Pluta
2026-09-26 19:04 ` [PATCH 5/8] perf bench futex: Stop when futex_wake() fails in futex wake Michal Pluta
2026-09-26 19:04 ` [PATCH 6/8] perf bench futex: Use a 64-bit operation counter in hash and lock-pi Michal Pluta
2026-09-26 19:04 ` [PATCH 7/8] perf bench futex: Clean up two nits in futex hash Michal Pluta
2026-09-26 19:04 ` [PATCH 8/8] perf bench futex: Fix wording in futex bench messages Michal Pluta
2026-10-05 23:57 ` Namhyung Kim
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