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Message-ID: <aUD6yGZ2bSHsCb2e@google.com>
Date: Mon, 15 Dec 2025 22:23:04 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: James Clark <james.clark@...aro.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
Ian Rogers <irogers@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
linux-perf-users@...r.kernel.org,
Ankur Arora <ankur.a.arora@...cle.com>
Subject: Re: [PATCH] perf bench: Add -t/--threads option to perf bench mem
mmap
Hi James,
On Tue, Dec 09, 2025 at 01:01:25PM +0000, James Clark wrote:
>
>
> On 07/12/2025 8:57 am, Namhyung Kim wrote:
> > So that it can measure overhead of mmap_lock and/or per-VMA lock
> > contention.
> >
> > $ perf bench mem mmap -f demand -l 1000 -t 1
> > # Running 'mem/mmap' benchmark:
> > # function 'demand' (Demand loaded mmap())
> > # Copying 1MB bytes ...
> >
> > 2.914503 GB/sec
> >
> > $ perf bench mem mmap -f demand -l 1000 -t 2
> > # Running 'mem/mmap' benchmark:
> > # function 'demand' (Demand loaded mmap())
> > # Copying 1MB bytes ...
> >
> > 888.769991 MB/sec
> >
> > $ perf bench mem mmap -f demand -l 1000 -t 3
> > # Running 'mem/mmap' benchmark:
> > # function 'demand' (Demand loaded mmap())
> > # Copying 1MB bytes ...
> >
> > 757.658220 MB/sec
> >
> > $ perf bench mem mmap -f demand -l 1000 -t 4
> > # Running 'mem/mmap' benchmark:
> > # function 'demand' (Demand loaded mmap())
> > # Copying 1MB bytes ...
> >
> > 316.410713 MB/sec
>
> Should this now say "MB/sec per thread" for nr_threads > 1? I think it could
> be interpreted either way without a label, but I see you divided by
> nr_threads in timeval2double().
Right, thanks for the review. I think we can add it unconditionally.
Thanks,
Namhyung
>
> >
> > Cc: Ankur Arora <ankur.a.arora@...cle.com>
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > ---
> > tools/perf/Documentation/perf-bench.txt | 4 ++
> > tools/perf/bench/mem-functions.c | 74 +++++++++++++++++++++----
> > 2 files changed, 67 insertions(+), 11 deletions(-)
> >
> > diff --git a/tools/perf/Documentation/perf-bench.txt b/tools/perf/Documentation/perf-bench.txt
> > index 1160224cb718392d..c5913cf59c988421 100644
> > --- a/tools/perf/Documentation/perf-bench.txt
> > +++ b/tools/perf/Documentation/perf-bench.txt
> > @@ -274,6 +274,10 @@ Repeat mmap() invocation this number of times.
> > --cycles::
> > Use perf's cpu-cycles event instead of gettimeofday syscall.
> > +-t::
> > +--threads=<NUM>::
> > +Create multiple threads to call mmap/munmap concurrently.
> > +
> > SUITES FOR 'numa'
> > ~~~~~~~~~~~~~~~~~
> > *mem*::
> > diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
> > index 2908a3a796c932d0..e7e7d0b41fc7720f 100644
> > --- a/tools/perf/bench/mem-functions.c
> > +++ b/tools/perf/bench/mem-functions.c
> > @@ -26,6 +26,7 @@
> > #include <errno.h>
> > #include <linux/time64.h>
> > #include <linux/log2.h>
> > +#include <pthread.h>
> > #define K 1024
> > @@ -41,6 +42,7 @@ static unsigned int nr_loops = 1;
> > static bool use_cycles;
> > static int cycles_fd;
> > static unsigned int seed;
> > +static unsigned int nr_threads = 1;
> > static const struct option bench_common_options[] = {
> > OPT_STRING('s', "size", &size_str, "1MB",
> > @@ -174,7 +176,7 @@ static void clock_accum(union bench_clock *a, union bench_clock *b)
> > static double timeval2double(struct timeval *ts)
> > {
> > - return (double)ts->tv_sec + (double)ts->tv_usec / (double)USEC_PER_SEC;
> > + return (double)ts->tv_sec + (double)ts->tv_usec / (double)USEC_PER_SEC / nr_threads;
> > }
> > #define print_bps(x) do { \
> > @@ -494,16 +496,27 @@ static void mmap_page_touch(void *dst, size_t size, unsigned int page_shift, boo
> > }
> > }
> > -static int do_mmap(const struct function *r, struct bench_params *p,
> > - void *src __maybe_unused, void *dst __maybe_unused,
> > - union bench_clock *accum)
> > +struct mmap_data {
> > + pthread_t id;
> > + const struct function *func;
> > + struct bench_params *params;
> > + union bench_clock result;
> > + unsigned int seed;
> > + int error;
> > +};
> > +
> > +static void *do_mmap_thread(void *arg)
> > {
> > + struct mmap_data *data = arg;
> > + const struct function *r = data->func;
> > + struct bench_params *p = data->params;
> > union bench_clock start, end, diff;
> > mmap_op_t fn = r->fn.mmap_op;
> > bool populate = strcmp(r->name, "populate") == 0;
> > + void *dst;
> > - if (p->seed)
> > - srand(p->seed);
> > + if (data->seed)
> > + srand(data->seed);
> > for (unsigned int i = 0; i < p->nr_loops; i++) {
> > clock_get(&start);
> > @@ -514,16 +527,53 @@ static int do_mmap(const struct function *r, struct bench_params *p,
> > fn(dst, p->size, p->page_shift, p->seed);
> > clock_get(&end);
> > diff = clock_diff(&start, &end);
> > - clock_accum(accum, &diff);
> > + clock_accum(&data->result, &diff);
> > bench_munmap(dst, p->size);
> > }
> > - return 0;
> > + return data;
> > out:
> > - printf("# Memory allocation failed - maybe size (%s) %s?\n", size_str,
> > - p->page_shift != PAGE_SHIFT_4KB ? "has insufficient hugepages" : "is too large");
> > - return -1;
> > + data->error = -ENOMEM;
> > + return NULL;
> > +}
> > +
> > +static int do_mmap(const struct function *r, struct bench_params *p,
> > + void *src __maybe_unused, void *dst __maybe_unused,
> > + union bench_clock *accum)
> > +{
> > + struct mmap_data *data;
> > + int error = 0;
> > +
> > + data = calloc(nr_threads, sizeof(*data));
> > + if (!data) {
> > + printf("# Failed to allocate thread resources\n");
> > + return -1;
> > + }
> > +
> > + for (unsigned int i = 0; i < nr_threads; i++) {
> > + data[i].func = r;
> > + data[i].params = p;
> > + if (p->seed)
> > + data[i].seed = p->seed + i;
> > +
> > + if (pthread_create(&data[i].id, NULL, do_mmap_thread, &data[i]) < 0)
> > + data[i].error = -errno;
> > + }
> > +
> > + for (unsigned int i = 0; i < nr_threads; i++) {
> > + pthread_join(data[i].id, NULL);
> > +
> > + clock_accum(accum, &data[i].result);
> > + error |= data[i].error;
> > + }
> > + free(data);
> > +
> > + if (error) {
> > + printf("# Memory allocation failed - maybe size (%s) %s?\n", size_str,
> > + p->page_shift != PAGE_SHIFT_4KB ? "has insufficient hugepages" : "is too large");
> > + }
> > + return error ? -1 : 0;
> > }
> > static const char * const bench_mem_mmap_usage[] = {
> > @@ -548,6 +598,8 @@ int bench_mem_mmap(int argc, const char **argv)
> > static const struct option bench_mmap_options[] = {
> > OPT_UINTEGER('r', "randomize", &seed,
> > "Seed to randomize page access offset."),
> > + OPT_UINTEGER('t', "threads", &nr_threads,
> > + "Number of threads to run concurrently (default: 1)."),
> > OPT_PARENT(bench_common_options),
> > OPT_END()
> > };
>
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