Re: [PATCH] perf bench: Add -t/--threads option to perf bench mem mmap

[Namhyung Kim <namhyung@kernel.org>]

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@oracle.com>
> > Signed-off-by: Namhyung Kim <namhyung@kernel.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()
> >   	};
>