There can be a significant gap in memset/memcpy performance depending
on the size of the region being operated on.
With chunk-size=4kb:
$ echo madvise > /sys/kernel/mm/transparent_hugepage/enabled
$ perf bench mem memset -p 4kb -k 4kb -s 4gb -l 10 -f x86-64-stosq
# Running 'mem/memset' benchmark:
# function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
# Copying 4gb bytes ...
13.011655 GB/sec
With chunk-size=1gb:
$ echo madvise > /sys/kernel/mm/transparent_hugepage/enabled
$ perf bench mem memset -p 4kb -k 1gb -s 4gb -l 10 -f x86-64-stosq
# Running 'mem/memset' benchmark:
# function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
# Copying 4gb bytes ...
21.936355 GB/sec
So, allow the user to specify the chunk-size.
The default value is identical to the total size of the region, which
preserves current behaviour.
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
tools/perf/bench/mem-functions.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index e4d713587d45..412d18f2cb2e 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -36,6 +36,7 @@
static const char *size_str = "1MB";
static const char *function_str = "all";
static const char *page_size_str = "4KB";
+static const char *chunk_size_str = "0";
static unsigned int nr_loops = 1;
static bool use_cycles;
static int cycles_fd;
@@ -49,6 +50,10 @@ static const struct option options[] = {
"Specify page-size for mapping memory buffers. "
"Available sizes: 4KB, 2MB, 1GB (case insensitive)"),
+ OPT_STRING('k', "chunk", &chunk_size_str, "0",
+ "Specify the chunk-size for each invocation. "
+ "Available units: B, KB, MB, GB and TB (case insensitive)"),
+
OPT_STRING('f', "function", &function_str, "all",
"Specify the function to run, \"all\" runs all available functions, \"help\" lists them"),
@@ -69,6 +74,7 @@ union bench_clock {
struct bench_params {
size_t size;
size_t size_total;
+ size_t chunk_size;
unsigned int nr_loops;
unsigned int page_shift;
};
@@ -242,6 +248,14 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
}
p.size_total = (size_t)p.size * p.nr_loops;
+ p.chunk_size = (size_t)perf_atoll((char *)chunk_size_str);
+ if ((s64)p.chunk_size < 0 || (s64)p.chunk_size > (s64)p.size) {
+ fprintf(stderr, "Invalid chunk_size:%s\n", chunk_size_str);
+ return 1;
+ }
+ if (!p.chunk_size)
+ p.chunk_size = p.size;
+
page_size = (unsigned int)perf_atoll((char *)page_size_str);
if (page_size != (1 << PAGE_SHIFT_4KB) &&
page_size != (1 << PAGE_SHIFT_2MB) &&
@@ -299,7 +313,8 @@ static int do_memcpy(const struct function *r, struct bench_params *p,
clock_get(&start);
for (unsigned int i = 0; i < p->nr_loops; ++i)
- fn(dst, src, p->size);
+ for (size_t off = 0; off < p->size; off += p->chunk_size)
+ fn(dst + off, src + off, min(p->chunk_size, p->size - off));
clock_get(&end);
*rt = clock_diff(&start, &end);
@@ -401,7 +416,8 @@ static int do_memset(const struct function *r, struct bench_params *p,
clock_get(&start);
for (unsigned int i = 0; i < p->nr_loops; ++i)
- fn(dst, i, p->size);
+ for (size_t off = 0; off < p->size; off += p->chunk_size)
+ fn(dst + off, i, min(p->chunk_size, p->size - off));
clock_get(&end);
*rt = clock_diff(&start, &end);
--
2.43.5On Wed, Jul 09, 2025 at 05:59:19PM -0700, Ankur Arora wrote:
> There can be a significant gap in memset/memcpy performance depending
> on the size of the region being operated on.
>
> With chunk-size=4kb:
>
> $ echo madvise > /sys/kernel/mm/transparent_hugepage/enabled
>
> $ perf bench mem memset -p 4kb -k 4kb -s 4gb -l 10 -f x86-64-stosq
> # Running 'mem/memset' benchmark:
> # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
> # Copying 4gb bytes ...
>
> 13.011655 GB/sec
>
> With chunk-size=1gb:
>
> $ echo madvise > /sys/kernel/mm/transparent_hugepage/enabled
>
> $ perf bench mem memset -p 4kb -k 1gb -s 4gb -l 10 -f x86-64-stosq
> # Running 'mem/memset' benchmark:
> # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S)
> # Copying 4gb bytes ...
>
> 21.936355 GB/sec
>
> So, allow the user to specify the chunk-size.
>
> The default value is identical to the total size of the region, which
> preserves current behaviour.
>
> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Again, please update the documentation. With that,
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Thanks,
Namhyung
> ---
> tools/perf/bench/mem-functions.c | 20 ++++++++++++++++++--
> 1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
> index e4d713587d45..412d18f2cb2e 100644
> --- a/tools/perf/bench/mem-functions.c
> +++ b/tools/perf/bench/mem-functions.c
> @@ -36,6 +36,7 @@
> static const char *size_str = "1MB";
> static const char *function_str = "all";
> static const char *page_size_str = "4KB";
> +static const char *chunk_size_str = "0";
> static unsigned int nr_loops = 1;
> static bool use_cycles;
> static int cycles_fd;
> @@ -49,6 +50,10 @@ static const struct option options[] = {
> "Specify page-size for mapping memory buffers. "
> "Available sizes: 4KB, 2MB, 1GB (case insensitive)"),
>
> + OPT_STRING('k', "chunk", &chunk_size_str, "0",
> + "Specify the chunk-size for each invocation. "
> + "Available units: B, KB, MB, GB and TB (case insensitive)"),
> +
> OPT_STRING('f', "function", &function_str, "all",
> "Specify the function to run, \"all\" runs all available functions, \"help\" lists them"),
>
> @@ -69,6 +74,7 @@ union bench_clock {
> struct bench_params {
> size_t size;
> size_t size_total;
> + size_t chunk_size;
> unsigned int nr_loops;
> unsigned int page_shift;
> };
> @@ -242,6 +248,14 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
> }
> p.size_total = (size_t)p.size * p.nr_loops;
>
> + p.chunk_size = (size_t)perf_atoll((char *)chunk_size_str);
> + if ((s64)p.chunk_size < 0 || (s64)p.chunk_size > (s64)p.size) {
> + fprintf(stderr, "Invalid chunk_size:%s\n", chunk_size_str);
> + return 1;
> + }
> + if (!p.chunk_size)
> + p.chunk_size = p.size;
> +
> page_size = (unsigned int)perf_atoll((char *)page_size_str);
> if (page_size != (1 << PAGE_SHIFT_4KB) &&
> page_size != (1 << PAGE_SHIFT_2MB) &&
> @@ -299,7 +313,8 @@ static int do_memcpy(const struct function *r, struct bench_params *p,
>
> clock_get(&start);
> for (unsigned int i = 0; i < p->nr_loops; ++i)
> - fn(dst, src, p->size);
> + for (size_t off = 0; off < p->size; off += p->chunk_size)
> + fn(dst + off, src + off, min(p->chunk_size, p->size - off));
> clock_get(&end);
>
> *rt = clock_diff(&start, &end);
> @@ -401,7 +416,8 @@ static int do_memset(const struct function *r, struct bench_params *p,
>
> clock_get(&start);
> for (unsigned int i = 0; i < p->nr_loops; ++i)
> - fn(dst, i, p->size);
> + for (size_t off = 0; off < p->size; off += p->chunk_size)
> + fn(dst + off, i, min(p->chunk_size, p->size - off));
> clock_get(&end);
>
> *rt = clock_diff(&start, &end);
> --
> 2.43.5
>
Namhyung Kim <namhyung@kernel.org> writes: > On Wed, Jul 09, 2025 at 05:59:19PM -0700, Ankur Arora wrote: >> There can be a significant gap in memset/memcpy performance depending >> on the size of the region being operated on. >> >> With chunk-size=4kb: >> >> $ echo madvise > /sys/kernel/mm/transparent_hugepage/enabled >> >> $ perf bench mem memset -p 4kb -k 4kb -s 4gb -l 10 -f x86-64-stosq >> # Running 'mem/memset' benchmark: >> # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S) >> # Copying 4gb bytes ... >> >> 13.011655 GB/sec >> >> With chunk-size=1gb: >> >> $ echo madvise > /sys/kernel/mm/transparent_hugepage/enabled >> >> $ perf bench mem memset -p 4kb -k 1gb -s 4gb -l 10 -f x86-64-stosq >> # Running 'mem/memset' benchmark: >> # function 'x86-64-stosq' (movsq-based memset() in arch/x86/lib/memset_64.S) >> # Copying 4gb bytes ... >> >> 21.936355 GB/sec >> >> So, allow the user to specify the chunk-size. >> >> The default value is identical to the total size of the region, which >> preserves current behaviour. >> >> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com> > > Again, please update the documentation. With that, > > Reviewed-by: Namhyung Kim <namhyung@kernel.org> > Thanks! Will do. -- ankur
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