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authorVincent Whitchurch <vincent.whitchurch@axis.com>2020-08-10 15:34:04 +0200
committerArnaldo Carvalho de Melo <acme@redhat.com>2020-08-13 09:34:26 -0300
commit1beaef29c34154ccdcb3f1ae557f6883eda18840 (patch)
tree85021c2a79253a9aa2c2fc703a821ce93b7cbea0 /tools
parentd566a9c2d482640abf5e602957b44e7b3bbe858d (diff)
perf bench mem: Always memset source before memcpy
For memcpy, the source pages are memset to zero only when --cycles is used. This leads to wildly different results with or without --cycles, since all sources pages are likely to be mapped to the same zero page without explicit writes. Before this fix: $ export cmd="./perf stat -e LLC-loads -- ./perf bench \ mem memcpy -s 1024MB -l 100 -f default" $ $cmd 2,935,826 LLC-loads 3.821677452 seconds time elapsed $ $cmd --cycles 217,533,436 LLC-loads 8.616725985 seconds time elapsed After this fix: $ $cmd 214,459,686 LLC-loads 8.674301124 seconds time elapsed $ $cmd --cycles 214,758,651 LLC-loads 8.644480006 seconds time elapsed Fixes: 47b5757bac03c338 ("perf bench mem: Move boilerplate memory allocation to the infrastructure") Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: kernel@axis.com Link: http://lore.kernel.org/lkml/20200810133404.30829-1-vincent.whitchurch@axis.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools')
-rw-r--r--tools/perf/bench/mem-functions.c21
1 files changed, 11 insertions, 10 deletions
diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index 9235b76501be..19d45c377ac1 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -223,12 +223,8 @@ static int bench_mem_common(int argc, const char **argv, struct bench_mem_info *
return 0;
}
-static u64 do_memcpy_cycles(const struct function *r, size_t size, void *src, void *dst)
+static void memcpy_prefault(memcpy_t fn, size_t size, void *src, void *dst)
{
- u64 cycle_start = 0ULL, cycle_end = 0ULL;
- memcpy_t fn = r->fn.memcpy;
- int i;
-
/* Make sure to always prefault zero pages even if MMAP_THRESH is crossed: */
memset(src, 0, size);
@@ -237,6 +233,15 @@ static u64 do_memcpy_cycles(const struct function *r, size_t size, void *src, vo
* to not measure page fault overhead:
*/
fn(dst, src, size);
+}
+
+static u64 do_memcpy_cycles(const struct function *r, size_t size, void *src, void *dst)
+{
+ u64 cycle_start = 0ULL, cycle_end = 0ULL;
+ memcpy_t fn = r->fn.memcpy;
+ int i;
+
+ memcpy_prefault(fn, size, src, dst);
cycle_start = get_cycles();
for (i = 0; i < nr_loops; ++i)
@@ -252,11 +257,7 @@ static double do_memcpy_gettimeofday(const struct function *r, size_t size, void
memcpy_t fn = r->fn.memcpy;
int i;
- /*
- * We prefault the freshly allocated memory range here,
- * to not measure page fault overhead:
- */
- fn(dst, src, size);
+ memcpy_prefault(fn, size, src, dst);
BUG_ON(gettimeofday(&tv_start, NULL));
for (i = 0; i < nr_loops; ++i)