blob: 2d88763915201b34de18daccffbc0800fe2aedaa [file] [log] [blame]
From c5e5c20e9088a442630a2ced4c183a879a4cdf2a Mon Sep 17 00:00:00 2001
From: Vincent Whitchurch <vincent.whitchurch@axis.com>
Date: Mon, 10 Aug 2020 15:34:04 +0200
Subject: [PATCH] perf bench mem: Always memset source before memcpy
commit 1beaef29c34154ccdcb3f1ae557f6883eda18840 upstream.
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>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index 0251dd348124..4864fc67d01b 100644
--- a/tools/perf/bench/mem-functions.c
+++ b/tools/perf/bench/mem-functions.c
@@ -222,12 +222,8 @@ 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);
@@ -236,6 +232,15 @@ 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)
@@ -251,11 +256,7 @@ 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)
--
2.27.0