Patch "perf bench mem: Always memset source before memcpy" has been added to the 4.14-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    perf bench mem: Always memset source before memcpy

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     perf-bench-mem-always-memset-source-before-memcpy.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit e871fe93689588f74120d01596c6bc30ced00986
Author: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
Date:   Mon Aug 10 15:34:04 2020 +0200

    perf bench mem: Always memset source before memcpy
    
    [ Upstream commit 1beaef29c34154ccdcb3f1ae557f6883eda18840 ]
    
    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@xxxxxxxx>
    Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
    Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
    Cc: Mark Rutland <mark.rutland@xxxxxxx>
    Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
    Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
    Cc: kernel@xxxxxxxx
    Link: http://lore.kernel.org/lkml/20200810133404.30829-1-vincent.whitchurch@xxxxxxxx
    Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/tools/perf/bench/mem-functions.c b/tools/perf/bench/mem-functions.c
index 0251dd348124a..4864fc67d01b5 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)