The patch titled
Subject: lib/test_vmalloc: switch to prandom_u32()
has been added to the -mm mm-unstable branch. Its filename is
lib-test_vmalloc-switch-to-prandom_u32.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/lib-test_vmalloc-switch-to-prandom_u32.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Uladzislau Rezki (Sony)" <urezki@xxxxxxxxx>
Subject: lib/test_vmalloc: switch to prandom_u32()
Date: Tue, 7 Jun 2022 11:34:49 +0200
A get_random_bytes() function can cause a high contention if it is called
across CPUs simultaneously. Because it shares one lock per all CPUs:
<snip>
class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg
&crng->lock: 663145 665886 0.05 8.85 261966.66 0.39 7188152 13731279 0.04 11.89 2181582.30 0.16
-----------
&crng->lock 307835 [<00000000acba59cd>] _extract_crng+0x48/0x90
&crng->lock 358051 [<00000000f0075abc>] _crng_backtrack_protect+0x32/0x90
-----------
&crng->lock 234241 [<00000000f0075abc>] _crng_backtrack_protect+0x32/0x90
&crng->lock 431645 [<00000000acba59cd>] _extract_crng+0x48/0x90
<snip>
Switch from the get_random_bytes() to prandom_u32() that does not have any
internal contention when a random value is needed for the tests.
The reason is to minimize CPU cycles introduced by the test-suite itself
from the vmalloc performance metrics.
Link: https://lkml.kernel.org/r/20220607093449.3100-6-urezki@xxxxxxxxx
Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
lib/test_vmalloc.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
--- a/lib/test_vmalloc.c~lib-test_vmalloc-switch-to-prandom_u32
+++ a/lib/test_vmalloc.c
@@ -74,12 +74,13 @@ test_report_one_done(void)
static int random_size_align_alloc_test(void)
{
- unsigned long size, align, rnd;
+ unsigned long size, align;
+ unsigned int rnd;
void *ptr;
int i;
for (i = 0; i < test_loop_count; i++) {
- get_random_bytes(&rnd, sizeof(rnd));
+ rnd = prandom_u32();
/*
* Maximum 1024 pages, if PAGE_SIZE is 4096.
@@ -150,7 +151,7 @@ static int random_size_alloc_test(void)
int i;
for (i = 0; i < test_loop_count; i++) {
- get_random_bytes(&n, sizeof(i));
+ n = prandom_u32();
n = (n % 100) + 1;
p = vmalloc(n * PAGE_SIZE);
@@ -294,14 +295,14 @@ pcpu_alloc_test(void)
for (i = 0; i < 35000; i++) {
unsigned int r;
- get_random_bytes(&r, sizeof(i));
+ r = prandom_u32();
size = (r % (PAGE_SIZE / 4)) + 1;
/*
* Maximum PAGE_SIZE
*/
- get_random_bytes(&r, sizeof(i));
- align = 1 << ((i % 11) + 1);
+ r = prandom_u32();
+ align = 1 << ((r % 11) + 1);
pcpu[i] = __alloc_percpu(size, align);
if (!pcpu[i])
@@ -396,7 +397,7 @@ static void shuffle_array(int *arr, int
int i, j;
for (i = n - 1; i > 0; i--) {
- get_random_bytes(&rnd, sizeof(rnd));
+ rnd = prandom_u32();
/* Cut the range. */
j = rnd % i;
_
Patches currently in -mm which might be from urezki@xxxxxxxxx are
mm-vmalloc-make-link_va-unlink_va-common-to-different-rb_root.patch
mm-vmalloc-extend-__alloc_vmap_area-with-extra-arguments.patch
mm-vmalloc-initialize-vas-list-node-after-unlink.patch
mm-vmalloc-extend-__find_vmap_area-with-one-more-argument.patch
lib-test_vmalloc-switch-to-prandom_u32.patch
