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| author | Uladzislau Rezki (Sony) <urezki@gmail.com> | 2022-06-07 11:34:49 +0200 |
|---|---|---|
| committer | akpm <akpm@linux-foundation.org> | 2022-07-03 18:08:42 -0700 |
| commit | 5e21f2d577cf174ced5fe9bdff67dcb70190d9f8 (patch) | |
| tree | 9a6cc21584d6c86e6e5df1bf484072f803fdedb2 /lib/test_vmalloc.c | |
| parent | 899c6efe58dbe8cb9768057ffc206d03e5a89ce8 (diff) | |
| download | lwn-5e21f2d577cf174ced5fe9bdff67dcb70190d9f8.tar.gz lwn-5e21f2d577cf174ced5fe9bdff67dcb70190d9f8.zip | |
lib/test_vmalloc: switch to prandom_u32()
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@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'lib/test_vmalloc.c')
| -rw-r--r-- | lib/test_vmalloc.c | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c index cf41fd6df42a..4f2f2d1bac56 100644 --- a/lib/test_vmalloc.c +++ b/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 n) 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; |