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dm writecache: improve performance on DDR persistent memory (Optane)

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When testing the dm-writecache target on a real DDR persistent memory
(Intel Optane), it turned out that explicit cache flushing using the
clflushopt instruction performs better than non-temporal stores for
block sizes 1k, 2k and 4k.

The dm-writecache target is singlethreaded (all the copying is done
while holding the writecache lock), so it benefits from clwb, see:
http://lore.kernel.org/r/alpine.LRH.2.02.2004160411460.7833@file01.intranet.prod.int.rdu2.redhat.com

Add a new function memcpy_flushcache_optimized() that tests if
clflushopt is present - and if it is, we use it instead of
memcpy_flushcache.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Mikulas Patocka 2020-04-29 12:30:03 -04:00 committed by Mike Snitzer
parent 499c18045e
commit 48338daaa0
1 changed files with 37 additions and 1 deletions
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38
drivers/md/dm-writecache.c
View File

@ -1139,6 +1139,42 @@ static int writecache_message(struct dm_target *ti, unsigned argc, char **argv,
return r;
}
static void memcpy_flushcache_optimized(void *dest, void *source, size_t size)
{
/*
* clflushopt performs better with block size 1024, 2048, 4096
* non-temporal stores perform better with block size 512
*
* block size 512 1024 2048 4096
* movnti 496 MB/s 642 MB/s 725 MB/s 744 MB/s
* clflushopt 373 MB/s 688 MB/s 1.1 GB/s 1.2 GB/s
*
* We see that movnti performs better for 512-byte blocks, and
* clflushopt performs better for 1024-byte and larger blocks. So, we
* prefer clflushopt for sizes >= 768.
*
* NOTE: this happens to be the case now (with dm-writecache's single
* threaded model) but re-evaluate this once memcpy_flushcache() is
* enabled to use movdir64b which might invalidate this performance
* advantage seen with cache-allocating-writes plus flushing.
*/
#ifdef CONFIG_X86
if (static_cpu_has(X86_FEATURE_CLFLUSHOPT) &&
likely(boot_cpu_data.x86_clflush_size == 64) &&
likely(size >= 768)) {
do {
memcpy((void *)dest, (void *)source, 64);
clflushopt((void *)dest);
dest += 64;
source += 64;
size -= 64;
} while (size >= 64);
return;
}
#endif
memcpy_flushcache(dest, source, size);
}
static void bio_copy_block(struct dm_writecache *wc, struct bio *bio, void *data)
{
void *buf;
@ -1164,7 +1200,7 @@ static void bio_copy_block(struct dm_writecache *wc, struct bio *bio, void *data
}
} else {
flush_dcache_page(bio_page(bio));
memcpy_flushcache(data, buf, size);
memcpy_flushcache_optimized(data, buf, size);
}
bvec_kunmap_irq(buf, &flags);