Hi
This is the clflushopt patch for the next merge window.
Mikulas
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
When testing the dm-writecache target on a real Optane-based persistent
memory, it turned out that explicit cache flushing using the clflushopt
instruction performs better than non-temporal stores for block sizes 1k,
2k and 4k.
This patch adds 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@xxxxxxxxxx>
---
drivers/md/dm-writecache.c | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)
Index: linux-2.6/drivers/md/dm-writecache.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-writecache.c 2020-04-29 18:09:53.599999000 +0200
+++ linux-2.6/drivers/md/dm-writecache.c 2020-04-29 18:22:36.139999000 +0200
@@ -1137,6 +1137,33 @@ static int writecache_message(struct dm_
return r;
}
+static void memcpy_flushcache_optimized(void *dest, void *source, size_t size)
+{
+ /*
+ * clufhsopt 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
+ */
+#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;
@@ -1162,7 +1189,7 @@ static void bio_copy_block(struct dm_wri
}
} else {
flush_dcache_page(bio_page(bio));
- memcpy_flushcache(data, buf, size);
+ memcpy_flushcache_optimized(data, buf, size);
}
bvec_kunmap_irq(buf, &flags);
--
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