Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH] x86: introduce memcpy_flushcache_clflushopt | Date | Sat, 18 Apr 2020 13:27:53 +0000 |
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From: Mikulas Patocka > Sent: 17 April 2020 13:47 ... > Index: linux-2.6/drivers/md/dm-writecache.c > =================================================================== > --- linux-2.6.orig/drivers/md/dm-writecache.c 2020-04-17 14:06:35.139999000 +0200 > +++ linux-2.6/drivers/md/dm-writecache.c 2020-04-17 14:06:35.129999000 +0200 > @@ -1166,7 +1166,10 @@ static void bio_copy_block(struct dm_wri > } > } else { > flush_dcache_page(bio_page(bio)); > - memcpy_flushcache(data, buf, size); > + if (likely(size > 512)) > + memcpy_flushcache_clflushopt(data, buf, size); > + else > + memcpy_flushcache(data, buf, size);
Hmmm... have you looked at how long clflush actually takes? It isn't too bad if you just do a small number, but using it to flush large buffers can be very slow.
I've an Ivy bridge system where the X-server process requests the frame buffer be flushed out every 10 seconds (no idea why). With my 2560x1440 monitor this takes over 3ms.
This really needs a cond_resched() every few clflush instructions.
David
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