linux-kernel - Re: bcache/dmcache/enhanceio bake-off

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Date:	Mon, 15 Apr 2013 09:55:39 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
	device-mapper development <dm-devel@...hat.com>,
	Kent Overstreet <koverstreet@...gle.com>,
	Amit Kale <akale@...c-inc.com>, ejt@...hat.com
Subject: Re: bcache/dmcache/enhanceio bake-off

On Sat, Apr 13 2013 at  3:33pm -0400,
Mike Snitzer <snitzer@...hat.com> wrote:

> On Sat, Apr 13 2013 at 12:09pm -0400,
> Joe Thornber <thornber@...hat.com> wrote:
> 
> > Hi Darrick,
> > 
> > On Thu, Apr 11, 2013 at 12:22:39AM -0700, Darrick J. Wong wrote:
> > > Hi all,
> > > 
> > > Lately I've been having some fun playing with bcache, dmcache, and enhanceio.
> > 
> > I pushed some tweaks to the mq policy today to my thin-dev tree.  They
> > show some improvements to these fio based tests.
> > 
> > In addition I've written a blog post trying to explain what's going on in dm-cache:
> > http://device-mapper.org/blog/2013/04/13/benchmarking-dm-cache-with-fio/
> 
> Darrick,
> 
> Joe has a few other dm-cache-target.c changes in his thin-dev branch
> that are required in order to realize the gains from his mq changes.  I
> haven't yet isolated which changes are important but if I just use the
> 3.9-rc6's dm-cache-tagret.c with thin-dev's mq changes I cannot
> reproduce the improved performance Joe mentions in his blog post.

I've now isolated the dm-cache-target.c commit in Joe's thin-dev that is
important to have in conjunction with the mq changes (from commit 7362f43a):

commit f134e6382a534dd3622c3850e4824ae5929885d9
Author: Joe Thornber <ejt@...hat.com>
Date:   Wed Mar 27 14:46:57 2013 +0000

    [dm-cache] Change the default migration_threshold to something more suitable.

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 8a4bcf3..f215307 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -1948,7 +1948,7 @@ static sector_t calculate_discard_block_size(sector_t cache_block_size,
 	return discard_block_size;
 }
 
-#define DEFAULT_MIGRATION_THRESHOLD (2048 * 100)
+#define DEFAULT_MIGRATION_THRESHOLD 2048
 
 static int cache_create(struct cache_args *ca, struct cache **result)
 {
--
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