linux-kernel - Re: [dm-devel] Re: Ext3 sequential read performance drop 2.6.29 -> 2.6.30,2.6.31,...

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Date:	Tue, 3 Nov 2009 11:55:05 +0100
From:	Laurent CORBES <laurent.corbes@...rtjog.com>
To:	"NeilBrown" <neilb@...e.de>
Cc:	"device-mapper development" <dm-devel@...hat.com>,
	akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
	linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [dm-devel] Re: Ext3 sequential read performance drop 2.6.29 ->
  2.6.30,2.6.31,...

Hi all,

> >> > Hi all,
> >> >
> >> > While benchmarking some systems I discover a big sequential read
> >> performance
> >> > drop using ext3 on ~ big files. The drop seems to be introduced in
> >> 2.6.30. I'm
> >> > testing with 2.6.28.6 -> 2.6.29.6 -> 2.6.30.4 -> 2.6.31.3.
> >>
> >> Seems that large performance regressions aren't of interest to this
> >> list :(

Or +200MB/s is enough for a lot of people :)

> > No sure which list you mean, but dm-devel is for dm, not md.  We're also
> > seeing similarly massive performance drops with md and ext3/xfs as
> > already reported on the list.  Someone tracked it down to writeback
> > changes as usual, but there it got stuck.
> 
> I'm still looking - running some basic tests on 4 filesystems over
> half a dozen recent kernels to see what has been happening.
> 
> I have a suspicion that there a multiple problems.
> In particular, XFS has a strange degradation which was papered over
> by commit c8a4051c3731b.
> I'm beginning to wonder if it was caused by commit 17bc6c30cf6bf
> but I haven't actually tested that yet.

What is really strange is that from all the tests I did the raw md perfs never
dropped. only a few MB of diff between kernel (~2%). This is maybe related to
the way upper FS write datas on the md layer.

I'll make the tests on raw disks to see if there is some troubles here also. I
can also test with other raid layers. Is there any tuning/debug I
can make for you ? I can also setup a remote access to this system if needed.

Thanks.
-- 
Laurent Corbes - laurent.corbes@...rtjog.com
SmartJog SAS | Phone: +33 1 5868 6225 | Fax: +33 1 5868 6255 | www.smartjog.com
27 Blvd Hippolyte Marquès, 94200 Ivry-sur-Seine, France
A TDF Group company
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