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Re: Bad performance with XFS + 2.6.38 / 2.6.39

To: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: Bad performance with XFS + 2.6.38 / 2.6.39
From: Yann Dupont <Yann.Dupont@xxxxxxxxxxxxxx>
Date: Wed, 04 Jan 2012 14:06:15 +0100
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, stan@xxxxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20120104123331.GA12204@xxxxxxxxxxxxx>
References: <CACaf2ab-YjXAFm767MmRU5iuOmvkqQW3ZTfQewD5SGvF-opgYQ@xxxxxxxxxxxxxx> <4EF1A224.2070508@xxxxxxxxxxxxxx> <4EF1F6DD.8020603@xxxxxxxxxxxxxxxxx> <4EF21DD2.3060004@xxxxxxxxxxxxxx> <20111221222623.GF23662@dastard> <4EF2F702.4050902@xxxxxxxxxxxxxx> <4EF30E5D.7060608@xxxxxxxxxxxxxx> <4F0181A2.5010505@xxxxxxxxxxxxxx> <20120102203543.GP23662@dastard> <4F02BA35.9040909@xxxxxxxxxxxxxx> <20120104123331.GA12204@xxxxxxxxxxxxx>
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On 04/01/2012 13:33, Christoph Hellwig wrote:
On Tue, Jan 03, 2012 at 09:20:05AM +0100, Yann Dupont wrote:
As it is, I can't see any material difference between the traces.
both reads and writes are taking the same amount of time to service,
so I don't think there's any problem here.

ok,

I do recall that some years ago that we changed one of the ways we

Do you recall exactly what some years ago means ? Is this post 2.6.26 era ?

The only thing that I remember is Jens switching xfs_buf_wait_unpin from
schedule to io_schedule in "block: remove per-queue plugging", which
went into Linux 2.6.39.  With this processed that wait for buffers to
be unpinned now count towards the load average.


Ok, that's probably the root cause. As I already said, I don't experience performance regression right now.

Thanks a lot for the explaination.

Cheers,



--
Yann Dupont - Service IRTS, DSI Université de Nantes
Tel : 02.53.48.49.20 - Mail/Jabber : Yann.Dupont@xxxxxxxxxxxxxx

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