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Re: Bad performance with XFS + 2.6.38 / 2.6.39

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Subject: Re: Bad performance with XFS + 2.6.38 / 2.6.39
From: Yann Dupont <Yann.Dupont@xxxxxxxxxxxxxx>
Date: Wed, 21 Dec 2011 10:08:52 +0100
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Le 12/12/2011 03:00, Xupeng Yun a écrit :


On Mon, Dec 12, 2011 at 09:00, Dave Chinner <david@xxxxxxxxxxxxx
<mailto:david@xxxxxxxxxxxxx>> wrote:

    Oh, of course, now I remember what the problem is - it's a locking
    issue that was fixed in 3.0.11, 3.1.5 and 3.2-rc1.


Got it, thanks.

--
Xupeng Yun
http://about.me/xupeng


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I'm seeing more or less the same here.

Generally speaking XFS code in recent kernels seems to decrease CPU usage and be faster, which is a very good thing (good works, guy). But...

On two particular server, with recent kernels, I experience a much higher load than expected, but it's very hard to tell what's wrong. The system seems more in I/O wait. Older kernels (2.6.32.xx and 2.6.26.xx) gives better results.

Following this thread, I thought I have the same problems, but it's probably not the case, as I have tested 2.6.38.xx, 3.0.13, 3.1.5 with same results.

Thoses servers are mail (dovecot) servers, with lots of simultaneous imap clients (5000+) an lots of simultaneous message delivery.

These are linux-vservers, on top of LVM volumes. The storage is SAN with 15k RPM SAS drives (and battery backup).

I know barriers were disabled in older kernels, so with recents kernels, XFS volumes were mounted with nobarrier.

As those servers are critical for us, I can't really test, hardly give you more precise numbers, and I don't know how to accurately reproduce this platform to test what's wrong. I know this is NOT a precise bug report and it won't help much.

All I can say IS :

- read operations seems no slower with recent kernels, backups take approximatively the same time ; - I'd say (but I have no proof) that delivery of new mails takes more time and is more synchronous than before, like nobarrier have no effect.

Does this ring a bell to some of you ?

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

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