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Re: Bad performance with XFS + 2.6.38 / 2.6.39

To: Yann Dupont <Yann.Dupont@xxxxxxxxxxxxxx>
Subject: Re: Bad performance with XFS + 2.6.38 / 2.6.39
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Wed, 21 Dec 2011 09:10:21 -0600
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4EF1A224.2070508@xxxxxxxxxxxxxx>
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On 12/21/2011 3:08 AM, Yann Dupont wrote:
> 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
>> _______________________________________________
>> xfs mailing list
>> xfs@xxxxxxxxxxx
>> http://oss.sgi.com/mailman/listinfo/xfs
> 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 ?

1.  What mailbox format are you using?  Is this a constant or variable?
2.  Is the Dovecot rev and config the same everywhere, before/after?
3.  Are Dovecot instances using NFS to access the XFS volumes?
4.  Is this a  Dovecot 2.x cluster with director and NFS storage?


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