Bad performance with XFS + 2.6.38 / 2.6.39

[Yann Dupont]

Le 12/12/2011 03:00, Xupeng Yun a écrit :
>
>
> On Mon, Dec 12, 2011 at 09:00, Dave Chinner <david at fromorbit.com
> <mailto:david at fromorbit.com>> 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 at univ-nantes.fr