Bad performance with XFS + 2.6.38 / 2.6.39

[Yann Dupont]

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 at univ-nantes.fr