Bad performance with XFS + 2.6.38 / 2.6.39

[Christoph Hellwig]

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.