Re: Possible performance problem introduced between kernel 2.6.15 and 2.6.17 on xfs code

[Francesco Degrassi <francesco.degrassi@emaze.net>]

Hi Iustin,
i tried and it and indeed the performance problem does not manifest if i
mount the xfs filesystem with the -o nobarrier option. Seems like we are
a little bit closer to the real problem now.
The code in gnomevfs-copy calls fadvice POSIX_FADV_DONTNEED (in
gnome_vfs_forget_cache) and disabling this behaviour gets back normal
performance, so it has something to do with that.

Thanks for your help

Francesco


Iustin Pop wrote:
> On Wed, Dec 27, 2006 at 07:03:45PM +0100, Francesco Degrassi wrote:
>> I tried ext2, ext3, jfs, reiser3, vfat and the problem does not show up.
>> Anyway i discovered that if i create a regular file in an XFS partition,
>> create an XFS filesystem on it as if it was a regular block device, and
>> mount it with the loop device, the problem does NOT manifest.
>> So it seems to affect XFS filesystems on regular block devices only ?
>> I'm confused.
> 
> This is probably not related, but I remember that barriers were added
> sometime between 2.6.15 and 2.6.17 and probably barriers are not enabled
> on a loop filesystem. Maybe the gnome vfs thing does some sync which
> force flushes or such. I'm no expert, just guessing.
> 
> Just to invalidate this (probably wrong) guess, could you try to mount
> /tmp with "-o nobarrier" and re-test?
> 
> Iustin, who wishes md raid1 would support barriers.