Re: [Qemu-devel] [PATCH] raw-posix: Linearize direct I/O on Linux NFS

[Stefan Hajnoczi]

On Sat, Apr 16, 2011 at 12:00 AM, Anthony Liguori <address@hidden> wrote:
> 3) We have no way to detect when we no longer need a work around which makes
> (2) really unappealing.

I agree.

> 4) That leaves us with:
>    a) waiting for NFS to get fixed properly and just living with worse
> performance on older kernels
>
>    b) having a user-tunable switch to enable bouncing
>
> I really dislike the idea of (b) because we're stuck with it forever and
> it's yet another switch for people to mistakenly depend on.

The user-tunable switch is potentially interesting for performance
troubleshooting.  We have seen another file system which has issues
with vectored direct I/O.  It would have been much easier to identify
the problem by telling the user "Try running it with linearize=on and
see if it makes a difference".

But let's try harder on linux-nfs.

Stefan