[Lguest] Virtio block problems on newer kernels

[Sakari Ailus]

Hi Jens,

Thank you for your swift reply.

On Sun, May 25, 2014 at 10:15:41AM -0600, Jens Axboe wrote:
> >>> commit 1cf7e9c68fe84248174e998922b39e508375e7c1
> >>> Author: Jens Axboe <axboe at kernel.dk>
> >>> Date:   Fri Nov 1 10:52:52 2013 -0600
> >>> 
> >>>    virtio_blk: blk-mq support
> >> 
> >> Interesting!
> >> 
> >>>    Switch virtio-blk from the dual support for old-style requests and bios
> >>>    to use the block-multiqueue.
> >>> 
> >>>    Acked-by: Asias He <asias at redhat.com>
> >>>    Signed-off-by: Jens Axboe <axboe at kernel.dk>
> >>>    Signed-off-by: Christoph Hellwig <hch at lst.de>
> >>> 
> >>> Erratic block i/o behaviour begin when that patch is applied to the guest
> >>> kernel. I wonder if someone else has seen this. I can reproduce it
> >>> relatively easily by running bonnie++ in a guest:
> >>> 
> >>>    bonnie++ -n 0 -s 256M -r 10 -b
> >>> 
> >>> I'm using an up-to-date lguest launcher.
> >> 
> >> I cannot reproduce this under qemu (that's how I run my 32-bit host
> >> these days) with Linus' latest.  Of course, if the issue is that we have
> >> a race and performance has increased to trigger it, it's not surprising.
> > 
> > The I/O performance might rather be less than on your Qemu virtual
> > machine in this case --- this is an Athlon XP host with virtio block
> > devices backed by RAID 0 + luks + lvm without hardware acceleration for
> > encryption.
> 
> Can you try with this applied?
> 
> 
> http://git.kernel.dk/?p=linux-block.git;a=commit;h=0c29e93eae8a7f703e463c7b38ebc85d8718cae2

I can confirm this patch indeed fixes the problem I've been seeing. It'd be
nice to have this applied to the stable series kernels as well.

Cc Ming.

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus at iki.fi	XMPP: sailus at retiisi.org.uk