7 messages in com.xensource.lists.xen-develRe: [Xen-devel] [PATCH][RFC] open HVM...
FromSent OnAttachments
Rik van Riel28 Jul 2006 00:05.patch
Rik van Riel28 Jul 2006 10:02 
Rik van Riel28 Jul 2006 13:21 
Christian Limpach28 Jul 2006 17:44 
Rik van Riel30 Jul 2006 15:45 
Rik van Riel02 Aug 2006 16:25 
Christian Limpach04 Aug 2006 02:29 
Subject:Re: [Xen-devel] [PATCH][RFC] open HVM backing storage with O_SYNC
From:Christian Limpach (chri@gmail.com)
Date:07/28/2006 05:44:36 PM
List:com.xensource.lists.xen-devel

On 7/28/06, Rik van Riel <ri@redhat.com> wrote:

Rik van Riel wrote:

Rik van Riel wrote:

Any comments on this patch?

I got some comments from Alan, who would like to see this behaviour tunable with hdparm from inside the guest. This requires larger qemu changes though, to be specific an ->fsync callback into each of the backing store drivers, so that is something for the qemu mailing list.

Considering the AIO-based development going on in the qemu community, I think we should stick with the O_SYNC band-aid. The idea Alan described would just be a fancier band-aid.

Another possibility would be to integrate blktap/tapdisk into qemu which will provide asynchronous completion events and hides the immediate AIO interaction from qemu. This should also make using qemu inside a stub domain easier since the code to talk to tapdisk will be very similar to the blkfront code. Also, this is somewhat required to use tap devices for HVM domains, the alternative of using blkfront within dom0 to export the device for qemu to use doesn't sound too appealing.

Do you fancy looking into this?

The current bottleneck seems to be that MAX_MULT_COUNT is only 16.

Upon closer inspection of the code, this seems to not be the case for LBA48 transfers.

Any other ideas what could be the bottleneck then?

christian