Re: [Qemu-devel] [PATCH v2 00/15] SCSI s/g + SCSI migration + virtio-scsi

[Paolo Bonzini <pbonzini@redhat.com>]

On 01/30/2012 10:33 AM, Hu Tao wrote:
>> >  I cannot reproduce this with a 100G qcow2 image (created with
>> >  "qemu-img create scsi.qcow2 100G" just before launching the host),
>> >  with a partition starting at sector 2048 and extending to the end of
>> >  the disk.  mkfs (ext4) takes less than 1 minute and extends the
>> >  qcow2 file to a little less than 2 gigs.
>
> I've re-tested today, with host kernel 2.6.35.6-45.fc14.x86_64,
> 2.6.32-71.el6.x86_64, 3.1.0 and 3.3.0-rc1+, qemu version and guest
> configuration remain the same, including guest kernel. It apears
> that the problem appears only when the host kernel version is 3.1.0.

There are two parts in the bug:

1) I/O cancellation doesn't actually cancel anything on qcow2 (and maybe 
others) since the coroutine transition.  This makes exception handling 
basically unusable in the virtio-scsi guest driver.  I have been working 
on this but I don't have patches ready for testing yet.

2) Something unknown in the kernel is causing writes to take a longer 
time than usual.  This appears to be a problem only with 3.1.0 guest 
kernels.

I think we can wait until (1) causes problems elsewhere.  Thanks for 
testing!

Paolo