Thanks Stefan!
Does this mean the performance could be improved via adding Batch I/O
submission support in Guest driver side which will be able to reduce the number
of virtqueue kicks?
Thanks,
Wei
On 4/29/19, 6:40 AM, "Stefan Hajnoczi" <stefa...@redhat.com> wrote:
On Fri, Apr 26, 2019 at 10:14:16AM +0200, Paolo Bonzini wrote:
> On 23/04/19 14:04, Stefan Hajnoczi wrote:
> >> In addition, does Virtio-scsi support Batch I/O Submission feature
> >> which may be able to increase the IOPS via reducing the number of
> >> system calls?
> >
> > I don't see obvious batching support in drivers/scsi/virtio_scsi.c.
> > The Linux block layer supports batching but I'm not sure if the SCSI
> > layer does.
>
> I think he's referring to QEMU, in which case yes, virtio-scsi does
> batch I/O submission. See virtio_scsi_handle_cmd_req_prepare and
> virtio_scsi_handle_cmd_req_submit in hw/scsi/virtio-scsi.c, they do
> blk_io_plug and blk_io_unplug in order to batch I/O requests from QEMU
> to the host kernel.
This isn't fully effective since the guest driver kicks once per
request. Therefore QEMU-level batching you mentioned only works if QEMU
is slower at handling virtqueue kicks than the guest is at submitting
requests.
I wonder if this is something that can be improved.
Stefan
