Re: [Qemu-devel] Following up questions related to QEMU and I/O Thread

[Paolo Bonzini]

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.

Paolo