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

[Wei Li]

Thanks Stefan and Paolo for your response and advice!

Hi Paolo,

As to the virtio-scsi batch I/O submission feature in QEMU which you mentioned, 
is this feature turned on by default in QEMU 2.9 or there is a tunable 
parameters to turn on/off the feature?

Thanks,
Wei

On 4/26/19, 1:14 AM, "Paolo Bonzini" <address@hidden> 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.