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

[Wei Li]

Thanks Stefan for your reply and guidance!

We spent some time on exploring the multiple I/O Threads approach per your 
feedback. Based on the perf measurement data, we did see some IOPS improvement 
for multiple volumes, which is great. :)

In addition, IOPS for single Volume will still be a bottleneck, it seems like 
multiqueue block layer feature which Paolo is working on may be able to help 
improving the IOPS for single volume.

@Paolo, @Stefan, 
Would you mind sharing the multiqueue feature code branch with us? So that we 
could get some rough idea about this feature and maybe start doing some 
exploration? 

Thanks a lot!
Wei

On 3/5/19, 9:29 AM, "Stefan Hajnoczi" <address@hidden> wrote:

    On Mon, Mar 04, 2019 at 09:33:26AM -0800, Wei Li wrote:
    > While @Stefan mentioned about additional iothread object support of 
virtio-blk, Is the feature also supported by virtio-scsi? I am trying to 
exploring the perf multiple IO threads / per VM via followings:
    > QMP setup example to create 2 io threads in QEMU, one io thread per 
device:
    > 
    > (QEMU) object-add qom-type=iothread id=iothread0
    > 
    > (QEMU) object-add qom-type=iothread id=iothread1
    > 
    >  
    > 
    > (QEMU) device_add driver=virtio-scsi-pci id=test0 iothread=iothread0
    > 
    > (QEMU) device_add driver=virtio-scsi-pci id=test1 iothread=iothread1
    > 
    >  
    > 
    > (QEMU) device_add driver=scsi-block drive=none0 id=v0 bus=test0.0
    > 
    > (QEMU) device_add driver=scsi-block drive=none1 id=v1 bus=test1.0
    
    Yes, each virtio-scsi-pci device can be assigned to an iothread.
    
    > You mentioned about the multi-queue devices feature, it seems like the 
multi-queue feature will help improve the IOPS of  single Device. Could you 
please provide more details?
    > What’s the current plan of support multi-queue device? Which release will 
include the support or it has already been included in any existing release 
newer than 2.9?
    > Is there any feature branch which I would get more details about the code 
and in progress status?
    
    I have CCed Paolo, who has worked on multiqueue block layer support in
    QEMU.  This feature is not yet complete.
    
    The virtio-scsi device also supports multiqueue, but the QEMU block
    layer will still be a single queue.
    
    Stefan