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


From: Wei Li
Subject: Re: [Qemu-devel] Following up questions related to QEMU and I/O Thread
Date: Mon, 15 Apr 2019 10:34:56 -0700
User-agent: Microsoft-MacOutlook/10.15.0.190115

Hi @Paolo Bonzini & @Stefan Hajnoczi,

Would you please help confirm whether @Paolo Bonzini's multiqueue feature 
change will benefit virtio-scsi or not? Thanks!

@Stefan Hajnoczi,
I also spent some time on exploring the virtio-scsi multi-queue features via 
num_queues parameter as below, here are what we found:

1. Increase number of Queues from one to the same number as CPU will get better 
IOPS increase.
2. Increase number of Queues to the number (e.g. 8) larger than the number of 
vCPU (e.g. 2) can get even better IOPS increase.

In addition, It seems Qemu can get better IOPS while the attachment uses more 
queues than the number of vCPU, how could it possible? Could you please help us 
better understand the behavior? Thanks a lot!


Host CPU Configuration:
CPU(s):                2
Thread(s) per core:    2
Core(s) per socket:    1
Socket(s):             1

Commands for multi queue Setup:
(QEMU)  device_add driver=virtio-scsi-pci num_queues=1 id=test1
(QEMU)  device_add driver=virtio-scsi-pci num_queues=2 id=test2
(QEMU)  device_add driver=virtio-scsi-pci num_queues=4 id=test4
(QEMU)  device_add driver=virtio-scsi-pci num_queues=8 id=test8


Result:
        |  8 Queues   |  4 Queues     |      2 Queues    |      Single Queue
IOPS    |   +29%         |      27%           |        11%           |      
Baseline

Thanks,
Wei

On 4/5/19, 2:09 PM, "Wei Li" <address@hidden> wrote:

    Thanks Stefan for your quick response!
    
    Hi Paolo,
    Could you please send us a link related to the multiqueue feature which you 
are working on so that we could start getting some details about the feature.
    
    Thanks again,
    Wei 
    
    On 4/1/19, 3:54 AM, "Stefan Hajnoczi" <address@hidden> wrote:
    
        On Fri, Mar 29, 2019 at 08:16:36AM -0700, Wei Li wrote:
        > 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? 
        
        Paolo last worked on this code, so he may be able to send you a link.
        
        Stefan
        
    





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