Re: [Qemu-devel] [question] virtio-blk performance degradationhappened with virito-serial

Christian Borntraeger
2014-09-01T14:04:02Z

On 01/09/14 15:29, Paolo Bonzini wrote:
> Il 01/09/2014 15:22, Christian Borntraeger ha scritto:
>>>> If virtio-blk and virtio-serial share an IRQ, the guest operating system has to check each virtqueue for activity. Maybe there is some inefficiency doing that.
>>>> AFAIK virtio-serial registers 64 virtqueues (on 31 ports + console) even if everything is unused.
>>>
>>> That could be the case if MSI is disabled.
>>
>> Do the windows virtio drivers enable MSIs, in their inf file?
>
> It depends on the version of the drivers, but it is a reasonable guess
> at what differs between Linux and Windows. Haoyu, can you give us the
> output of lspci from a Linux guest?
>
> Paolo

Zhang Haoyu, which virtio drivers did you use?

I just checked the Fedora virtio driver. The INF file does not contain the MSI enablement as described in
http://msdn.microsoft.com/en-us/library/windows/hardware/ff544246%28v=vs.85%29.aspx
That would explain the performance issues - given that the link information is still true.

Christian