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

Christian Borntraeger
2014-09-01T14:16:03Z

On 01/09/14 16:03, Christian Borntraeger wrote:
> 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.

Sorry, looked at the wrong inf file. The fedora driver does use MSI for serial and block.