Re: Performance test result between virtio_pci MSI-X disable and enable

[Gleb Natapov <gleb@redhat.com>]

On Tue, Nov 23, 2010 at 08:20:19AM +0200, Avi Kivity wrote:
> On 11/23/2010 04:53 AM, lidong chen wrote:
> >Test method:
> >Send the same traffic load between virtio_pci MSI-X disable and
> >enable,and compare the cpu rate of host os.
> >I used the same version of virtio driver, only modify the msi-x option.
> >the host os version is 2.6.32.
> >the virtio dirver is from rhel6.
> >the guest version  os is 2.6.16.
> >
> >Test result:
> >with msi-x disable, the cpu rate of host os is 110%.
> >with msi-x enable, the cpu rate of host os is 140%.
> >
> ...
> 
> >Conclusion:
> >msi-x enable waste more cpu resource is caused by MSIX mask bit. In
> >older kernels program this bit twice
> >on every interrupt. and caused ept violation.
> >
> >So I think we should add a param to control this.with older kernels,
> >we should disable MSIX.
> >And I think this should deal by qemu.
> 
> There is now work in progress (by Sheng Yang) to speed up mask bit
> emulation, which should improve things.  Also, newer kernels don't
> hit the mask bit so hard.  You might try to backport the mask bit
> patches to your 2.6.16 guest.
> 
And IIRC we do have option to disable MSIX in qemu. I just don't
remember how it looks. Michael?

--
			Gleb.