From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: Performance test result between virtio_pci MSI-X disable and enable Date: Tue, 23 Nov 2010 08:42:14 +0200 Message-ID: <20101123064213.GO7948@redhat.com> References: <4CEB5D23.6040809@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: lidong chen , mst@redhat.com, aliguori@us.ibm.com, rusty@rustcorp.com.au, kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:10307 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751722Ab0KWGmZ (ORCPT ); Tue, 23 Nov 2010 01:42:25 -0500 Content-Disposition: inline In-Reply-To: <4CEB5D23.6040809@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 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.