From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Subject: Re: [Qemu-devel] [question] virtio-blk performance degradationhappened with virito-serial Date: Mon, 01 Sep 2014 16:03:57 +0200 Message-ID: <54047CCD.4000101@de.ibm.com> References: <201408291545282753855@sangfor.com>, <20140829143849.GA8909@grmbl.mre>, <201409012038178763909@sangfor.com> <201409012052442706397@sangfor.com> <5404701F.5070302@de.ibm.com> <540470CD.9060800@redhat.com> <5404731A.8020405@de.ibm.com> <5404749F.7050606@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: qemu-devel , kvm To: Paolo Bonzini , Zhang Haoyu , Amit Shah Return-path: Received: from e06smtp10.uk.ibm.com ([195.75.94.106]:60625 "EHLO e06smtp10.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751665AbaIAOEC (ORCPT ); Mon, 1 Sep 2014 10:04:02 -0400 Received: from /spool/local by e06smtp10.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 1 Sep 2014 15:04:00 +0100 Received: from b06cxnps3075.portsmouth.uk.ibm.com (d06relay10.portsmouth.uk.ibm.com [9.149.109.195]) by d06dlp02.portsmouth.uk.ibm.com (Postfix) with ESMTP id DE1E92190063 for ; Mon, 1 Sep 2014 15:03:39 +0100 (BST) Received: from d06av09.portsmouth.uk.ibm.com (d06av09.portsmouth.uk.ibm.com [9.149.37.250]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id s81E3w1R43909130 for ; Mon, 1 Sep 2014 14:03:58 GMT Received: from d06av09.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av09.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s81E3v5s012360 for ; Mon, 1 Sep 2014 08:03:58 -0600 In-Reply-To: <5404749F.7050606@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 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