From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755891Ab1HRPLT (ORCPT ); Thu, 18 Aug 2011 11:11:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:23280 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752490Ab1HRPLS (ORCPT ); Thu, 18 Aug 2011 11:11:18 -0400 Message-ID: <4E4D2B6D.1040908@redhat.com> Date: Thu, 18 Aug 2011 08:10:37 -0700 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:5.0) Gecko/20110707 Thunderbird/5.0 MIME-Version: 1.0 To: Sasha Levin CC: linux-kernel@vger.kernel.org, Rusty Russell , "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org Subject: Re: [PATCH] virtio-blk: Add stats VQ to collect information about devices References: <1313524071-27250-1-git-send-email-levinsasha928@gmail.com> <4E4C481A.5080205@redhat.com> <1313642283.22532.4.camel@lappy> In-Reply-To: <1313642283.22532.4.camel@lappy> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/17/2011 09:38 PM, Sasha Levin wrote: > On Wed, 2011-08-17 at 16:00 -0700, Avi Kivity wrote: > > On 08/16/2011 12:47 PM, Sasha Levin wrote: > > > This patch adds support for an optional stats vq that works similary to the > > > stats vq provided by virtio-balloon. > > > > > > The purpose of this change is to allow collection of statistics about working > > > virtio-blk devices to easily analyze performance without having to tap into > > > the guest. > > > > > > > > > > Why can't you get the same info from the host? i.e. read sectors? > > Some of the stats you can collect from the host, but some you can't. > > The ones you can't include all the timing statistics and the internal > queue statistics (read/write merges). Surely you can time the actual amount of time the I/O takes? It doesn't account for the virtio round-trip, but does it matter? Why is the merge count important for the host? > > The idea behind providing all of the stats on the stats vq (which is > basically what you see in '/dev/block/[device]/stats') is to give a > consistent snapshot of the state of the device. > > What can you do with it? -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.