From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S937865Ab0CPMaF (ORCPT ); Tue, 16 Mar 2010 08:30:05 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:48911 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S937852Ab0CPMaB (ORCPT ); Tue, 16 Mar 2010 08:30:01 -0400 Date: Tue, 16 Mar 2010 13:29:03 +0100 From: Ingo Molnar To: Avi Kivity Cc: "Zhang, Yanmin" , Peter Zijlstra , Sheng Yang , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Marcelo Tosatti , oerg Roedel , Jes Sorensen , Gleb Natapov , Zachary Amsden , ziteng.huang@intel.com Subject: Re: [PATCH] Enhance perf to collect KVM guest os statistics from host side Message-ID: <20100316122903.GA8831@elte.hu> References: <20100316072449.GB11881@elte.hu> <4B9F4D74.4090403@redhat.com> <20100316095336.GI7961@elte.hu> <4B9F59DE.1060008@redhat.com> <20100316102052.GC10069@elte.hu> <4B9F603B.4080004@redhat.com> <20100316105021.GA14344@elte.hu> <4B9F671D.5060001@redhat.com> <20100316112500.GA5337@elte.hu> <4B9F77E7.2060101@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B9F77E7.2060101@redhat.com> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Avi Kivity wrote: > On 03/16/2010 01:25 PM, Ingo Molnar wrote: > > > >>I haven't followed vmchannel closely, but I think it is. vmchannel is > >>terminated in qemu on the host side, not in the host kernel. So perf would > >>need to connect to qemu. > >Hm, that sounds rather messy if we want to use it to basically expose kernel > >functionality in a guest/host unified way. Is the qemu process discoverable in > >some secure way? > > We know its pid. How do i get a list of all 'guest instance PIDs', and what is the way to talk to Qemu? > > Can we trust it? > > No choice, it contains the guest address space. I mean, i can trust a kernel service and i can trust /proc/kallsyms. Can perf trust a random process claiming to be Qemu? What's the trust mechanism here? > > Is there some proper tooling available to do it, or do we have to push it > > through 2-3 packages to get such a useful feature done? > > libvirt manages qemu processes, but I don't think this should go through > libvirt. qemu can do this directly by opening a unix domain socket in a > well-known place. So Qemu has never run into such problems before? ( Sounds weird - i think Qemu configuration itself should be done via a unix domain socket driven configuration protocol as well. ) > >( That is the general thought process how many cross-discipline useful > > desktop/server features hit the bit bucket before having had any chance of > > being vetted by users, and why Linux sucks so much when it comes to feature > > integration and application usability. ) > > You can't solve everything in the kernel, even with a well populated tools/. Certainly not, but this is a technical problem in the kernel's domain, so it's a fair (and natural) expectation to be able to solve this within the kernel project. Ingo