Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755125Ab0DNKUX (ORCPT ); Wed, 14 Apr 2010 06:20:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:27899 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752542Ab0DNKUV (ORCPT ); Wed, 14 Apr 2010 06:20:21 -0400 Message-ID: <4BC596C5.7020507@redhat.com> Date: Wed, 14 Apr 2010 13:19:49 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Sheng Yang CC: "Zhang, Yanmin" , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Marcelo Tosatti , oerg Roedel , Jes Sorensen , Gleb Natapov , Zachary Amsden , zhiteng.huang@intel.com, tim.c.chen@intel.com, Arnaldo Carvalho de Melo Subject: Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os statistics from host side References: <1902387910.2078.435.camel@ymzhang.sh.intel.com> <201004141743.32393.sheng@linux.intel.com> <4BC5919E.1010400@redhat.com> <201004141814.19330.sheng@linux.intel.com> In-Reply-To: <201004141814.19330.sheng@linux.intel.com> 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 Content-Length: 1444 Lines: 36 On 04/14/2010 01:14 PM, Sheng Yang wrote: > >> I wouldn't like to depend on model specific behaviour. >> >> One option is to read all the information synchronously and store it in >> a per-cpu area with atomic instructions, then queue the NMI. Another >> option is to have another callback which tells us that the NMI is done, >> and have a busy loop wait until the NMI is delivered. >> >> > Callback seems too heavy, may affect the performance badly. Maybe a short > queue would help, though this one is more complex. > The patch we're replying to adds callbacks (to read rip, etc.), so it's no big deal. For the queue solution, a queue of size one would probably be sufficient even if not guaranteed by the spec. I don't see how the cpu can do another guest entry without delivering the NMI. > But I am still curious if we extend the region, how much it would help. Would > get a result soon... > Yes, interesting to see what the latency is. If it's reasonably short (and I expect it will be so), we can do the busy wait solution. If we have an NMI counter somewhere, we can simply wait until it changes. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/