From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: swiotlb=force in Konrad's xen-pcifront-0.8.2 pvops domU kernel with PCI passthrough Date: Thu, 18 Nov 2010 12:54:59 -0500 Message-ID: <20101118175459.GA4245@Krystal> References: <20101112165541.GA10339@dumpdata.com> <20101112223333.GD26189@dumpdata.com> <20101116185748.GA11549@dumpdata.com> <20101116201349.GA18315@dumpdata.com> <20101118171936.GA29275@dumpdata.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20101118171936.GA29275@dumpdata.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Konrad Rzeszutek Wilk Cc: Jeremy Fitzhardinge , Xen-devel , andrew.thomas@oracle.com, keir.fraser@eu.citrix.com, chris.mason@oracle.com, Dante Cinco List-Id: xen-devel@lists.xenproject.org * Konrad Rzeszutek Wilk (konrad.wilk@oracle.com) wrote: > Keir, Dan, Mathieu, Chris, Mukesh, [...] > Doubt it. Your best bet to figure this out is to play with ftrace, or > perf trace. But I don't know how well they work with Xen nowadays - Jeremy > and Mathieu Desnoyers poked it a bit and I think I overheard that Mathieu got > it working? I did port LTTng to the Xen hypervisor in a past life, but I did not have time to maintain this port in parallel with the Linux kernel LTTng. So I doubt these bits would be very useful today, as a new port would be needed for compatibility with newer lttng tools. If you can afford to use older Xen hypervisors with older Linux kernels and old LTTng/LTTV versions, then you could gather a synchronized trace across the hypervisor/Dom0/DomUs, but it would require some work for recent Xen versions. Currently, we've been focusing our efforts on tracing of KVM, which works very well. We support analysis of traces taken from different host/guest domains, as long as the TSCs are synchronized. So an option here would be to deploy LTTng on both your dom0 and domU kernels, gather traces of both in parallel while you run your workload, and compare the resulting traces (load both dom0 and domU traces into one trace set within lttv). Comparing the I/O behavior with a bare-metal trace should give a good insight into what's different. At least you'll be able to follow the path taken by each I/O request, except for what's happening in Xen, which will be a black box. Thanks, Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com