From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [PATCH] raise tsc clocksource rating Date: Mon, 29 Oct 2007 15:52:33 -0700 Message-ID: <47266431.1010500@goop.org> References: <11936994092607-git-send-email-gcosta@redhat.com> <1193697734.9793.86.camel@bodhitayantram.eng.vmware.com> <20071029224852.GA27547@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Zachary Amsden , avi-i/T1Zxg06OZWk0Htik3J/w@public.gmane.org, kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, Dan Hecht , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Glauber de Oliveira Costa , Glauber de Oliveira Costa , --cc-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, Garrett Smith To: Ingo Molnar Return-path: In-Reply-To: <20071029224852.GA27547-X9Un+BFzKDI@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Ingo Molnar wrote: > * Zachary Amsden wrote: > > >> On Mon, 2007-10-29 at 20:10 -0300, Glauber de Oliveira Costa wrote: >> >>> From: Glauber de Oliveira Costa >>> >>> tsc is very good time source (when it does not have drifts, does not >>> change it's frequency, i.e. when it works), so it should have its rating >>> raised to a value greater than, or equal 400. >>> >>> Since it's being a tendency among paravirt clocksources to use values >>> around 400, we should declare tsc as even better: So we use 500. >>> >> Why is the TSC better than a paravirt clocksource? In our case this >> is definitely inaccurate. Paravirt clocksources should be preferred >> to TSC, and both must be made available in hardware for platforms >> which do not support paravirt. >> > > if it's inaccurate why are you exposing it to the guest then? Native > only uses the TSC if it's safe and accurate to do so. > It is used as part of the Xen clocksource as a short term extrapolator, with correction parameters supplied by the hypervisor. It should never be used directly. J ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/