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 15:45:10 -0700 Message-ID: <47266276.4030000@goop.org> References: <11936994092607-git-send-email-gcosta@redhat.com> <1193697734.9793.86.camel@bodhitayantram.eng.vmware.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: 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: Zachary Amsden Return-path: In-Reply-To: <1193697734.9793.86.camel-cxY/u30q8FloTgUnLF1by8fTvwmfpRNyZeezCHUQhQ4@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 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. > > Also, please cc all the paravirt developers on things related to > paravirt, especially things with such broad effect. I think 400 is a > good value for a perfect native clocksource. >400 should be reserved > for super-real (i.e. paravirt) sources that should always be chosen over > a hardware realistic implementation in a virtual environment. > Yes, agreed. The tsc is never the right thing to use if there's a paravirt clocksource available. What's wrong with rating it 300? What inferior clocksource does it lose out to? Shouldn't that clocksource be lowered? (Why don't we just use 1 to 10?) 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/