From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754087AbYJBLwq (ORCPT ); Thu, 2 Oct 2008 07:52:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753249AbYJBLwi (ORCPT ); Thu, 2 Oct 2008 07:52:38 -0400 Received: from mx2.redhat.com ([66.187.237.31]:46983 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753227AbYJBLwh (ORCPT ); Thu, 2 Oct 2008 07:52:37 -0400 Message-ID: <48E4B5E8.60400@redhat.com> Date: Thu, 02 Oct 2008 14:52:08 +0300 From: Avi Kivity User-Agent: Thunderbird 2.0.0.16 (X11/20080723) MIME-Version: 1.0 To: Zachary Amsden CC: Gerd Hoffmann , Alok Kataria , Ingo Molnar , "H. Peter Anvin" , Thomas Gleixner , LKML , the arch/x86 maintainers , Jeremy Fitzhardinge , Rusty Russell , Daniel Hecht , "Jun.Nakajima@Intel.Com" Subject: Re: Use CPUID to communicate with the hypervisor. References: <1222472815.29886.43.camel@alok-dev1> <48E090B6.2080809@redhat.com> <1222710924.30247.21.camel@alok-dev1> <48E1227B.9040809@redhat.com> <1222717085.30247.44.camel@alok-dev1> <48E15AC7.2080603@redhat.com> <1222734838.30247.102.camel@alok-dev1> <48E1DF2C.9050409@redhat.com> <1222792958.7330.16.camel@bodhitayantram.eng.vmware.com> In-Reply-To: <1222792958.7330.16.camel@bodhitayantram.eng.vmware.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 Zachary Amsden wrote: >> Well, that should be clearly defined, that is my point. When asking the >> hypervisor for the tsc instead of running a calibration loop, then we >> have a small bit of paravirtualization: The guest is aware that it runs >> on a hypervisor and just asks it directly. So while we are at it we can >> also define a way to communicate tsc freq changes between host and >> guest, so the cost of trap'n'emulate tsc reads can be avoided. Or we >> define "tsc is constant" and leave it to the hypervisor to make sure it >> > > For our purposes, we define TSC is constant. > I believe VMware doesn't actually change cpu frequency dynamically. But what about hypervisors that do? and what about large machines, which do not actually have a constant tsc? You are defining something as constant which in fact is not constant. -- error compiling committee.c: too many arguments to function