From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752106Ab1AGLXy (ORCPT ); Fri, 7 Jan 2011 06:23:54 -0500 Received: from mx1.redhat.com ([209.132.183.28]:21124 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751970Ab1AGLXw (ORCPT ); Fri, 7 Jan 2011 06:23:52 -0500 Date: Fri, 7 Jan 2011 08:48:59 -0200 From: Marcelo Tosatti To: Zachary Amsden Cc: kvm@vger.kernel.org, Avi Kivity , Glauber Costa , linux-kernel@vger.kernel.org Subject: Re: [KVM TSC trapping / migration 2/2] Add TSC KHZ MSR Message-ID: <20110107104859.GA12056@amt.cnet> References: <1294308645-31113-1-git-send-email-zamsden@redhat.com> <1294308645-31113-3-git-send-email-zamsden@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1294308645-31113-3-git-send-email-zamsden@redhat.com> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 06, 2011 at 12:10:45AM -1000, Zachary Amsden wrote: > Use an MSR to allow "soft" migration to hosts which do not support > TSC trapping. Rather than make this a required element of any > migration protocol, we allow the TSC rate to be exported as a data > field (useful in its own right), but we also allow a one time write > of the MSR during VM creation. The result is that for the common > use case, no protocol change is required to communicate TSC rate > to the receiving host. Migration to hosts which do not support the feature can be achieved by saving/restoring the TSC rate + flags in a subsection. A subsection seems more appropriate than an MSR for this. > This allows administrative tools to configure migration policy > as they see appropriate. Rather than dictate this policy with the > KVM implementation, we properly allow migration to hosts which both > do and do not support setting of the TSC rate on the receiving end. > If it is wished to not support migration to a host which lacks > support for the TSC rate feature, that can be coordinated externally. > > Signed-off-by: Zachary Amsden