From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zachary Amsden Subject: Re: KVM timekeeping and TSC virtualization Date: Tue, 24 Aug 2010 18:04:57 -1000 Message-ID: <4C749669.9050204@redhat.com> References: <1282291669-25709-1-git-send-email-zamsden@redhat.com> <20100824221301.GA12173@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Avi Kivity To: Marcelo Tosatti Return-path: Received: from mx1.redhat.com ([209.132.183.28]:16584 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750699Ab0HYEFA (ORCPT ); Wed, 25 Aug 2010 00:05:00 -0400 Received: from int-mx01.intmail.prod.int.phx2.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o7P450xt004451 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Wed, 25 Aug 2010 00:05:00 -0400 In-Reply-To: <20100824221301.GA12173@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On 08/24/2010 12:13 PM, Marcelo Tosatti wrote: > On Thu, Aug 19, 2010 at 10:07:14PM -1000, Zachary Amsden wrote: > >> This patch set implements full TSC virtualization, with both >> trapping and passthrough modes, and intelligent mode switching. >> As a result, TSC will never go backwards, we are stable against >> guest re-calibration attempts, VM reset, and migration. For guests >> which require it, the TSC khz can even be preserved on migration >> to a new host. >> >> The TSC will never be trapped on UP systems unless the host TSC >> actually runs faster than the guest; other conditions, including >> bad hardware and changing speeds are accomodated by using catchup >> mode to keep the guest passthrough TSC in line with the host clock. >> >> What is still needed on top of this is a way to force TSC >> trapping, or disable it entirely, for benchmarking purposes. >> I refrained from adding that last bit because it wasn't clear >> whether the best thing to do is a global 'force TSC trapping' / >> 'force TSC passthrough' / 'intelligent choice', or if this control >> should be on a per-VM level, via an ioctl(), module parameter, >> or sysfs. >> >> John and Thomas I have cc'd on this because it may be relevant to >> their interests and I always appreciate feedback, especially on >> a change set as large and complex as this. >> >> Enjoy. This time, there are no howler monkeys. I've included >> all the feedback I got from previous rounds of this and more. >> > Applied 1-19, thanks. > > Great, thanks. I'll wait for more feedback on the rest and rebase.