From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [RFC PATCH v2 2/2] add support for Hyper-V invariant TSC Date: Thu, 23 May 2013 18:14:41 +0300 Message-ID: <20130523151441.GH26157@redhat.com> References: <1368947197-9033-1-git-send-email-vrozenfe@redhat.com> <1368947197-9033-3-git-send-email-vrozenfe@redhat.com> <20130522005046.GA7589@amt.cnet> <643480794.5761686.1369207375451.JavaMail.root@redhat.com> <20130522212330.GA29387@amt.cnet> <519DB4CF.8050003@dlhnet.de> <20130523091316.GJ4725@redhat.com> <20130523133559.GA14454@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Peter Lieven , Vadim Rozenfeld , kvm@vger.kernel.org, pl@dlh.net To: Marcelo Tosatti Return-path: Received: from mx1.redhat.com ([209.132.183.28]:40229 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758447Ab3EWPOv (ORCPT ); Thu, 23 May 2013 11:14:51 -0400 Content-Disposition: inline In-Reply-To: <20130523133559.GA14454@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On Thu, May 23, 2013 at 10:35:59AM -0300, Marcelo Tosatti wrote: > On Thu, May 23, 2013 at 12:13:16PM +0300, Gleb Natapov wrote: > > > > > > > >"Reference TSC during Save and Restore and Migration > > > > > > > >To address migration scenarios to physical platforms that do not support > > > >iTSC, the TscSequence field is used. In the event that a guest partition > > > >is migrated from an iTSC capable host to a non-iTSC capable host, the > > > >hypervisor sets TscSequence to the special value of 0xFFFFFFFF, which > > > >directs the guest operating system to fall back to a different clock > > > >source (for example, the virtual PM timer)." > > > > > > > >Why it would not/does not work after migration? > > > > > > > > > > > > > > what exactly do we heed the reference TSC for? the reference counter alone works great and it seems > > > that there is a lot of trouble and crash possibilities involved with the referece tsc. > > > > > Reference TSC is even faster. There should be no crashed with proper > > implementation. > > > > -- > > Gleb. > > Lack of invariant TSC support in the host. Proper implementation will disable reference TSC in this case. -- Gleb.