From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zachary Amsden Subject: Re: Clock jumps Date: Thu, 27 May 2010 12:22:29 -1000 Message-ID: <4BFEF0A5.8040301@redhat.com> References: <20100525062100.GP22163@redhat.com> <4BFD5616.6070302@cora.nwra.com> <4D7E210A-4694-4B6E-B721-6024CE96ABC0@suse.de> <4BFEE9F3.8040200@redhat.com> <4BFEEE3A.1010403@birkenwald.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: Bernhard Schmidt Return-path: In-Reply-To: <4BFEEE3A.1010403@birkenwald.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 05/27/2010 12:12 PM, Bernhard Schmidt wrote: > On 27.05.2010 23:53, Zachary Amsden wrote: > > Hello Zachary, > >> I have server side fixes for this kvm-clock which seem to give me a >> stable clock on this machine, but for true SMP stability, you will need >> Glauber's guest side changes to kvmclock as well. It is impossible to >> guarantee strictly monotonic clocksource across multiple CPUs when >> frequency is dynamically changing (and also because of the C1E idle >> problems). > > Is all this relevant only when the host is on TSC? Because I have seen > these jumps when the host was on HPET and the guests were using > kvm-clock. It doesn't matter what the host uses (although the host on TSC with unstable TSC can make things worse), tsc and kvmclock sources in the guest will be unstable regardless.