From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH v2] KVM: x86: update masterclock values on TSC writes Date: Wed, 05 Nov 2014 20:47:29 +0100 Message-ID: <545A7ED1.3050504@redhat.com> References: <20141104233044.GB29191@amt.cnet> <5459EF85.5010206@redhat.com> <20141105181928.GA608@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: kvm-devel To: Marcelo Tosatti Return-path: Received: from mail-wg0-f49.google.com ([74.125.82.49]:33790 "EHLO mail-wg0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751513AbaKETrd (ORCPT ); Wed, 5 Nov 2014 14:47:33 -0500 Received: by mail-wg0-f49.google.com with SMTP id x13so1746933wgg.22 for ; Wed, 05 Nov 2014 11:47:32 -0800 (PST) In-Reply-To: <20141105181928.GA608@amt.cnet> Sender: kvm-owner@vger.kernel.org List-ID: On 05/11/2014 19:19, Marcelo Tosatti wrote: >>> > > + * If the vcpus have matched TSCs and host clocksource is TSC, >>> > > + * perform request to enable masterclock. >>> > > + * >>> > > + * If the masterclock is enabled, perform request to update >>> > > + * masterclock values. >>> > > + */ >>> > > + if ((vcpus_matched && gtod->clock.vclock_mode == VCLOCK_TSC) || >>> > > + ka->use_master_clock) >> > >> > This is not an explanation, it is a literal translation from C to >> > English. :) Can you also explain the why, especially for the first half >> > of the condition? >> > >> > Paolo > The comment on top of pvclock_update_vm_gtod_copy says: > > "Rely on synchronization of host TSCs and guest TSCs for monotonicity." > > Then with this patch > > "If the vcpus have matched TSCs and host clocksource is TSC" > > Is it sufficient to add > > "Masterclock requires synchronized guest TSC and host clocksource TSC" > to this patch? Got it now, thanks. I think I misread one "enable" as "update" in your comment, sorry. I'll apply v2 tomorrow. Paolo