From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH v2] KVM: x86: update masterclock values on TSC writes Date: Wed, 5 Nov 2014 16:19:28 -0200 Message-ID: <20141105181928.GA608@amt.cnet> References: <20141104233044.GB29191@amt.cnet> <5459EF85.5010206@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm-devel To: Paolo Bonzini Return-path: Received: from mx1.redhat.com ([209.132.183.28]:51506 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751122AbaKESTs (ORCPT ); Wed, 5 Nov 2014 13:19:48 -0500 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id sA5IJlOZ026428 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Wed, 5 Nov 2014 13:19:48 -0500 Content-Disposition: inline In-Reply-To: <5459EF85.5010206@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Nov 05, 2014 at 10:36:05AM +0100, Paolo Bonzini wrote: > On 05/11/2014 00:30, 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?