From mboxrd@z Thu Jan  1 00:00:00 1970
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Subject: Re: KVM-Clock
Date: Wed, 24 Feb 2016 13:20:17 +0100
Message-ID: <20160224122016.GA17209@potion.redhat.com>
References: <B84047ECBD981D4B93EAE5A6245AA361995B00@lhreml501-mbb>
 <B84047ECBD981D4B93EAE5A6245AA361995B16@lhreml501-mbb>
 <20160222200815.GA3189@potion.brq.redhat.com>
 <B84047ECBD981D4B93EAE5A6245AA361995D20@lhreml501-mbb>
 <20160223175130.GA3164@potion.brq.redhat.com>
 <B84047ECBD981D4B93EAE5A6245AA361996018@lhreml501-mbb>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>
To: Avi Cohen <avi.cohen@huawei.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:35427 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1753599AbcBXMUU (ORCPT <rfc822;kvm@vger.kernel.org>);
	Wed, 24 Feb 2016 07:20:20 -0500
Content-Disposition: inline
In-Reply-To: <B84047ECBD981D4B93EAE5A6245AA361996018@lhreml501-mbb>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

2016-02-24 10:32+0000, Avi Cohen:
>> Look at last paragraph of my previous email.
>> (That one has 1 ns accuracy if KVM is using the masterclock.)
> 
> How to make KVM using the masterclock ? - I don't see any masterclock in traces

KVM should use masterclock whenever it can.  Host dmesg can contain
warning about unstable TSC if masterclock is not being used for good
reasons (grep for "TSC unstable" and "unstable TSC").

Relevant tracepoints are (from arch/x86/kvm/trace.h)
  kvm:kvm_update_master_clock
  kvm:kvm_track_tsc
  kvm:kvm_pvclock_update
  kvm:write_tsc_offset

The host is using TSC clocksource, TSC wasn't marked as unstable, guest
didn't screw with MSR_IA32_TSC or MSR_IA32_TSC_ADJUST, and masterclock
still isn't used?