From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jan Kiszka <jan.kiszka@web.de>
Subject: Re: [PATCH] fix kvmclock bug
Date: Fri, 24 Sep 2010 09:28:09 +0200
Message-ID: <4C9C5309.5080403@web.de>
References: <4C95560D.3050108@redhat.com>
Mime-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
 protocol="application/pgp-signature";
 boundary="------------enig82CA5094B0405D4C18042561"
Cc: Marcelo Tosatti <mtosatti@redhat.com>, Avi Kivity <avi@redhat.com>,
	kvm <kvm@vger.kernel.org>, Glauber Costa <glommer@redhat.com>
To: Zachary Amsden <zamsden@redhat.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from fmmailgate03.web.de ([217.72.192.234]:58566 "EHLO
	fmmailgate03.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754776Ab0IXH20 (ORCPT <rfc822;kvm@vger.kernel.org>);
	Fri, 24 Sep 2010 03:28:26 -0400
In-Reply-To: <4C95560D.3050108@redhat.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

This is an OpenPGP/MIME signed message (RFC 2440 and 3156)
--------------enig82CA5094B0405D4C18042561
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable

Am 19.09.2010 02:15, Zachary Amsden wrote:
> For CPUs with unstable TSC, we null time offset between not just VCPU
> switches, but all preemptions of the kvm thread.  This makes a bug much=

> more likely where the kvmclock values are updated before a successful
> exit from virt, causing an underflow.
>=20
> The null offsetting was added at : bf0fb4a42ba7eb362f4013bd2e9320966679=
3e66
> The underflow happens with this additional patch :=20
> cf839f5da2b0779b9ec8b990f851fb4e7d681da0
>=20
> There is a secondary bug, which is that TSC fails to advance with real
> time on unstable TSC, but the fix is much more involved (it requires th=
e
> TSC catchup code).
>=20
> For now, this patch is sufficient to get things working again for me.

=2E..but not for me. I still face stuck (or infinitely slow) guests that
want to use kvmclock once tsc_unstable gets set. Or is this patch
addressing a different issue?

Jan


--------------enig82CA5094B0405D4C18042561
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename="signature.asc"

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.15 (GNU/Linux)
Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org/

iEYEARECAAYFAkycUwkACgkQitSsb3rl5xTgSACg1dkp/5Yd8vGl+WnEYBxoICdp
qpEAmwWBuYfNr+g0BXKc5Lf58cRvh8Wp
=SVz5
-----END PGP SIGNATURE-----

--------------enig82CA5094B0405D4C18042561--