From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.xen@gmail.com>
Subject: Re: [Xen-devel] Xen 4 TSC problems
Date: Thu, 24 Feb 2011 14:52:03 +0000
Message-ID: <C98C2113.13CA9%keir.xen@gmail.com>
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To: Olivier Hanesse <olivier.hanesse@gmail.com>, Jan Beulich <JBeulich@novell.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>, xen-devel@lists.xensource.com, Keir Fraser <keir@xen.org>, Dan Magenheimer <dan.magenheimer@oracle.com>, Xen Users <xen-users@lists.xensource.com>, Mark Adams <mark@campbell-lange.net>
List-Id: xen-devel@lists.xenproject.org

On 24/02/2011 14:20, "Olivier Hanesse" <olivier.hanesse@gmail.com> wrote:

> Both dom0 and domUs are affected by this" jump".
>=20
> I expect to see something like "TSC marked as reliable, warp =3D 0".=A0
> I got this on newer hardware with same config/distros.

It depends on the CPU itself, older CPUs do not have the super-stable TSC
features. But that should never cause a massive 3000s time jump.

> Is there a way to measure if it is a TSC warp ? to point out a cpu tsc is=
sue ?

The TSC warps or out-of-sync issues that we could reasonably expect would b=
e
on the order of microseconds. A 3000s warp is something else entirely. Xen
is very confused and/or some TSC or platform timer has jumped a long way
(indicating a hardware/firmware issue).

 -- Keir

>=20
> 2011/2/24 Jan Beulich <JBeulich@novell.com>
>>>>> On 24.02.11 at 12:57, Olivier Hanesse <olivier.hanesse@gmail.com> wro=
te:
>>> I tried to turn off cstates with max_cstate=3D0 without success (still "n=
ot
>>> reliable").
>>>=20
>>> With cpuidle=3D0, I also got :
>>>=20
>>> (XEN) TSC has constant rate, deep Cstates possible, so not reliable,
>>> warp=3D3022 (count=3D1)
>>=20
>> This message by itself isn't telling much I believe.
>>=20
>>> xm info | grep command
>>> xen_commandline =A0 =A0 =A0 =A0: dom0_mem=3D512M cpuidle=3D0 loglvl=3Dall guest_loglv=
l=3Dall
>>> dom0_max_vcpus=3D1 dom0_vcpus_pin console=3Dvga,com1 com1=3D19200,8n1
>>>=20
>>> Keir :
>>>=20
>>> Using clocksource=3Dpit :
>>>=20
>>> (XEN) Platform timer is 1.193MHz PIT
>>>=20
>>> I also got :
>>>=20
>>> (XEN) TSC has constant rate, deep Cstates possible, so not reliable,
>>> warp=3D3262 (count=3D2)
>>=20
>> The question is whether any of this eliminates the time jumps seen
>> by your DomU-s (from your past mails I wasn't actually sure whether
>> Dom0 also experienced this problem, albeit it would be odd if it didn't)=
.
>>=20
>> Jan
>>=20
>> Jan
>>=20
>=20
>=20