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[Xen-users] Re: [Xen-devel] Xen 4 TSC problems

To: Olivier Hanesse <olivier.hanesse@xxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: [Xen-users] Re: [Xen-devel] Xen 4 TSC problems
From: Keir Fraser <keir.xen@xxxxxxxxx>
Date: Thu, 24 Feb 2011 14:52:03 +0000
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir@xxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Xen Users <xen-users@xxxxxxxxxxxxxxxxxxx>, Mark Adams <mark@xxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] Xen 4 TSC problems
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On 24/02/2011 14:20, "Olivier Hanesse" <olivier.hanesse@xxxxxxxxx> wrote:

> Both dom0 and domUs are affected by this" jump".
> I expect to see something like "TSC marked as reliable, warp = 0". 
> 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 issue ?

The TSC warps or out-of-sync issues that we could reasonably expect would be
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

> 2011/2/24 Jan Beulich <JBeulich@xxxxxxxxxx>
>>>>> On 24.02.11 at 12:57, Olivier Hanesse <olivier.hanesse@xxxxxxxxx> wrote:
>>> I tried to turn off cstates with max_cstate=0 without success (still "not
>>> reliable").
>>> With cpuidle=0, I also got :
>>> (XEN) TSC has constant rate, deep Cstates possible, so not reliable,
>>> warp=3022 (count=1)
>> This message by itself isn't telling much I believe.
>>> xm info | grep command
>>> xen_commandline        : dom0_mem=512M cpuidle=0 loglvl=all guest_loglvl=all
>>> dom0_max_vcpus=1 dom0_vcpus_pin console=vga,com1 com1=19200,8n1
>>> Keir :
>>> Using clocksource=pit :
>>> (XEN) Platform timer is 1.193MHz PIT
>>> I also got :
>>> (XEN) TSC has constant rate, deep Cstates possible, so not reliable,
>>> warp=3262 (count=2)
>> 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).
>> Jan
>> Jan

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