Re: [Xen-devel] Xen 4 TSC problems

[Olivier Hanesse <olivier.hanesse@xxxxxxxxx>]

Mark is running with a E5620 Xeon processor.

I got a L5420.

What is very strange is that this jump is always 50min, not more, not less. And we are not alone with Mark to have this issue.

So it might have an explanation somewhere (bad counter, overflow, bug or somethings).

So maybe this 300 seconds * 10 is a lead. 

Another point, what is the number "warp" really means, in the output of "xm debug-key -s".

Should I monitor this number ?  Maybe I could predict a jump by watching this value ?

2011/2/24 Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>

Just a wild guess, but this in Olivier's posted output:

(XEN) Platform timer appears to have unexpectedly wrapped 10 or more times.

and the fact that a 32-bit HPET wrap is ~300 seconds and, with the
"10 or more times", 10 * 300 seconds is 3000 seconds, might be a clue
(or a complete red herring, but I thought it worth mentioning).

Mark and Olivier, it would be interesting to know if you are
using the same processor/system.

> -----Original Message-----
> From: Keir Fraser [mailto:keir.xen@xxxxxxxxx]
> Sent: Thursday, February 24, 2011 7:52 AM
> To: Olivier Hanesse; Jan Beulich
> Cc: Mark Adams; Jeremy Fitzhardinge; xen-devel@xxxxxxxxxxxxxxxxxxx; Xen
> Users; Dan Magenheimer; Keir Fraser
> Subject: Re: [Xen-devel] Xen 4 TSC problems
>
> 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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