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RE: [Xen-devel] Time goes backwards in dom0 in xen-unstable

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "Xen-Devel (E-mail)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Time goes backwards in dom0 in xen-unstable
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Wed, 15 Apr 2009 07:31:00 +0800
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Thread-topic: [Xen-devel] Time goes backwards in dom0 in xen-unstable
>From: Dan Magenheimer
>Sent: 2009年4月15日 3:37
>I'm seeing some "Time went backwards" errors reported
>in dom0 in near-tip (c/s 19515) xen-unstable build.
>It's rare and random and not reproducible, but here's
>the report that just showed up.  There was no load
>running at the time.
>I can move to 3.4-rc1 if that would be helpful but I
>don't remember seeing any time-related changes recently.
>This was on my dual-core test machine which reports
>lots of power management info during Xen boot.

could you add "hpetbroadcast" in grub.conf? This is possibly
caused by PIT broadcast again as in your Mcycles thread.
http://markmail.org/thread/uzqcmjuu6uc5xxqd is one
write-up about those side-effects when cpuidle gets enabled
by default in Xen 3.4. Preferred way to do broadcast is always
to use HPET, however by far one missing feature makes PIT
as default broadcast on most platforms. That missing feature
is to emulate RTC interrupt with IRQ8 replaced by HPET if
using legacy replacement mode. We're adding that emulation
now and hopefully get it ready in several days and in final
Xen 3.4 release. At that time, PIT will be only turned to
on some old platform (then no deep C-state support) or weird 
BIOS not exporting HPET (then simply disable cpuidle).


>Timer ISR/0: Time went backwards: delta=-14971734 
>delta_cpu=25028266 shadow=3655
>618577922 off=580668482 processed=3656214217729 
> 0: 3656174217729
> 1: 3656214217729
>Timer ISR/0: Time went backwards: delta=-14971447 
>delta_cpu=25028553 shadow=3655
>618577922 off=590668621 processed=3656224217729 
> 0: 3656184217729
> 1: 3656224217729
>Timer ISR/0: Time went backwards: delta=-14970691 
>delta_cpu=25029309 shadow=3655
>618577922 off=620669383 processed=3656254217729 
> 0: 3656214217729
> 1: 3656254217729
>Timer ISR/0: Time went backwards: delta=-14970623 
>delta_cpu=25029377 shadow=3655
>618577922 off=630669373 processed=3656264217729 
> 0: 3656224217729
> 1: 3656254217729
>Timer ISR/0: Time went backwards: delta=-14969392 
>delta_cpu=25030608 shadow=3655
>618577922 off=680670676 processed=3656314217729 
> 0: 3656274217729
> 1: 3656304217729
>Timer ISR/0: Time went backwards: delta=-14967619 
>delta_cpu=25032381 shadow=3655
>618577922 off=740672580 processed=3656374217729 
> 0: 3656334217729
> 1: 3656374217729
>Timer ISR/0: Time went backwards: delta=-14967315 
>delta_cpu=25032685 shadow=3655
>618577922 off=750672771 processed=3656384217729 
> 0: 3656344217729
> 1: 3656374217729
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