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RE: [Xen-devel] s_time going backwards on same processor?

To: <dan.magenheimer@xxxxxxxxxx>, "Xen-Devel (E-mail)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] s_time going backwards on same processor?
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Wed, 23 Jul 2008 14:16:19 +0800
Cc: Dave Winchell <dwinchell@xxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] s_time going backwards on same processor?
>From: Dan Magenheimer
>Sent: 2008年7月23日 5:59
>
>Are there any conditions/events in a running Xen system
>that can cause two consecutive calls to get_s_time()
>*on the same processor* to return values such that
>the second one is smaller than the first (other than
>64-bit wraparound)?  I ask because I'm fairly sure
>that I observed this, and Xen system time on the
>same processor moved backwards about 40us (40000ns).

Weird. Did you observe same phenomenon by putting
your test code in any code path, or just on some specific
point?

Does clocksource matters?

Did you enable any cpufreq or cpuidle feature?

Only observed on SMP Xen?

Thanks,
Kevin

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