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Re: [Xen-devel] [PATCH 1/2] cpu steal time accounting

On 22 Feb 2006, at 14:27, Rik van Riel wrote:

Is accounting user/system time an unnecessary extra? I guess we already
do it by sampling at tick granularity anyway?

Should 'steal time' include blocked time when the guest had no work to

No, this is idle time.  If the guest had no work to do,
it wasn't suffering from contention of the CPU.

But the 'vcpu_time' you read out of Xen excludes time spent blocked/unrunnable. Won't you end up accounting that as it it were involuntary preemption? Also: 1. What if a guest gets preempted for lots of short time periods (less than a jiffy). Then some arbitrary time in the future is preempted for long enough to activate you stolen-time logic. Won't you end up incorrectly accounting the accumulated short time periods? 2. Is the Xen provided 'vcpu_time', divided down into jiffies, even comparable with the kstats that you sum? What about accumulated rounding errors in 'vcpu_time' and the kstats causing relative drift between them over time?

 -- Keir

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