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Re: [Xen-devel] credit accounting question

On 19/6/08 06:03, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

> Then the net effect is in last accounting cycle (30ms), 'B' is put
> in a lower priority compared to other spin vcpus. Not sure whether
> this is an over-sensitive concern in real workload, since above
> is just one assumed scenario in my mind. Maybe in reality above
> transient unfairness will be fixed in a long run, from average P.O.V.
> Simply from design point of view, how much overhead may add
> to schedule phase if adding fine-grained accounting there? The
> accounting logic in csched_vcpu_acct seems simple enough.
> csched_cpu_pick may be still kept in this 10ms tick, or relax it
> to 30ms is also OK?

I'm not really sure that the credit scheduler needs to be tick-based. Why
not account at nanosecond granularity and do away with the arbitrary tick
granularity? Some degree of hysteresis or minimum scheduling granularity
could be used to avoid an unnecessarily high rate of context switches.

 -- Keir

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