Re: [PATCH 2/11] Sched clock paravirt op

From: Zachary Amsden
Date: Tue Feb 06 2007 - 18:51:44 EST


Jeremy Fitzhardinge wrote:
Zachary Amsden wrote:
Jeremy Fitzhardinge wrote:
Zachary Amsden wrote:
Scheduled (or available) time and real time are good notions. Stolen
time is debatable. But TSC is basically just always wrong. That's
why I don't want to overload the rdtsc operation.
Well, in the Xen case it is actually guaranteed to be correct and useful
as real time, but that's definitely not something we can expect in
general. But you're talking specifically about schedulable vcpu time
here, right?
Not schedulable time, scheduled time (schedulable - scheduled) = stolen

I meant "schedulable" (perhaps "usable" would be better) from the
guest's perspective: total amount of real cpu time each vcpu gets. ie:
(real - schedulable) = stolen. So I think we're talking about the same
thing.

Yes, I think so. The point though, is the for Xen, TSC is real time. So it won't do for the scheduler, which must be schedulable time.

Zach

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