Re: [accounting regression since rc1] scheduler updates

Ingo Molnar
2007-08-20T19:12:50Z

* Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:

> > If a virtual CPU is idle then i think the "real = steal, virtual =
> > 0" way of thinking about idle looks a bit unnatural to me - wouldnt
> > it be better to think in terms of "steal = 0, virtual = real" ?
> > Basically a virtual CPU can idle at "perfect speed", without the
> > host "stealing" any cycles from it. And with that way of thinking,
> > if s390 passed in the real-idle-time value to the new callbacks
> > below it would all fall into place. Hm?
>
> How you think about an idle cpu depends on your viewpoint. The source
> for the virtual cpu time on s390 is the cpu timer. This timer is
> stopped when a virtual cpu looses the physical cpu, so it seems
> natural to me to think that real=steal, virtual=0 because the cpu
> timer is stopped while the cpu is idle. The other way of thinking
> about it is as valid though.

my thinking is this: the structure of "idle time" only matters if it can
be observed from "within" a virtual machine - via timers. Are on s390
any of the typical app-visible timers (timer_list, etc.) driven by the
virtual tick? [which slows down if a virtual CPU is scheduled away by
the host/monitor/hypervisor?] Or is the virtual tick only affecting
scheduling/cpu-accounting statistics in essence?

Ingo