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SubjectRe: [PATCH v3 2/7] sched: accumulate per-cfs_rq cpu usage
* Nikhil Rao <ncrao@google.com> [2010-10-13 07:41:46]:

> On Wed, Oct 13, 2010 at 6:59 AM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> > * Nikhil Rao <ncrao@google.com> [2010-10-13 06:46:18]:
> >
> >> > Quick question for cfs_b->quota == RUNTIME_INF, won't cfs_b->runtime
> >> > be always > 0?
> >>
> >> Hi Balbir,
> >>
> >> cfs_b->runtime can be 0 if the task group exhausts its quota.
> >> cfs_b->runtime is a counter that is periodically refreshed to
> >> cfs_b->quota, and is decremented every time a cfs_rq requests a slice.
> >>
> >
> > Thanks, Nikhil
> >
> > I saw several checks for quota == RUNTIME_INF and saw updates not
> > happening. Do we track usage for cgroups with infinite quota? IOW, is
> > runtime updated? If so, why?
> >
>
> We don't track usage or update runtime for cgroups with infinite
> quota. Most of these RUNTIME_INF checks are usually at the top of the
> functions and return immediately. The checks in the middle of
> functions are mostly to prevent races when cfs_b->quota is updated.
>
> And ... I think I might have misunderstood your original question. Let
> me try answering that again. We check for quota == RUNTIME_INF (in
> addition to cfs_b->runtime > 0) because it is possible that the global
> pool is updated to RUNTIME_INF between the quota check in
> account_cfs_rq_quota() and when the actual quota is distributed in
> tg_request_cfs_quota(). I hope that answers your original question.
>

Yes, it does, thanks!

--
Three Cheers,
Balbir


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