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    SubjectRe: [CFS Bandwidth Control v4 5/7] sched: add exports tracking cfs bandwidth control statistics
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    On Thu, 2011-02-24 at 19:26 -0800, Paul Turner wrote:
    > On Wed, Feb 23, 2011 at 5:32 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
    > > On Tue, 2011-02-15 at 19:18 -0800, Paul Turner wrote:
    > >> + raw_spin_lock(&cfs_b->lock);
    > >> + cfs_b->throttled_time += (rq->clock - cfs_rq->throttled_timestamp);
    > >> + raw_spin_unlock(&cfs_b->lock);
    > >
    > > That seems to put the cost of things on the wrong side. Read is rare,
    > > update is frequent, and you made the frequent thing the most expensive
    > > one.
    >
    > Hum.. the trade-off here is non-trivial I think
    >
    > - This update is only once per-quota period (*if* we throttled within
    > that period). This places the frequency in the 10s-100s of ms range.
    > - Sampling would probably occur on an order of once a second (assuming
    > some enterprise management system that cares about these statistics).

    Ugh,. people are really polling state like that? If the event is rare
    pushing state is much saner.


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