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    SubjectRe: [RFC PATCH 14/14] sched: implement usage tracking
    On Tue, 2012-03-13 at 17:57 +0100, Vincent Guittot wrote:
    > > struct sched_avg {
    > > u64 runnable_avg_sum, runnable_avg_period;
    > > u64 last_runnable_update, decay_count;
    > > + u32 usage_avg_sum;
    > Why usage_avg_sum is 32bits whereas runnable_avg_sum and
    > runnable_avg_period are 64bits long ? You are doing the same
    > computation on these 3 variables. Only the computation need to be done
    > in 64bits but the result could be saved in 32bits ?

    Since you can never use more than 100% of cpu time, usage_avg_sum is
    bound to 100% of the period, which (assuming your period < ~4s) should
    thus still fit in the ~4s u32 provides.

    Runnable otoh is not bound by that and thus we cannot guarantee the
    value stays within the ~4s value range.

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