Messages in this thread | | | Date | Wed, 14 Mar 2012 16:45:00 +0100 | Subject | Re: [RFC PATCH 14/14] sched: implement usage tracking | From | Vincent Guittot <> |
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On 14 March 2012 16:01, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > 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.
Shouldn't usage_avg_sum and runnable_avg_sum be equal for rq because running and runnable parameters are equals and we have the same computation ?
Furthermore, the geometric series should ensure us that final value shouldn't be larger than 1024/(1-y) which is around 47000 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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