Messages in this thread | | | Subject | Re: [RFC PATCH 14/14] sched: implement usage tracking | From | Peter Zijlstra <> | Date | Wed, 14 Mar 2012 16:01:08 +0100 |
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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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