| Subject | Re: [RFC PATCH 00/14] sched: entity load-tracking re-work | From | Peter Zijlstra <> | Date | Tue, 13 Mar 2012 18:28:31 +0100 |
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On Mon, 2012-03-12 at 10:39 +0000, Morten Rasmussen wrote: > I have looked at traces of both runnable time and usage time trying to > understand why you use runnable time as your load metric and not usage > time which seems more intuitive. What I see is that runnable time > depends on the total runqueue load. If you have many tasks on the > runqueue they will wait longer and therefore have higher individual > load_avg_contrib than they would if the were scheduled across more CPUs. > Usage time is also affected by the number of tasks on the runqueue as > more tasks means less CPU time. However, less usage can also just mean > that the task does not execute very often. This would make a load > contribution estimate based on usage time less accurate. Is this your > reason for choosing runnable time?
Exactly so, you cannot ever have more than 100% usage, so no matter how many tasks you stick on a cpu, you'll never get over that 100% and thus this is not a usable load metric.
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