Messages in this thread | | | Date | Wed, 4 Jun 2014 12:55:59 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 08/11] sched: get CPU's activity statistic |
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On Wed, Jun 04, 2014 at 11:36:19AM +0100, Morten Rasmussen wrote: > On Wed, Jun 04, 2014 at 11:17:24AM +0100, Peter Zijlstra wrote: > > Let me explain the 75%, take any one of the above scenarios. Lets call > > the two tasks A and B, and let for a moment assume A always wins and > > runs first, and then B. > > > > So A will be runnable for 25%, B otoh will be runnable the entire time A > > is actually running plus its own running time, giving 50%. Together that > > makes 75%. > > > > If you release the assumption that A runs first, but instead assume they > > equally win the first execution, you get them averaging at 37.5% each, > > which combined will still give 75%. > > But that is assuming that the first task gets to run to completion of it > busy period. If it uses up its sched_slice and we switch to the other > tasks, they both get to wait. > > For example, if the sched_slice is 5 ms and the busy period is 10 ms, > the execution pattern would be: A, B, A, B, idle, ... In that case A is > runnable for 15 ms and B is for 20 ms. Assuming that the overall period > is 40 ms, the A runnable is 37.5% and B is 50%.
Indeed, with preemption added you can pull this out further. You can then indeed get infinitesimally close to 100% with this. [unhandled content-type:application/pgp-signature] | |