Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 10 Oct 2014 09:17:22 +0200 | Subject | Re: [PATCH v7 6/7] sched: replace capacity_factor by usage |
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On 9 October 2014 17:18, Peter Zijlstra <peterz@infradead.org> wrote: > On Thu, Oct 09, 2014 at 04:18:02PM +0200, Vincent Guittot wrote: >> On 9 October 2014 14:16, Peter Zijlstra <peterz@infradead.org> wrote: >> > On Tue, Oct 07, 2014 at 02:13:36PM +0200, Vincent Guittot wrote: >> >> +static inline bool >> >> +group_has_capacity(struct lb_env *env, struct sg_lb_stats *sgs) >> >> { >> >> + if ((sgs->group_capacity * 100) > >> >> + (sgs->group_usage * env->sd->imbalance_pct)) >> >> + return true; >> > >> > Why the imb_pct there? We're looking for 100% utilization, not 130 or >> > whatnot, right? >> >> Having exactly 100% is quite difficult because of various rounding. >> So i have added a margin/threshold to prevent any excessive change of the state. >> I have just to use the same margin/threshold than in other place in >> load balance. >> > > Yet you failed to mention this anywhere. Also does it really matter?
yes i think it latter because it give a more stable view of the "overload state" and "have free capacity state" of the CPU. One additional point is that the imbalance_pct will ensure that a cpu/group will not been seen as having capacity if its available capacity is only 1-5% which will generate spurious task migration
I will add these details in the commit log and in a comment in the code
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