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Date: Wed, 15 Jun 2016 20:03:19 +0100 From: Dietmar Eggemann <dietmar.eggemann@....com> To: Mike Galbraith <umgwanakikbuti@...il.com>, Peter Zijlstra <peterz@...radead.org> Cc: Yuyang Du <yuyang.du@...el.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [rfc patch] sched/fair: Use instantaneous load for fork/exec balancing On 15/06/16 17:03, Mike Galbraith wrote: > On Wed, 2016-06-15 at 16:32 +0100, Dietmar Eggemann wrote: > >>> In general, the fuzz helps us to not be so spastic. I'm not sure that >>> we really really need to care all that much, because I strongly suspect >>> that it's only gonna make any difference at all in corner cases, but >>> there are real world cases that matter. I know for fact that schbench >>> (facebook) which is at least based on a real world load fails early due >>> to us stacking tasks due to that fuzzy view of reality. In that case, >>> it's because the fuzz consists of a high amplitude aging sawtooth.. >> >> ... only for fork/exec? > > No. Identical workers had longish work/sleep cycle, aging resulted in > weights that ranged from roughly 300-700(ish), depending on when you > peeked at them. > > -Mike > Isn't there a theoretical problem with the scale_load() on CONFIG_64BIT machines on tip/sched/core? load.weight has a higher resolution than runnable_load_avg (and so the values in the rq->cpu_load[] array). Theoretically because [forkexec|wake]_idx is 0 so [target|source]_load() is nothing else than weighted_cpuload().
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