Messages in this thread | | | Subject | Re: [PATCH RFC] select_idle_sibling experiments | From | Mike Galbraith <> | Date | Thu, 28 Apr 2016 15:17:46 +0200 |
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On Thu, 2016-04-28 at 14:00 +0200, Peter Zijlstra wrote: > On Wed, Apr 06, 2016 at 09:27:24AM +0200, Mike Galbraith wrote: > > sched: ratelimit nohz > > > > Entering nohz code on every micro-idle is too expensive to bear. > > > > Signed-off-by: Mike Galbraith <efault@gmx.de> > > > +int sched_needs_cpu(int cpu) > > +{ > > +> > > > if (tick_nohz_full_cpu(cpu)) > > +> > > > > > return 0; > > + > > +> > > > return cpu_rq(cpu)->avg_idle < sysctl_sched_migration_cost; > > So the only problem I have with this patch is the choice of limit. This > isn't at all tied to the migration cost.
Yup.
> And some people are already twiddling with the migration_cost knob to > affect the idle_balance() behaviour -- making it much more agressive by > dialing it down. When you do that you also loose the effectiveness of > this proposed usage, even though those same people would probably want > this. > > Failing a spot of inspiration for a runtime limit on this; we might have > to introduce yet another knob :/
I'll roll one with a yet another of it's very own.
-Mike
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