On Tue, Nov 28, 2017 at 11:49:11AM +0100, Mike Galbraith wrote: > On Tue, 2017-11-28 at 10:34 +0100, Uladzislau Rezki wrote: > > On Fri, Nov 24, 2017 at 07:46:30PM +0100, Mike Galbraith wrote: > > > > > My view is you're barking up the wrong tree: you're making the idle > > > data SIS is using more accurate, but I question the benefit. That it > > > makes an imperfect placement decision occasionally due to raciness is > > > nearly meaningless compared to the cost of frequent bounce. > > > Before sitting down and start testing, i just illustrated how we can > > apply claim_wake_up to ilb asking community a specific view on it: > > drawbacks, pros/cons, proposals etc. > > Even if you make the thing atomic, what is ILB supposed to do, look > over its shoulder every step of the way and sh*t it's pants if somebody > touches claim_wake_up as it's about to or just after it did something? If nohz.idle_cpus_mask is set for particular CPU together with claim mask, it means that TIF_NEED_RESCHED is coming or is already in place. When a CPU hits idle_thread a claim bit gets reset and proceed to no_hz mode unless it runs into scheduler_ipi or so.
> > If you intend to make all of LB race free, good luck. > > -Mike Vlad
