Messages in this thread | | | From | Uladzislau Rezki <> | Date | Thu, 30 Nov 2017 13:30:42 +0100 | Subject | Re: [PATCH RFC 1/2] sched: Minimize the idle cpu selection race window. |
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On Wed, Nov 29, 2017 at 07:15:21PM +0100, Mike Galbraith wrote: > On Wed, 2017-11-29 at 11:41 +0100, Uladzislau Rezki wrote: > > 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.
> > Which means nothing to an LB operation in progress. > <snip> static void nohz_idle_balance(...) ... /* * If this cpu gets work to do, stop the load balancing * work being done for other cpus. Next load * balancing owner will pick it up. */ if (need_resched()) break; ... <snip>
> > But whatever, I'm not going to argue endlessly about something I think > should be blatantly obvious. IMO, this is a couple points shy of > pointless. That's my 'C' to this RFC in a nutshell. I'm done. > Thank you.
Vlad
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