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Date: Wed, 29 Nov 2017 11:41:47 +0100 From: Uladzislau Rezki <urezki@...il.com> To: Mike Galbraith <efault@....de> Cc: Uladzislau Rezki <urezki@...il.com>, Atish Patra <atish.patra@...cle.com>, Peter Zijlstra <peterz@...radead.org>, Joel Fernandes <joelaf@...gle.com>, LKML <linux-kernel@...r.kernel.org>, Brendan Jackman <brendan.jackman@....com>, Josef Bacik <jbacik@...com>, Ingo Molnar <mingo@...hat.com> Subject: Re: [PATCH RFC 1/2] sched: Minimize the idle cpu selection race window. 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
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