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Date: Thu, 31 Mar 2022 10:53:44 -0400 From: Phil Auld <pauld@...hat.com> To: Dietmar Eggemann <dietmar.eggemann@....com> Cc: linux-kernel@...r.kernel.org, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, Peter Zijlstra <peterz@...radead.org>, linux-arm-kernel@...ts.infradead.org Subject: Re: [PATCH v2] arch/arm64: Fix topology initialization for core scheduling On Thu, Mar 31, 2022 at 04:37:50PM +0200 Dietmar Eggemann wrote: > On 31/03/2022 15:21, Phil Auld wrote: > > On Thu, Mar 31, 2022 at 11:04:31AM +0200 Dietmar Eggemann wrote: > >> On 30/03/2022 17:56, Phil Auld wrote: > > [...] > > >> Ah, the reason is that smt_mask is not correctly setup, so we bail on > >> `cpumask_weight(smt_mask) == 1` for !leaders in: > >> > >> notify_cpu_starting() > >> cpuhp_invoke_callback_range() > >> sched_cpu_starting() > >> sched_core_cpu_starting() > >> > >> which leads to rq->core not being correctly set for !leader-rq's. > >> > > > > Exactly, sorry I was not clearer. smt_mask must be setup correctly > > by the time sched_core_cpu_starting() is called. (Maybe I should crib > > some of the above lines into the commit message?) > > Yeah, maybe, it wouldn't hurt I guess. IMHO mentioning stress-ng's prctl > needs PR_SCHED_CORE support could also be handy since today's stress-ng > packages don't seem to have this yet. > My scripts clone it so I did not realize that was not in prepackaged versions yet. But that said, that's really just a way to tickle the problem. Anyone using core scheduling on such a system will hit this (at least the WARN part, the actual crash was harder to create w/o all the threads and tasks stress-ng uses). I can send a v3 with a further commit message update. Cheers, Phil --
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