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Date: Tue, 14 Apr 2020 17:35:07 -0400 From: Vineeth Remanan Pillai <vpillai@...italocean.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Nishanth Aravamudan <naravamudan@...italocean.com>, Julien Desfossez <jdesfossez@...italocean.com>, Tim Chen <tim.c.chen@...ux.intel.com>, Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Paul Turner <pjt@...gle.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Linux List Kernel Mailing <linux-kernel@...r.kernel.org>, Frédéric Weisbecker <fweisbec@...il.com>, Kees Cook <keescook@...omium.org>, Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.com>, Aaron Lu <aaron.lwe@...il.com>, Aubrey Li <aubrey.intel@...il.com>, "Li, Aubrey" <aubrey.li@...ux.intel.com>, Valentin Schneider <valentin.schneider@....com>, Mel Gorman <mgorman@...hsingularity.net>, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Paolo Bonzini <pbonzini@...hat.com>, Joel Fernandes <joelaf@...gle.com>, Joel Fernandes <joel@...lfernandes.org> Subject: Re: [RFC PATCH 03/13] sched: Core-wide rq->lock > Aside from the fact that it's probably much saner to write this as: > > rq->core_enabled = static_key_enabled(&__sched_core_enabled); > > I'm fairly sure I didn't write this part. And while I do somewhat see > the point of disabling core scheduling for a core that has only a single > thread on, I wonder why we care. > I think this change was to fix some crashes which happened due to uninitialized rq->core if a sibling was offline during boot and is onlined after coresched was enabled. https://lwn.net/ml/linux-kernel/20190424111913.1386-1-vpillai@digitalocean.com/ I tried to fix it by initializing coresched members during a cpu online and tearing it down on a cpu offline. This was back in v3 and do not remember the exact details. I shall revisit this and see if there is a better way to fix the race condition above. Thanks, Vineeth
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