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Date: Wed, 25 Nov 2020 14:45:37 +0100 From: Peter Zijlstra <peterz@...radead.org> To: "Joel Fernandes (Google)" <joel@...lfernandes.org> Cc: Nishanth Aravamudan <naravamudan@...italocean.com>, Julien Desfossez <jdesfossez@...italocean.com>, Tim Chen <tim.c.chen@...ux.intel.com>, Vineeth Pillai <viremana@...ux.microsoft.com>, Aaron Lu <aaron.lwe@...il.com>, Aubrey Li <aubrey.intel@...il.com>, tglx@...utronix.de, linux-kernel@...r.kernel.org, mingo@...nel.org, torvalds@...ux-foundation.org, fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com, Phil Auld <pauld@...hat.com>, Valentin Schneider <valentin.schneider@....com>, Mel Gorman <mgorman@...hsingularity.net>, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Paolo Bonzini <pbonzini@...hat.com>, vineeth@...byteword.org, Chen Yu <yu.c.chen@...el.com>, Christian Brauner <christian.brauner@...ntu.com>, Agata Gruza <agata.gruza@...el.com>, Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>, graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com, pjt@...gle.com, rostedt@...dmis.org, derkling@...gle.com, benbjiang@...cent.com, Alexandre Chartre <alexandre.chartre@...cle.com>, James.Bottomley@...senpartnership.com, OWeisse@...ch.edu, Dhaval Giani <dhaval.giani@...cle.com>, Junaid Shahid <junaids@...gle.com>, jsbarnes@...gle.com, chris.hyser@...cle.com, Ben Segall <bsegall@...gle.com>, Josh Don <joshdon@...gle.com>, Hao Luo <haoluo@...gle.com>, Tom Lendacky <thomas.lendacky@....com>, Aubrey Li <aubrey.li@...ux.intel.com>, "Paul E. McKenney" <paulmck@...nel.org>, Tim Chen <tim.c.chen@...el.com> Subject: Re: [PATCH -tip 31/32] sched: Add a coresched command line option On Tue, Nov 17, 2020 at 06:20:01PM -0500, Joel Fernandes (Google) wrote: > Some hardware such as certain AMD variants don't have cross-HT MDS/L1TF > issues. Detect this and don't enable core scheduling as it can > needlessly slow those device down. > > However, some users may want core scheduling even if the hardware is > secure. To support them, add a coresched= option which defaults to > 'secure' and can be overridden to 'on' if the user wants to enable > coresched even if the HW is not vulnerable. 'off' would disable > core scheduling in any case. This is all sorts of wrong, and the reason is because you hard-coded that stupid policy. Core scheduling should always be available on SMT (provided you did that CONFIG_ thing). Even on AMD systems RT tasks might want to claim the core exclusively.
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