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[209.85.208.175]) by smtp.gmail.com with ESMTPSA id w6sm28137lfn.64.2020.11.19.09.24.03 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Nov 2020 09:24:03 -0800 (PST) Received: by mail-lj1-f175.google.com with SMTP id i17so7111849ljd.3 for ; Thu, 19 Nov 2020 09:24:03 -0800 (PST) X-Received: by 2002:a2e:8e33:: with SMTP id r19mr5946254ljk.102.1605806643076; Thu, 19 Nov 2020 09:24:03 -0800 (PST) MIME-Version: 1.0 References: <20201118194838.753436396@linutronix.de> <20201118204007.269943012@linutronix.de> <20201119093834.GH3306@suse.de> <20201119111411.GL3121378@hirez.programming.kicks-ass.net> In-Reply-To: <20201119111411.GL3121378@hirez.programming.kicks-ass.net> From: Linus Torvalds Date: Thu, 19 Nov 2020 09:23:47 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch V4 4/8] sched: Make migrate_disable/enable() independent of RT To: Peter Zijlstra Cc: Mel Gorman , Thomas Gleixner , LKML , "the arch/x86 maintainers" , Christoph Hellwig , Matthew Wilcox , Daniel Vetter , Andrew Morton , Linux-MM , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Daniel Bristot de Oliveira Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 19, 2020 at 3:14 AM Peter Zijlstra wrote: > > I still hate all of this, and I really fear that with migrate_disable() > available, people will be lazy and usage will increase :/ > > Case at hand is this series, the only reason we need it here is because > per-cpu page-tables are expensive... No, I think you as a scheduler person just need to accept it. Because this is certainly not the only time migration limiting has come up, and no, it has absolutely nothing to do with per-cpu page tables being completely unacceptable. The scheduler people need to get used to this. Really. Because ASMP is just going to be a fact. There are few things more futile than railing against reality, Peter. Honestly, the only argument I've ever heard against limiting migration is the whole "our scheduling theory doesn't cover it". So either throw the broken theory away, or live with it. Theory that doesn't match reality isn't theory, it's religion. Linus