From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 147A6C4363D for ; Thu, 24 Sep 2020 12:44:21 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9985D206D9 for ; Thu, 24 Sep 2020 12:44:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="pYIhFhER" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9985D206D9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=zJE4d6n2HTkiooDjm4GI7Ro6OWj3aw79vN4cRXfktJE=; b=pYIhFhERSUixtgkekG49vBvoe PIuhsvQMj+Vps5DW4/XQM1aBtCnVFuMSq6ZSO4rjBgI1bMpEpYEIergkHOTRZ554d2dD7H9LG9luf wb5lcTRR467OFoxxXdSy1r0LdLKHegTjgAvWg6sQYi6IcygK65FWdWmro8FOYH/wO8p9fVsLitrF4 G++aGEBXaGoLxV40yusbCAAuXTeIVGORzx613aJaFZcbjp8zMoCPDm7cd2WE2GGOGMmDG5xRmbWVx RGVlrX4kvWXzcY7AxOiH1ezQWyIcuo9p5YZYcYlklPrdhPYgnkmo3qPo7jekEGvDLJQFRgHUm7r5W GzCqcd5zA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLQaQ-0005QK-3s; Thu, 24 Sep 2020 12:42:58 +0000 Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLQaG-0005M9-J5; Thu, 24 Sep 2020 12:42:48 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id C0F753007CD; Thu, 24 Sep 2020 14:42:41 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id A98B620297EC5; Thu, 24 Sep 2020 14:42:41 +0200 (CEST) Date: Thu, 24 Sep 2020 14:42:41 +0200 From: Peter Zijlstra To: Steven Rostedt Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends Message-ID: <20200924124241.GK2628@hirez.programming.kicks-ass.net> References: <87a6xjd1dw.fsf@nanos.tec.linutronix.de> <87sgbbaq0y.fsf@nanos.tec.linutronix.de> <20200923084032.GU1362448@hirez.programming.kicks-ass.net> <20200923115251.7cc63a7e@oasis.local.home> <874kno9pr9.fsf@nanos.tec.linutronix.de> <20200923171234.0001402d@oasis.local.home> <871riracgf.fsf@nanos.tec.linutronix.de> <20200924083241.314f2102@gandalf.local.home> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200924083241.314f2102@gandalf.local.home> X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juri Lelli , David Airlie , Benjamin Herrenschmidt , Sebastian Andrzej Siewior , Joonas Lahtinen , dri-devel , linux-mips@vger.kernel.org, Ben Segall , Max Filippov , Guo Ren , linux-sparc , Vincent Chen , Will Deacon , Ard Biesheuvel , linux-arch , Vincent Guittot , Herbert Xu , Michael Ellerman , the arch/x86 maintainers , Russell King , linux-csky@vger.kernel.org, Mel Gorman , "open list:SYNOPSYS ARC ARCHITECTURE" , linux-xtensa@linux-xtensa.org, Paul McKenney , intel-gfx , linuxppc-dev , Jani Nikula , Greentime Hu , Rodrigo Vivi , Thomas Gleixner , Dietmar Eggemann , Linux ARM , Chris Zankel , Michal Simek , Thomas Bogendoerfer , Nick Hu , Linux-MM , Linus Torvalds , LKML , Arnd Bergmann , Daniel Vetter , Vineet Gupta , Paul Mackerras , Andrew Morton , Daniel Bristot de Oliveira , "David S. Miller" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Sep 24, 2020 at 08:32:41AM -0400, Steven Rostedt wrote: > Anyway, instead of blocking. What about having a counter of number of > migrate disabled tasks per cpu, and when taking a migrate_disable(), and there's > already another task with migrate_disabled() set, and the current task has > an affinity greater than 1, it tries to migrate to another CPU? That doesn't solve the problem. On wakeup we should already prefer an idle CPU over one running a (RT) task, but you can always wake more tasks than there's CPUs around and you'll _have_ to stack at some point. The trick is how to unstack them correctly. We need to detect when a migrate_disable() task _should_ start running again, and migrate away whoever is in the way at that point. It turns out, that getting selected for pull-balance is exactly that condition, and clearly a migrate_disable() task cannot be pulled, but we can use that signal to try and pull away the running task that's in the way. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel