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=-6.5 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,USER_AGENT_SANE_2 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 2CC89C2D0E2 for ; Thu, 24 Sep 2020 13:51:58 +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 96BD6206CD for ; Thu, 24 Sep 2020 13:51:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="htu5P3Ic" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 96BD6206CD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-snps-arc-bounces+linux-snps-arc=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:MIME-Version:References:In-Reply-To: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=j6caIxFum0OzTjIg5z9ohjaPenKDHXvRZpxWdRVbvV8=; b=htu5P3IcpPmUuYcbOQyWfNSV4 gw6AY/hnwYvbZDdCqxtRqqQZ5T5ZOUGX1bcG5oifAskd6UpGG5YImjV2yetoVL8oDS+nea7Mt5zz3 N8rO8MgLkGCuOptnLJ18CP+7X1ZY2PIErXyUuL/05ZV7hGZCp0VLZvYcPQTM8Yo4Yb/Na9MALazOe NXwFFhezs1qc1sia0dQtJLg6UvCjtA0s4z9XFgi0Un8gg60U0Q67jxTIYEnBJQVwFrL8yU1H5m3bF yJQKBBijRdCTcew5qP4p/TAzF2T9CjsS1z6zp+AeN9FeTC1/Ua53Im16YpV7UJY8LIuigzLBltkvk JRzIjVA4A==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLRfA-0000yJ-H9; Thu, 24 Sep 2020 13:51:56 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kLRez-0000tB-KA; Thu, 24 Sep 2020 13:51:47 +0000 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C7B5D206CD; Thu, 24 Sep 2020 13:51:39 +0000 (UTC) Date: Thu, 24 Sep 2020 09:51:38 -0400 From: Steven Rostedt To: Peter Zijlstra Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends Message-ID: <20200924095138.5318d242@oasis.local.home> In-Reply-To: <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> <20200924124241.GK2628@hirez.programming.kicks-ass.net> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200924_095145_821524_5F941B70 X-CRM114-Status: GOOD ( 23.43 ) X-BeenThere: linux-snps-arc@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on Synopsys ARC Processors 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-snps-arc" Errors-To: linux-snps-arc-bounces+linux-snps-arc=archiver.kernel.org@lists.infradead.org On Thu, 24 Sep 2020 14:42:41 +0200 Peter Zijlstra wrote: > 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. Yes, understood. > > 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. Unless of course that running task is in a migrate disable section itself ;-) But I guess we will always have that SHC, and there will always be a scenario that you can't balance properly. But hopefully in practice we wont see that. How to handle kmap_local(), will migrate_disable() be used only for 32bit or, for consistency, will it also apply to 64bit? -- Steve _______________________________________________ linux-snps-arc mailing list linux-snps-arc@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-snps-arc