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 09601C4741F for ; Wed, 23 Sep 2020 15:54:52 +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 ABCBA235F7 for ; Wed, 23 Sep 2020 15:54:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="P6BQ1oTq" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org ABCBA235F7 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-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: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=ycG6SNc9ajmkWZ5IxBAh20yb5KOaRlpR6P9i2otiU7I=; b=P6BQ1oTq+Cw1uWs48oBMy1QgW rundaPdkya6dIfs/sCbvguRtW+6Ol52D3+D6VXsz2Ul5+fnYEp0qOKAd/Y7NM6POXhdXiGOyMelet Una8KIZ13CBsJ7rIbIkv9W7Gq8WZpzHMI98+LS6MvJMyjUHPzkpwMs4G8huLcnGVIkzMV+FIXiD9G Xp4GZmWVmF3AiTqzDaN/ux+VI1I5BzN99SgbKSnFSnz/GcHcRU0I01liklCLQgnpTKND4FEnMNokr vUmk3Tee0NiEREDmd0YsO7q6x7ki++NO+opg+8jfDa6sggxRkykwbH/ezn3E6HjJe6E1i3/JjneZI L0AADdW4w==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kL74v-0007Cd-7h; Wed, 23 Sep 2020 15:53:09 +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 1kL74r-0007Aq-TE; Wed, 23 Sep 2020 15:53:07 +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 492262223E; Wed, 23 Sep 2020 15:52:54 +0000 (UTC) Date: Wed, 23 Sep 2020 11:52:51 -0400 From: Steven Rostedt To: peterz@infradead.org Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends Message-ID: <20200923115251.7cc63a7e@oasis.local.home> In-Reply-To: <20200923084032.GU1362448@hirez.programming.kicks-ass.net> References: <20200919091751.011116649@linutronix.de> <87mu1lc5mp.fsf@nanos.tec.linutronix.de> <87k0wode9a.fsf@nanos.tec.linutronix.de> <87eemwcpnq.fsf@nanos.tec.linutronix.de> <87a6xjd1dw.fsf@nanos.tec.linutronix.de> <87sgbbaq0y.fsf@nanos.tec.linutronix.de> <20200923084032.GU1362448@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-20200923_115306_079404_E5372779 X-CRM114-Status: GOOD ( 17.37 ) 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 Wed, 23 Sep 2020 10:40:32 +0200 peterz@infradead.org wrote: > However, with migrate_disable() we can have each task preempted in a > migrate_disable() region, worse we can stack them all on the _same_ CPU > (super ridiculous odds, sure). And then we end up only able to run one > task, with the rest of the CPUs picking their nose. What if we just made migrate_disable() a local_lock() available for !RT? I mean make it a priority inheritance PER CPU lock. That is, no two tasks could do a migrate_disable() on the same CPU? If one task does a migrate_disable() and then gets preempted and the preempting task does a migrate_disable() on the same CPU, it will block and wait for the first task to do a migrate_enable(). No two tasks on the same CPU could enter the migrate_disable() section simultaneously, just like no two tasks could enter a preempt_disable() section. In essence, we just allow local_lock() to be used for both RT and !RT. Perhaps make migrate_disable() an anonymous local_lock()? This should lower the SHC in theory, if you can't have stacked migrate disables on the same CPU. -- Steve _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel