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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F3C2ACDB47E for ; Wed, 18 Oct 2023 18:13:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344720AbjJRSNV (ORCPT ); Wed, 18 Oct 2023 14:13:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34766 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231307AbjJRSNU (ORCPT ); Wed, 18 Oct 2023 14:13:20 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8BC1B98 for ; Wed, 18 Oct 2023 11:13:18 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1DD34C433C8; Wed, 18 Oct 2023 18:13:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1697652798; bh=/5tzr5CWv4KijS8Ooc9na1PJM05K7T5Kk3SSmP4w6vY=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=IIOasrIMBAbX4CLhg3deTsjXR8yFA57r50gAu3R5/kvkGPRzlzn9DMwSDj3iURR+a vSqOFSSSTvFpRTpXV3EONc3rdGtS34LCP+vrBnl9hm2AD0m2QKVhAZoGryetUK36No esin8l5jYx5nmlCUeqRRN09SgVcmDuUOc5qEseq1oNUDFW8Y5SXE3vyA1qaJcd5GWB Fnjrhho+zTPWt/9BoO2d1dUe0oQ8VLx1iGOGHYRwuqHa9/OpeeJK6QBACIvWPb4pFe 1TbFfbMmPjhlk7aA0pAi6sZRVtNM8nZSkQZIUwRPEgg11QkRz/FbHT9zit1FiWxaOM B17p3keRBw8GQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id A3B86CE0DE3; Wed, 18 Oct 2023 11:13:17 -0700 (PDT) Date: Wed, 18 Oct 2023 11:13:17 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Thomas Gleixner , Linus Torvalds , Peter Zijlstra , Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com, Frederic Weisbecker , Daniel Bristot de Oliveira Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED Message-ID: <98f9ff35-5d71-4706-afe1-7e039afbcaaf@paulmck-laptop> Reply-To: paulmck@kernel.org References: <87ttrngmq0.ffs@tglx> <87jzshhexi.ffs@tglx> <87pm1c3wbn.ffs@tglx> <20231018103146.4856caa8@gandalf.local.home> <20231018140035.107f5177@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231018140035.107f5177@gandalf.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 18, 2023 at 02:00:35PM -0400, Steven Rostedt wrote: > On Wed, 18 Oct 2023 10:55:02 -0700 > "Paul E. McKenney" wrote: > > > > If everything becomes PREEMPT_RCU, then the above should be able to be > > > turned into just: > > > > > > if (!disable_irq) > > > local_irq_disable(); > > > > > > rcu_momentary_dyntick_idle(); > > > > > > if (!disable_irq) > > > local_irq_enable(); > > > > > > And no cond_resched() is needed. > > > > Even given that CONFIG_PREEMPT_RCU=n still exists, the fact that > > run_osnoise() is running in kthread context with preemption and everything > > else enabled (am I right?), then the change you suggest should work fine. > > There's a user space option that lets you run that loop with preemption and/or > interrupts disabled. Ah, thank you. Then as long as this function is not expecting an RCU reader to span that call to rcu_momentary_dyntick_idle(), all is well. This is a kthread, so there cannot be something else expecting an RCU reader to span that call. > > > > Again. There is no non-preemtible RCU with this model, unless I'm > > > > missing something important here. > > > > > > Daniel? > > > > But very happy to defer to Daniel. ;-) > > But Daniel could also correct me ;-) If he figures out a way that it is broken, he gets to fix it. ;-) Thanx, Paul