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 4CDE3C433F5 for ; Fri, 8 Apr 2022 15:58:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237786AbiDHQAs (ORCPT ); Fri, 8 Apr 2022 12:00:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38344 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231631AbiDHQAm (ORCPT ); Fri, 8 Apr 2022 12:00:42 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ECEF6AE6A; Fri, 8 Apr 2022 08:58:37 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 428C6CE2A4D; Fri, 8 Apr 2022 15:58:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 98943C385A1; Fri, 8 Apr 2022 15:58:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1649433514; bh=0w7CX4PrjpdyKdIGRRbs32uv6uKXSuvOdR768kCHqEc=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=hofeAabyDR6ibecdIuTeVv4ItV78H+h3JySoIZU/YELvkfkhJsWqckY9RabMpVXRh FbOqk2qW6ggGrXszDGlIavBvL2hI5CpappCPwb8dVLBc7ZXhFVmHmRY0zvpYWt9ftL FncN++P7beuG4N3bSPS52bIbDrIDVoxchA54f10HreJpRTHBP2JN7nRzyRMFsd7lBV 0QwGDlj0/SQUkTBT+KhQR5MeHpvl9xCQRgQl369iN6Fra//GU8e+Rl4bBxXe1Gn+Ww WA/VcHDOcyhkapwuf5IiWgFRoejxUo8iv9uHKL+XzcMjWBHGl2yl0o3qjMeocmRa12 8oS6lWbUVxz2A== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 34DAB5C0176; Fri, 8 Apr 2022 08:58:34 -0700 (PDT) Date: Fri, 8 Apr 2022 08:58:34 -0700 From: "Paul E. McKenney" To: Steven Rostedt Cc: Joel Fernandes , Kalesh Singh , Suren Baghdasaryan , kernel-team , Tejun Heo , Tim Murray , Wei Wang , Kyle Lin , Chunwei Lu , Lulu Wang , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Mathieu Desnoyers , Lai Jiangshan , rcu , LKML Subject: Re: [PATCH v2] EXP rcu: Move expedited grace period (GP) work to RT kthread_worker Message-ID: <20220408155834.GI4285@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220408045734.1158817-1-kaleshsingh@google.com> <20220408113946.056c083e@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220408113946.056c083e@gandalf.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 08, 2022 at 11:39:46AM -0400, Steven Rostedt wrote: > On Fri, 8 Apr 2022 06:21:03 -0400 > Joel Fernandes wrote: > > > > + default !PREEMPT_RT && NR_CPUS <= 32 > > > > What is the benefit of turning it off on PREEMPT_RT, even if > > PREEMPT_RT does not use expedited GPs much post-boot? I would think in > > the future if PREEMPT_RT ever uses expedited GPs, they would want this > > feature even more. I'd rather be future-proof now as I don't see any > > advantages of disabling it on !PREEMPT_RT (And a drawback that the fix > > won't apply to those systems). Also will keep the config simple. > > The default kthread priority is 1. This should not affect PREEMPT_RT, as > PREEMPT_RT users are usually more concerned by the performance of their > higher priority tasks. Priority 1 is not considered an issue. > > I do not see why PREEMPT_RT is special here. Why was it singled out? Because I didn't see the point of doing kthread_create_worker() to create a pair of kthread_worker structuress that were never going to be used in PREEMPT_RT kernels. Or are PREEMPT_RT kernels no longer booting with rcupdate.rcu_normal? Last I knew, they all did this to avoid IPI latencies from expedited grace periods. Has this changed? Thanx, Paul