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=-7.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 B326EC4332B for ; Sat, 16 Jan 2021 17:09:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8BC192310F for ; Sat, 16 Jan 2021 17:09:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726984AbhAPRGP (ORCPT ); Sat, 16 Jan 2021 12:06:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:56974 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727062AbhAPQkG (ORCPT ); Sat, 16 Jan 2021 11:40:06 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9E82C2087E; Sat, 16 Jan 2021 15:45:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1610811942; bh=OfveYr4oEYaNENOH4nieZPzwuRhlzFLXdVKngXxsswA=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=joRSRbKMQ09t+ffLEzOmbIY3Qzso3VzokwwNBzG+vImVlCqMW3MgIEZcWxPP1ScOl LfCHoErA88cQAL9P6UGKFLMsgElyLJ6qPofCUFGjv7iWB+Q7yzvXtZtwBLiRhThjRI 7oDyJwM8PD5IPJpuhvjAlsRHz/nnT9WPLNSspWu0rdlG56V0lm1f/uLUKh6iHktDPq oXtFWpoSEY2NenrtfIRWhDZjQTtU7aLjqJvOaUt9vSkzQBU+B9fIKRP0YDjFhqFeDG +MiOJLbxvSsgGDfdlew+4iK+tYA0GX1wYQEudOFLHAnjCGpK4H5BtvIUOc6tCEpdqf J/z8ZKiVLODPA== Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 6F4DA35225DC; Sat, 16 Jan 2021 07:45:42 -0800 (PST) Date: Sat, 16 Jan 2021 07:45:42 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: mingo@kernel.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, jiangshanlai@gmail.com, valentin.schneider@arm.com, cai@redhat.com, vincent.donnefort@arm.com, decui@microsoft.com, vincent.guittot@linaro.org, rostedt@goodmis.org, tj@kernel.org Subject: Re: [PATCH 0/8] sched: Fix hot-unplug regressions Message-ID: <20210116154542.GQ2743@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20210116113033.608340773@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 16, 2021 at 04:25:58PM +0100, Peter Zijlstra wrote: > On Sat, Jan 16, 2021 at 12:30:33PM +0100, Peter Zijlstra wrote: > > Hi, > > > > These patches (no longer 4), seems to fix all the hotplug regressions as per > > nearly a 100 18*SRCU-P runs over-night. > > > > I did clean up the patches, so possibly I wrecked it again. I've started new > > runs and will again leave them running over-night. > > Hurph... I've got one splat from this version, one I've not seen before: > > [ 68.712848] Dying CPU not properly vacated! > ... > [ 68.744448] CPU1 enqueued tasks (2 total): > [ 68.745018] pid: 14, name: rcu_preempt > [ 68.745557] pid: 18, name: migration/1 > > Paul, rcu_preempt, is from rcu_spawn_gp_kthread(), right? Afaict that > doesn't even have affinity.. /me wonders HTH that ended up on the > runqueue so late. Yes, rcu_preempt is from rcu_spawn_gp_kthread(), and you are right that the kernel code does not bind it anywhere. If this is rcutorture, there isn't enough of a userspace to do the binding there, eihter. Wakeups for the rcu_preempt task can happen in odd places, though. Grasping at straws... Would Frederic's series help? This is in -rcu here: cfd941c rcu/nocb: Detect unsafe checks for offloaded rdp 028d407 rcu: Remove superfluous rdp fetch 38e216a rcu: Pull deferred rcuog wake up to rcu_eqs_enter() callers 53775fd rcu/nocb: Perform deferred wake up before last idle's need_resched() check 1fbabce rcu/nocb: Trigger self-IPI on late deferred wake up before user resume 2856844 entry: Explicitly flush pending rcuog wakeup before last rescheduling points 4d959df sched: Report local wake up on resched blind zone within idle loop 2617331 entry: Report local wake up on resched blind zone while resuming to user 79acd12 timer: Report ignored local enqueue in nohz mode I have been including these in all of my tests of your patches. Thanx, Paul