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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8A76EECAAD3 for ; Wed, 14 Sep 2022 11:04:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 07C6F8D0002; Wed, 14 Sep 2022 07:04:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 02B5F6B0078; Wed, 14 Sep 2022 07:04:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E34EF8D0002; Wed, 14 Sep 2022 07:04:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id D08766B0075 for ; Wed, 14 Sep 2022 07:04:33 -0400 (EDT) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id A6FB5C096D for ; Wed, 14 Sep 2022 11:04:33 +0000 (UTC) X-FDA: 79910407626.30.4687F6C Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf06.hostedemail.com (Postfix) with ESMTP id F2D6C180092 for ; Wed, 14 Sep 2022 11:04:32 +0000 (UTC) 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 ams.source.kernel.org (Postfix) with ESMTPS id 0C782B81A40; Wed, 14 Sep 2022 11:04:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 244FBC433D6; Wed, 14 Sep 2022 11:04:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1663153469; bh=tbx0ApNcuaaHnoKpUSFbEFs9vNYZFNnjuUmTNGNSz84=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=N6tuKtMG5Wmi2TiNPlqXNBlsCCM7q7I4weRyHU3u7SOpc+dpRiZWg/K4KmkjzcpRg BCMAtkSNyStcTOmwtbpvDianxv2Te0aJjOemrRB3hCdd5piRmtOFvbr39TdCoxmphd ytgetmLNAQ80hgq5GRNAjPy8rNeidiEdPsXEZVUeTR9PChFvfVrSyoU6rek9ZHflYe JRQElf5dlxjXAHMTwF23DENQRw0hZTJTLAFn0Fxl1f3Cz8vFLYj0QnvlCVo4yhhLOF U1hR0bUvrYkCgWQVZRJS7LMX7oNnAlwEacKl0afM8jxz4mvhIpomZoTNh+0c1ua5w4 7PZKF9/UM9V8g== Date: Wed, 14 Sep 2022 13:04:26 +0200 From: Frederic Weisbecker To: Aaron Tomlin Cc: Marcelo Tosatti , cl@linux.com, tglx@linutronix.de, mingo@kernel.org, peterz@infradead.org, pauld@redhat.com, neelx@redhat.com, oleksandr@natalenko.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v7 2/3] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too Message-ID: <20220914110426.GD1936@lothringen> References: <20220817191346.287594886@redhat.com> <20220817191524.201253713@redhat.com> <20220909121224.GA220905@lothringen> <20220912143822.irn6xhs2etmumqlt@ava.usersys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220912143822.irn6xhs2etmumqlt@ava.usersys.com> ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=N6tuKtMG; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf06.hostedemail.com: domain of frederic@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=frederic@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1663153473; a=rsa-sha256; cv=none; b=rvIQNA8JhS1C9bZuZS3L3mG+v2dVMKcmGCem9ChX6cxesQk2ZlFxavynUquIuAvbjRQKoK gzZNH9JN5ZBh6JCD+SGlEWbElK61ohAgKDaTjQmnItSNN0LBNzTWMDcyv6yMSvH3W40mm1 hb881wb5/ofuLvCs/srb8e7TLsWXBrA= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1663153473; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=rIvGa/ne9GI+aBflWlmdjgspBugCC4z+0uA3g4VHJrs=; b=Szc7M1vvWErstpwq0+7cJyN19nBC5w0RUZXQn/Jqn239t65dcP4ruAOu2T79UgThDvyXv3 DI0eDLThj51Wm4013yZQUbqjO9HN72CQ+TEXJDCUc7LSHIVfeoICaGe2A+ca7HB3ylDuHp xZ+73sVEnppiATt5Wx2z+90dPxSs9S4= X-Rspam-User: Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=N6tuKtMG; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf06.hostedemail.com: domain of frederic@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=frederic@kernel.org X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: F2D6C180092 X-Stat-Signature: 3gfupp3usw9wyadmsazg3of3rf36rttj X-HE-Tag: 1663153472-631877 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Sep 12, 2022 at 03:38:23PM +0100, Aaron Tomlin wrote: > On Fri 2022-09-09 16:35 -0300, Marcelo Tosatti wrote: > Hi Frederic, > > Sorry about that. How about the following: > > - Note: CPU X is part of 'tick_nohz_full_mask' > > 1. CPU Y migrated running task A to CPU X that > was in an idle state i.e. waiting for an IRQ; > marked the current task on CPU X to need/or > require a reschedule i.e., set TIF_NEED_RESCHED > and invoked a reschedule IPI to CPU X > (see sched_move_task()) > > 2. CPU X acknowledged the reschedule IPI. Generic > idle loop code noticed the TIF_NEED_RESCHED flag > against the idle task and attempts to exit of the > loop and calls the main scheduler function i.e. > __schedule(). > > Since the idle tick was previously stopped no > scheduling-clock tick would occur. > So, no deferred timers would be handled > > 3. Post transition to kernel execution Task A > running on CPU X, indirectly released a few pages > (e.g. see __free_one_page()); CPU X's > 'vm_stat_diff[NR_FREE_PAGES]' was updated and zone > specific 'vm_stat[]' update was deferred as per the > CPU-specific stat threshold > > 4. Task A does invoke exit(2) and the kernel does > remove the task from the run-queue; the idle task > was selected to execute next since there are no > other runnable tasks assigned to the given CPU > (see pick_next_task() and pick_next_task_idle()) > > 5. On return to the idle loop since the idle tick > was already stopped and can remain so (see [1] > below) e.g. no pending soft IRQs, no attempt is > made to zero and fold CPU X's vmstat counters > since reprogramming of the scheduling-clock tick > is not required/or needed (see [2]) Much better thanks. Please cut the patch in two patches: one that fixes the stuff in the idle path and another one that fixes the return to user path. The first one is definetly a fix, the second one is rather a feature that is definetly wanted as well but I need to think it through further. > > > > Kind regards, > > -- > Aaron Tomlin >