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=-2.6 required=3.0 tests=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 196AFC433DF for ; Sun, 17 May 2020 16:20:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E138920809 for ; Sun, 17 May 2020 16:20:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589732406; bh=TDO7xsmcKGjAPbJRGrjHQpoxl4fnbpgAAlG8ud6evxA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=vi8uubwKGtUBQfURIlMZ1cVT3MZEP50G9vPTv96RcuPoXS8d4TVQwBi221LtfJv5/ /19p7SxnOaWLnDympgJ6WHdU7Dxz9/LVRj9K9t+UKiYje9Dn9SPtSu/oIqHCkzdNU6 TLJOP263urrmV5TXxxTOuHaC1R2oZBsH8sJv6ATc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728070AbgEQQUF (ORCPT ); Sun, 17 May 2020 12:20:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:34428 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728010AbgEQQUF (ORCPT ); Sun, 17 May 2020 12:20:05 -0400 Received: from localhost (lfbn-ncy-1-985-231.w90-101.abo.wanadoo.fr [90.101.63.231]) (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 95D2A2070A; Sun, 17 May 2020 16:20:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589732405; bh=TDO7xsmcKGjAPbJRGrjHQpoxl4fnbpgAAlG8ud6evxA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dLNpaudrp6xh0pygeVR9AKioUlPIP6uUjvX5YnPtFkIqNNkPeMf4UKqjLpueLqpSF l/dMs5M3Lcn5N7NXgGw6fnPzN9SeuTMij3B6SVXauzr0nGcZUi7eYL0EybgunetcXv w8N6P2iuOOd3H4HIMYs2aR7el2fhOtix3swR6gwU= Date: Sun, 17 May 2020 18:20:02 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: Ingo Molnar , Thomas Gleixner , LKML , Peter Zijlstra , Matt Fleming , stable@kernel.org Subject: Re: [PATCH] tick/nohz: Narrow down noise while setting current task's tick dependency Message-ID: <20200517162001.GA30646@lenoir> References: <20200515003429.4317-1-frederic@kernel.org> <20200516030718.GL2869@paulmck-ThinkPad-P72> <20200517133115.GA28573@lenoir> <20200517155322.GQ2869@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200517155322.GQ2869@paulmck-ThinkPad-P72> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, May 17, 2020 at 08:53:22AM -0700, Paul E. McKenney wrote: > On Sun, May 17, 2020 at 03:31:16PM +0200, Frederic Weisbecker wrote: > > On Fri, May 15, 2020 at 08:07:18PM -0700, Paul E. McKenney wrote: > > > On Fri, May 15, 2020 at 02:34:29AM +0200, Frederic Weisbecker wrote: > > > > So far setting a tick dependency on any task, including current, used to > > > > trigger an IPI to all CPUs. That's of course suboptimal but it wasn't > > > > an issue as long as it was only used by posix-cpu-timers on nohz_full, > > > > a combo that nobody seemed to use in real life. > > > > > > > > But RCU started to use task tick dependency on current task to fix > > > > stall issues on callbacks processing. These trigger regular and > > > > undesired system wide IPIs on nohz_full. > > > > > > > > The fix is very easy while setting a tick dependency on the current > > > > task, only its CPU needs an IPI. > > > > > > This passes moderate rcutorture testing. If you want me to take it, please > > > let me know, and otherwise: > > > > > > Tested-by: Paul E. McKenney > > > > If you already have a pending urgent queue, I'd love you to take it. > > If not I can take it. > > Nothing urgent yet in -rcu, so if you would like it in the next merge > window, please take it through your normal upstream path. Got it, thanks!