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 AD37FE95A91 for ; Mon, 9 Oct 2023 11:26:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346294AbjJIL02 (ORCPT ); Mon, 9 Oct 2023 07:26:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45196 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346291AbjJILZs (ORCPT ); Mon, 9 Oct 2023 07:25:48 -0400 Received: from mail-wm1-x32e.google.com (mail-wm1-x32e.google.com [IPv6:2a00:1450:4864:20::32e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C04ADD5A for ; Mon, 9 Oct 2023 04:25:28 -0700 (PDT) Received: by mail-wm1-x32e.google.com with SMTP id 5b1f17b1804b1-40684f53d11so44151765e9.1 for ; Mon, 09 Oct 2023 04:25:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1696850727; x=1697455527; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:sender:from:to:cc:subject:date:message-id :reply-to; bh=wBNpO06xDlLtemDkhIFD5UcIdTdCSdjnqaYsWe9vtps=; b=V9In6ZTJ4YaXCgX2Zyi8UxnM8E3JIURn5WfzsdbSSJ6XyDu6eC8iOWK9ZOAbCY4tKy /rJURhtdY4+HDrQDbCWEPA0d7at2CJJAhZdpnruWV6+P0Gt1WmuX0VaGzfSavVLJluA0 jRza+3KMOcoQyCCUJGAVaOHaR57T+Rkhb56hu1YiOK9zTY/EXztElOYntuj7ZK5lCpvA vCt/jHOHJ+B01rLiG+tEuGPZmZJM3UdeY15LKloUKr2OCEBjitcXIr1xQwpSAaInJ2OF GcaVIDL/wOpdODnFQFfk4GsuzgoqN6X5noFbzqvDC48q/c2pEkxpRT/REiz0DH7/SwXe dPMg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1696850727; x=1697455527; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:sender:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=wBNpO06xDlLtemDkhIFD5UcIdTdCSdjnqaYsWe9vtps=; b=pqUBd6q1j61g9C8J8kA/PdoQZpELegKrm+Wj434CYmVup3K7rnM1tmBaUrdq+IjbX+ 9rTbJP6Eso44KhYP5BOjkLhLkkCdIMP/PS6CobolYWnTmggnjbJfKVc6AI4Ccw9aVf+w RGvScYh7C1Ell3Tdn8+dOttTaE9nybvFAR2dnF53+HkCtgdKYcGOBWh3fV5P9zodmhI8 Z9n54i4W/b3MHJxJhz/R6D9sHPSanBXJU4xqwnC7tHtZVVTx1WiHRdBKcdAIOKMKeIO/ nlbV3TweSyT0oIEPV9G/rUX20vU1S1D3fWRyPvaZnJfuVrs5WanDxt4vrYnCgI6/BehM 46MQ== X-Gm-Message-State: AOJu0YySLPSZ2Wk8gGkYC+Om5ZUzhiPaEbDhCdZ4tkqoqtGnLjI/G/uj EGnjYlXmUqovv/7MFFpd+vA= X-Google-Smtp-Source: AGHT+IH5Tlq3h4iu5WAA4aadlRX//LfTIMeJ6T7QMkoc1zj0mv+gfP5DnMbdXC+FPY9L9o21xGRDCQ== X-Received: by 2002:a05:600c:220b:b0:406:7029:c4f2 with SMTP id z11-20020a05600c220b00b004067029c4f2mr13012322wml.26.1696850726540; Mon, 09 Oct 2023 04:25:26 -0700 (PDT) Received: from gmail.com (1F2EF237.nat.pool.telekom.hu. [31.46.242.55]) by smtp.gmail.com with ESMTPSA id j31-20020a05600c1c1f00b004068e09a70bsm10946714wms.31.2023.10.09.04.25.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Oct 2023 04:25:25 -0700 (PDT) Sender: Ingo Molnar Date: Mon, 9 Oct 2023 13:25:23 +0200 From: Ingo Molnar To: Joel Fernandes Cc: Peter Zijlstra , linux-kernel@vger.kernel.org, Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , Vineeth Pillai , Suleiman Souhlal , Hsin Yi , Frederic Weisbecker , "Paul E . McKenney" Subject: Re: [PATCH RFC] sched/fair: Avoid unnecessary IPIs for ILB Message-ID: References: <20231005161727.1855004-1-joel@joelfernandes.org> <20231006200129.GJ36277@noisy.programming.kicks-ass.net> <20231008163912.GA2338308@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231008163912.GA2338308@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Joel Fernandes wrote: > > > Fixes: 7fd7a9e0caba ("sched/fair: Trigger nohz.next_balance updates when a CPU goes NOHZ-idle") > > > > Hurm.. does this really warrant a Fixes tag? Afaict nothing is currently > > broken -- this is a pure optimization question, no? > > IMHO it is a breakage as it breaks NOHZ -- a lot of times the ILB kicks > back the CPU stopping the tick out of idle (effectively breaking NOHZ). > The large number of IPIs also wrecks power and it happens only on 6.1 and > after. Having the fixes tag means it will also goto all stable kernels >= > 6.1. Hope that sounds reasonable and thank you for taking a look! So it's basically a fix of a NOHZ performance regression, introduced by 7fd7a9e0caba or so, correct? As long as the fixes have a good hope of being backported with a low amount of overhead, a Fixes: tag for a ~2 years old performance regression is unusual but not unprecedented. We just need to make sure we don't put too much of a burden on the shoulders of -stable maintainers ... Thanks, Ingo