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 0767CC433E0 for ; Thu, 14 May 2020 22:49:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C59F820748 for ; Thu, 14 May 2020 22:49:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589496556; bh=2x2Ujz7VHOzikXbLX1adBO5wcVnnvE/Q1xNwgIXhZ+U=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=D+z0jn5r1jFCJysvbdK96ZR9303kGuxqxudw58eZ5w2UA3i9eiMBrscECwvh0aIdz ehKn/zkZ9LqGnzuO/pgScg22jaZivYXe9Ffa3Q6mejg9sdDVWYvAJnrvzaj4gPst6h E8nCED9MlvQ/5q1baKFYqMylQPFk/QpvihGOdfig= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728881AbgENWtQ (ORCPT ); Thu, 14 May 2020 18:49:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:48264 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728229AbgENWtP (ORCPT ); Thu, 14 May 2020 18:49:15 -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 BF4ED20709; Thu, 14 May 2020 22:49:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589496555; bh=2x2Ujz7VHOzikXbLX1adBO5wcVnnvE/Q1xNwgIXhZ+U=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=oU6UtzuR7g9P17xnxg9EKR2vFAw+1l6sXOfg0Ei2AVVrF3w2oZqrC2NK7fm88UcGT 0xlpVT1MnNvBBe1xWNksUyQOY4RQwywZxY5zK3ew2xn++RP8p3thtyajq35qmVPpGs oBkwr3rI4x43LDCCJAzV276pH8a1GZ4yekzGS+co= Date: Fri, 15 May 2020 00:49:13 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: LKML , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , Josh Triplett Subject: Re: [PATCH 07/10] rcu: Temporarily assume that nohz full CPUs might not be NOCB Message-ID: <20200514224912.GB4071@lenoir> References: <20200513164714.22557-1-frederic@kernel.org> <20200513164714.22557-8-frederic@kernel.org> <20200513182527.GU2869@paulmck-ThinkPad-P72> <20200513230827.GC18303@lenoir> <20200514155032.GN2869@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200514155032.GN2869@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 Thu, May 14, 2020 at 08:50:32AM -0700, Paul E. McKenney wrote: > On Thu, May 14, 2020 at 01:08:28AM +0200, Frederic Weisbecker wrote: > > On Wed, May 13, 2020 at 11:25:27AM -0700, Paul E. McKenney wrote: > > > On Wed, May 13, 2020 at 06:47:11PM +0200, Frederic Weisbecker wrote: > > > > So far nohz_full CPUs had to be nocb. This requirement may change > > > > temporarily as we are working on preparing RCU to be able to toggle the > > > > nocb state of a CPU. Once that is done and nohz_full can be toggled as > > > > well dynamically, we'll restore that initial requirement. > > > > > > Would it simplify anything to make the CPU exit nohz_full first and > > > then exit rcu_nocb and vice versa in the other direction? That way the > > > assumption about nohz_full CPUs always being rcu_nocb could remain while > > > still allowing runtime changes to both states. > > > > That's the future plan but for now nohz_full can't even be exited yet. > > RCU is unlucky enough to be chosen as the starting point of this whole work :-) > > But testing could still start with CPUs marked rcu_nocb but not marked > nohz_full, right? Ah! That makes sense indeed. I should indeed restrict de-offloading to CPUs that are not nohz_full. > I must confess that I am a bit concerned about the increase in state space. Yeah good point! > Fair point, but I am also concerned about the welfare of the people > working on it. ;-) Fair enough! :-)