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 87C19C433F5 for ; Thu, 14 Apr 2022 19:42:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345854AbiDNToh (ORCPT ); Thu, 14 Apr 2022 15:44:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47108 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345839AbiDNTod (ORCPT ); Thu, 14 Apr 2022 15:44:33 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C3ABBED911; Thu, 14 Apr 2022 12:42:07 -0700 (PDT) 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 7E4BBB8293E; Thu, 14 Apr 2022 19:42:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 288D9C385A1; Thu, 14 Apr 2022 19:42:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1649965325; bh=hDxs4KU5mP0gUbUSd9NQEU3TT/tQrqWlLrCusTnSiDE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=e0S++tFyje2Ax3Sd6Dn6oBMdYfQ4kIzJT5kztcfSN5YMje8JCIXlePRTMPLiFQSZE DjszZ1ptDiasgbtmhxEBJl09Hk/C2h/ACqEziRc99npFjcEvrzOxiEsbVAAPDXtq6N nDOSh2EHPg8JXrN8xCAVa4fYtwtkcUa6hgsTRqzslAtf64UV4y8M8HJYR60f6c7Omg DaCJkv2mDjiGLPKLJ25dT3c/tjcJ8SoAqXfGT7KVaUp95TfwshCFuNrt7GvAmbRy5W nBDFD6mhO3cuYupb7bX4VZDvYnSrnsIA7VPuZm6qz3seuQ239zKWl/UuMDQbMkRxJM +x1uEwU8EBxvA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id BDD065C0144; Thu, 14 Apr 2022 12:42:04 -0700 (PDT) Date: Thu, 14 Apr 2022 12:42:04 -0700 From: "Paul E. McKenney" To: Joel Fernandes Cc: LKML , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , rcu , Steven Rostedt , Frederic Weisbecker Subject: Re: [PATCH RFC] rcu/nocb: Provide default all-CPUs mask for RCU_NOCB_CPU=y Message-ID: <20220414194204.GU4285@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220408155002.GF4285@paulmck-ThinkPad-P17-Gen-1> <20220408174908.GK4285@paulmck-ThinkPad-P17-Gen-1> <20220408205440.GL4285@paulmck-ThinkPad-P17-Gen-1> <20220411154109.GX4285@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 14, 2022 at 07:19:48PM +0000, Joel Fernandes wrote: > On Mon, Apr 11, 2022 at 08:41:09AM -0700, Paul E. McKenney wrote: > [..] > > > > [4] All CPUs are offloaded at boot, and any CPU can be de-offloaded > > > > and offloaded at runtime. This is the same behavior that > > > > you would currently get with CONFIG_RCU_NOCB_CPU_ALL=n and > > > > rcu_nocbs=0-N. > > > > > > Yes, this is the behavior I intend. So then there would not be a need > > > to pass a mask (and I suspect for a large number of users, it > > > simplifies boot params). > > > > Very good, and from what I can see, this should work for everyone. > > Just to clarify, what I am going to do is, if this new option =y, then > rcu_nocbs effectively wont do anything. i.e. All CPUs are offloaded at boot. > Let me know if we are not on the same page about it though. I do feel that is > a sensible choice given =y. If we are on same page, please ignore my comment. I was assuming that the rcu_nocbs=??? for non-empty "???" would override the CONFIG_RCU_NOCB_CPU_ALL=y. If you choose not to do that, shouldn't you at least issue some sort of diagnostic? After all, the sysadmin gave a kernel-boot parameter asking the code to do something and the code is choosing not to do that something. Of course, such a sysadmin might want the CONFIG_RCU_NOCB_CPU_ALL=y Kconfig option to affect only the default, that is, when no rcu_nocbs kernel boot parameter is specified. This would change the second "[4]" in my original table to "[2]". Thoughts? > > > > I believe that Steve Rostedt's review would carry weight for ChromeOS, > > > > however, I am suffering a senior moment on the right person for Android. > > > > > > I think for Android, Kalesh Singh is in the kernel team and Tim Murray > > > is the performance lead. They could appropriately represent their RCU > > > needs. > > > > Sounds good! Please collect a Reviewed-by from one or both of them. > > Ok. Thanx, Paul