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[23.128.96.34]) by mx.google.com with ESMTPS id y7-20020a1709029b8700b001ce5b6e97fesi1532302plp.45.2023.11.23.09.42.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Nov 2023 09:42:26 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.34 as permitted sender) client-ip=23.128.96.34; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=GBdkpKlp; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.34 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: from out1.vger.email (depot.vger.email [IPv6:2620:137:e000::3:0]) by howler.vger.email (Postfix) with ESMTP id D68CE809B46F; Thu, 23 Nov 2023 09:42:23 -0800 (PST) X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.103.11 at howler.vger.email Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229929AbjKWRmI (ORCPT + 99 others); Thu, 23 Nov 2023 12:42:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44872 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229526AbjKWRmH (ORCPT ); Thu, 23 Nov 2023 12:42:07 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9F099D7D for ; Thu, 23 Nov 2023 09:42:13 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 48AC9C433CA; Thu, 23 Nov 2023 17:42:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1700761333; bh=wybC9NjaiAT+ygrEqCj1gw53nZJCWLLQbHdCCoiI/ig=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=GBdkpKlpgH7AqaOJ59Z5kDNAyx7ZXldXmt4Bp5Candjvu78uXT43J9978CjQuoFhu y5zGm3I6G+0ML0KaJSApyOKMZMP28QzA2SGy/Eu6ASH3htPcjxRkHZYXB54hza6rpF bglT3uCnajq0KnPc/BRZ+8NXKmgMQLrJFoz5yIzdCfUFXX7QDEV3jW+oSEvJ+d6EEy E37lvDGqFnLAXUXnlBJUfQ2pfj33+oAd+kNZ8wWG1JqKDo3bK+dvQfpi/syL+nppPq rvwGzGYw9zlRHoCN9TSftKcjTHyJwChX6qHe9tD66kEjeqNnjsiCiMT1U+K9z5qlnB 1h6u9mWqppoiw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id EEF54CE0D0D; Thu, 23 Nov 2023 09:42:12 -0800 (PST) Date: Thu, 23 Nov 2023 09:42:12 -0800 From: "Paul E. McKenney" To: Qais Yousef Cc: Joel Fernandes , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Boqun Feng , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Andrea Righi , John Stultz , linux-kernel@vger.kernel.org, rcu@vger.kernel.org Subject: Re: [PATCH] rcu: Provide a boot time parameter to enable lazy RCU Message-ID: <4ec83bf4-4c56-4f47-8473-151b57b80840@paulmck-laptop> Reply-To: paulmck@kernel.org References: <20231121205304.315146-1-qyousef@layalina.io> <811b2157-1009-4339-8ff2-0433512f3094@paulmck-laptop> <20231121214415.ovoskvbjarzpxi6e@airbuntu> <8ad4e628-7a88-490c-a54d-df09f851f189@paulmck-laptop> <20231121221556.vtpmboamgszbt3jf@airbuntu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231121221556.vtpmboamgszbt3jf@airbuntu> X-Spam-Status: No, score=-1.3 required=5.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on howler.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (howler.vger.email [0.0.0.0]); Thu, 23 Nov 2023 09:42:24 -0800 (PST) On Tue, Nov 21, 2023 at 10:15:56PM +0000, Qais Yousef wrote: > On 11/22/23 15:26, Paul E. McKenney wrote: > > > > Either way; I'll follow what the crowd wants too :-) > > > > Usually a wise choice. ;-) > > > > But I must defer to the people using it. > > >From Android PoV I'd like to be able to boot with default disabled and allow > people to opt-in. At least for the time being until we have confidence no one > is caught with surprise if this caused unexpected problems. > > In the future it might default to on once it gets wider usage and testing. > > So having a new Kconfig to DEFAULT_OFF sounds good to me to enable a compile > time switch to pick the default with a boot time to further control. > > Which would be my plan for v2 unless I hear another suggestion in the coming > week (where I hope people would have had a chance to look and think about it). Sounds good to me! Silence will be interpreted as assent. ;-) Thanx, Paul > > > No need for the rcu_barrier() then? Only reason why we use the _cb flavour > > > > The module_param() parameters are processed during early boot, before > > the boot CPU has enabled interrupts. In fact, before rcu_init() > > is invoked, which is in turn long before the scheduler has started. > > Calling rcu_barrier() that early is not so good for your kernel's > > actuarial statistics. > > Ah, I missed that it is done that early. > > > > > I am guessing that the module_param_cb() processing happens somewhat > > later in the kernel's lifetime. > > > Thanks! > > -- > Qais Yousef