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 6FBBEC3DA78 for ; Sat, 14 Jan 2023 17:42:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229932AbjANRmM (ORCPT ); Sat, 14 Jan 2023 12:42:12 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46132 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230201AbjANRmK (ORCPT ); Sat, 14 Jan 2023 12:42:10 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 70FA1B75D for ; Sat, 14 Jan 2023 09:42:08 -0800 (PST) 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 dfw.source.kernel.org (Postfix) with ESMTPS id 0690D60C02 for ; Sat, 14 Jan 2023 17:42:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 56357C433D2; Sat, 14 Jan 2023 17:42:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1673718127; bh=DBr2dfvAo+ffnzn+Wni3YbAR6iSPBoC4vY82PM0Jahg=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=OaBN2HYJ+O5q3up7QbqPgBXjnFumGzmZokN2JvCmC/wkcWtH1lMZx3YLrNFCuQILj S8ZjwuTlMET2EarScsGrD6+gfiI8l9nqnHVbNJwww5AU2fic3CNEIpTZg+NEDK9Dot nvl96TB0s7g6MPatHn0QKc20s7KoQGiICm6G4I8L4RRCUFVm5y7qav4K5ABUzJlJtY k9J62GoA1BGPPb0HUAJm8fRi9A2P5Zh96Ngytm70FIIwfAZ7MxYNUyvVlxXilABMG4 TV3q7CistXZ1serN7wn1PCqlgHtITB2mTV7ddjJH5x0304BJgc354XNKpvsOycG7vo sy9NHC9+AVZ0w== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id F1AB55C0AF8; Sat, 14 Jan 2023 09:42:06 -0800 (PST) Date: Sat, 14 Jan 2023 09:42:06 -0800 From: "Paul E. McKenney" To: Jonas Oberhauser Cc: Alan Stern , Peter Zijlstra , "parri.andrea" , will , "boqun.feng" , npiggin , dhowells , "j.alglave" , "luc.maranget" , akiyks , dlustig , joel , urezki , quic_neeraju , frederic , Kernel development list Subject: Re: Internal vs. external barriers (was: Re: Interesting LKMM litmus test) Message-ID: <20230114174206.GD2948950@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220921173109.GA1214281@paulmck-ThinkPad-P17-Gen-1> <114ECED5-FED1-4361-94F7-8D9BC02449B7> <06a8aef7eb8d46bca34521a80880dae3@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <06a8aef7eb8d46bca34521a80880dae3@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 13, 2023 at 05:05:11PM +0000, Jonas Oberhauser wrote: > -----Original Message----- > From: Alan Stern [mailto:stern@rowland.harvard.edu] > Sent: Friday, January 13, 2023 5:38 PM > > > Strictly speaking, this is not right. It should say: For each process/CPU/task/whatever, an RCU grace period includes at least one moment in time during which that process is not within an RCU read-side critical section. There does not have to be any single moment during which no processes are executing a critical section. > > I see. I guess the other thing is more like a quiescent period. "Quiescent period" was in fact my original name for "grace period" back in the day, but a chorus of objections eventually prompted me to instead label it a "grace period". Perhaps you have given an improved rationale for their objections. ;-) > I > think the fact that RCU/safe memory reclamation(SMR) don't require a > quiescent period is an important distinction, and even though we have > our own SMR I never thought too deeply about this distinction. If you want non-abysmal performance and scalability on modern hardware, the distinction is critically important. After all, the speed of light really is finite, and atoms are of non-zero size. And to the complete surprise of my forty-years-ago self, these laws of physics seriously constrain modern computing devices. Thanx, Paul