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 6CBC6C4332F for ; Tue, 20 Dec 2022 19:01:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229619AbiLTTBZ (ORCPT ); Tue, 20 Dec 2022 14:01:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45864 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233953AbiLTTBJ (ORCPT ); Tue, 20 Dec 2022 14:01:09 -0500 Received: from smtpout.efficios.com (smtpout.efficios.com [167.114.26.122]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 001371BE8E; Tue, 20 Dec 2022 11:01:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1671562865; bh=/0Oi+DHifoIwufO7cQbm0fgGedMbH1T10vLjdK1ObKI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=DxxUoHNLNUIpL8TX8lq5TJKcZAC0pnvtN0HObWtd2d13Ujtje7O0DyDmd1tsPJ95r kNUFOHx1ZXGpm2yT0mTVqaKcd7Xo83s1Q3b3hrGHXdjjCbgPipQRgpZFxdj1hLrlJT FzuQO7d65d0kI1bsFuLe3cZu4hGQEqEPuEVMRgF2LEkYqVj7v9w5ZXUNrBaAe3TTb7 MfN+hZF2LEbfV+Hd3b8Y8lRL5QI1b/D4Fn4vAtlJp0o77eG8wUsK6DrSmBvdZ8uy0E BlZyTrtRRunMU9rJK2Ym1XUuvE8J9lYDcpl0Ub0Tm6KCmLgBDoGS+34sKXWoIA9YZk J7kptzFA5gthw== Received: from [10.1.0.30] (192-222-188-97.qc.cable.ebox.net [192.222.188.97]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4Nc5Wj1HFCzbnm; Tue, 20 Dec 2022 14:01:05 -0500 (EST) Message-ID: <5bd5ee4a-710a-96bc-abe8-772b2e60f478@efficios.com> Date: Tue, 20 Dec 2022 14:01:30 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0 Subject: Re: [RFC 0/2] srcu: Remove pre-flip memory barrier Content-Language: en-US To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, Josh Triplett , Lai Jiangshan , "Paul E. McKenney" , rcu@vger.kernel.org, Steven Rostedt References: <6438d903-ab97-48c7-c338-9f0bc2686f94@efficios.com> <7A9876BA-C375-42A7-A5C9-FD940D2898D7@joelfernandes.org> From: Mathieu Desnoyers In-Reply-To: <7A9876BA-C375-42A7-A5C9-FD940D2898D7@joelfernandes.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022-12-20 13:29, Joel Fernandes wrote: > > I do want to finish my memory barrier studies of SRCU over the holidays since I have been deep in the hole with that already. Back to the post flip memory barrier here since I think now even that might not be needed… I strongly suspect the memory barrier after flip is useless for the same reasons I mentioned explaining why the barrier before the flip is useless. However, we need to double-check that we have memory barriers at the beginning and end of synchronize_srcu, and between load of "unlock" counters and load of "lock" counters. Where is the barrier at the beginning of synchronize_srcu ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com