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 6197CC433DF for ; Fri, 22 May 2020 17:43:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2B6E3207BC for ; Fri, 22 May 2020 17:43:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590169434; bh=t22SyB9/K0m7E486hZD+8n3eS0aL0e1D5tiaHegV7t4=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=mM+gygvAsHR/K8816fdddyz/XUGwaHw4SNx7cL7Th8OFrOejCr764FuSaPcXsPFc5 IOeDfWPbEvwYkZXGA1nGqggDZowSpGDOPhrmH3YsVFYPP4RjcwkxamYmQHlIqRYZW7 HI281d/sCVHM4c0tAfKeQ2QjrvmQ64YA+3zFkyrM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730780AbgEVRnx (ORCPT ); Fri, 22 May 2020 13:43:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:51894 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726373AbgEVRnx (ORCPT ); Fri, 22 May 2020 13:43:53 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (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 C4E5620723; Fri, 22 May 2020 17:43:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590169432; bh=t22SyB9/K0m7E486hZD+8n3eS0aL0e1D5tiaHegV7t4=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=FbvkIrVI+T2eCWT0T7gRxnb98/8VdBn4hzMhVK3rF9tB4lYEISVUrrayGEoSOG25L 4BK+yKfkU4EyB9swUyvf9VivrR5ydvB7E5qmyVnKp5RM1l4MO88lptxGLiPYSbL1Mm H5mYORDCqyVUzKjzY3buBkk1ShuYVqCYoKDrX78Y= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id AFA063522E41; Fri, 22 May 2020 10:43:52 -0700 (PDT) Date: Fri, 22 May 2020 10:43:52 -0700 From: "Paul E. McKenney" To: Alan Stern Cc: Peter Zijlstra , parri.andrea@gmail.com, will@kernel.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com, dlustig@nvidia.com, joel@joelfernandes.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, andriin@fb.com Subject: Re: Some -serious- BPF-related litmus tests Message-ID: <20200522174352.GJ2869@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200522003850.GA32698@paulmck-ThinkPad-P72> <20200522094407.GK325280@hirez.programming.kicks-ass.net> <20200522143201.GB32434@rowland.harvard.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200522143201.GB32434@rowland.harvard.edu> 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 Fri, May 22, 2020 at 10:32:01AM -0400, Alan Stern wrote: > On Fri, May 22, 2020 at 11:44:07AM +0200, Peter Zijlstra wrote: > > On Thu, May 21, 2020 at 05:38:50PM -0700, Paul E. McKenney wrote: > > > Hello! > > > > > > Just wanted to call your attention to some pretty cool and pretty serious > > > litmus tests that Andrii did as part of his BPF ring-buffer work: > > > > > > https://lore.kernel.org/bpf/20200517195727.279322-3-andriin@fb.com/ > > > > > > Thoughts? > > > > I find: > > > > smp_wmb() > > smp_store_release() > > > > a _very_ weird construct. What is that supposed to even do? > > Indeed, it looks like one or the other of those is redundant (depending > on the context). Probably. Peter instead asked what it was supposed to even do. ;-) > Also, what use is a spinlock that is accessed in only one thread? Multiple writers synchronize via the spinlock in this case. I am guessing that his larger 16-hour test contended this spinlock. > Finally, I doubt that these tests belong under tools/memory-model. > Shouldn't they go under the new Documentation/ directory for litmus > tests? And shouldn't the patch update a README file? Agreed, and I responded to that effect to his original patch: https://lore.kernel.org/bpf/20200522003433.GG2869@paulmck-ThinkPad-P72/ Thanx, Paul