From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Stern Subject: Re: Some -serious- BPF-related litmus tests Date: Fri, 22 May 2020 10:32:01 -0400 Message-ID: <20200522143201.GB32434@rowland.harvard.edu> References: <20200522003850.GA32698@paulmck-ThinkPad-P72> <20200522094407.GK325280@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20200522094407.GK325280@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra Cc: "Paul E. McKenney" , 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 List-Id: linux-arch.vger.kernel.org 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). Also, what use is a spinlock that is accessed in only one thread? 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? Alan From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from netrider.rowland.org ([192.131.102.5]:39221 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1729868AbgEVOcC (ORCPT ); Fri, 22 May 2020 10:32:02 -0400 Date: Fri, 22 May 2020 10:32:01 -0400 From: Alan Stern Subject: Re: Some -serious- BPF-related litmus tests Message-ID: <20200522143201.GB32434@rowland.harvard.edu> References: <20200522003850.GA32698@paulmck-ThinkPad-P72> <20200522094407.GK325280@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200522094407.GK325280@hirez.programming.kicks-ass.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: "Paul E. McKenney" , 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 Message-ID: <20200522143201.ug8rvKVxtCTtFirQznpDsLCguQe3_dZTUPXVHOnzjlo@z> 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). Also, what use is a spinlock that is accessed in only one thread? 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? Alan