From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: Some -serious- BPF-related litmus tests Date: Fri, 22 May 2020 10:43:52 -0700 Message-ID: <20200522174352.GJ2869@paulmck-ThinkPad-P72> References: <20200522003850.GA32698@paulmck-ThinkPad-P72> <20200522094407.GK325280@hirez.programming.kicks-ass.net> <20200522143201.GB32434@rowland.harvard.edu> Reply-To: paulmck@kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20200522143201.GB32434@rowland.harvard.edu> Sender: linux-kernel-owner@vger.kernel.org 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 List-Id: linux-arch.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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: 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 Date: Fri, 22 May 2020 10:43:52 -0700 From: "Paul E. McKenney" 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> Sender: linux-arch-owner@vger.kernel.org List-ID: 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 Message-ID: <20200522174352.zwNjPlVcalqH4WBqdSurl5NEpBOh_9G0kJmjpbYY9yo@z> 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