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From: "Paul E. McKenney" <paulmck@kernel.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Peter Zijlstra <peterz@infradead.org>,
	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
Date: Fri, 22 May 2020 10:43:52 -0700	[thread overview]
Message-ID: <20200522174352.GJ2869@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200522143201.GB32434@rowland.harvard.edu>

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

  reply	other threads:[~2020-05-22 17:43 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-22  0:38 Some -serious- BPF-related litmus tests Paul E. McKenney
2020-05-22  9:44 ` Peter Zijlstra
2020-05-22 10:56   ` Paul E. McKenney
2020-05-22 14:36     ` Alan Stern
2020-05-22 17:45       ` Paul E. McKenney
2020-05-22 14:32   ` Alan Stern
2020-05-22 17:43     ` Paul E. McKenney [this message]
2020-05-22 19:38       ` Andrii Nakryiko
2020-05-24 12:09         ` Akira Yokosawa
2020-05-25 18:31           ` Andrii Nakryiko
2020-05-25 22:01             ` Akira Yokosawa
2020-05-25 23:31               ` Andrii Nakryiko
2020-05-26 10:50                 ` Akira Yokosawa
2020-05-26 14:02                   ` Akira Yokosawa
2020-05-26 20:19                     ` Andrii Nakryiko
2020-05-26 23:00                       ` Akira Yokosawa
2020-05-27  0:09                         ` Andrii Nakryiko
2020-05-26 20:15                   ` Andrii Nakryiko
2020-05-26 22:23                     ` Akira Yokosawa
2020-05-25 11:25         ` Peter Zijlstra
2020-05-25 15:47           ` Paul E. McKenney
2020-05-25 17:02             ` Peter Zijlstra
2020-05-25 17:21               ` Paul E. McKenney
2020-05-25 17:45                 ` Paul E. McKenney
2020-05-28 22:00                 ` Joel Fernandes
2020-05-28 22:16                   ` Peter Zijlstra
2020-05-29  5:14                     ` Andrii Nakryiko
2020-05-29 12:36                       ` Peter Zijlstra
2020-05-29 20:01                         ` Andrii Nakryiko
2020-05-29 20:53                           ` Peter Zijlstra
2020-05-25 14:53         ` Boqun Feng
2020-05-25 18:38           ` Andrii Nakryiko
2020-05-28 21:48             ` Joel Fernandes
2020-05-29  4:38               ` Andrii Nakryiko
2020-05-29 17:23                 ` Joel Fernandes
2020-05-29 20:10                   ` Andrii Nakryiko

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