linux-kernel - Re: [PATCH 1/8] membarrier: Document why membarrier() works

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Date:   Wed, 16 Jun 2021 09:30:50 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH 1/8] membarrier: Document why membarrier() works

On Wed, Jun 16, 2021 at 02:00:37PM +1000, Nicholas Piggin wrote:
> Excerpts from Andy Lutomirski's message of June 16, 2021 1:21 pm:
> > We had a nice comment at the top of membarrier.c explaining why membarrier
> > worked in a handful of scenarios, but that consisted more of a list of
> > things not to forget than an actual description of the algorithm and why it
> > should be expected to work.
> > 
> > Add a comment explaining my understanding of the algorithm.  This exposes a
> > couple of implementation issues that I will hopefully fix up in subsequent
> > patches.
> > 
> > Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> > Cc: Nicholas Piggin <npiggin@...il.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Andy Lutomirski <luto@...nel.org>
> > ---
> >  kernel/sched/membarrier.c | 55 +++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 55 insertions(+)
> > 
> > diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
> > index b5add64d9698..3173b063d358 100644
> > --- a/kernel/sched/membarrier.c
> > +++ b/kernel/sched/membarrier.c
> > @@ -7,6 +7,61 @@
> >  #include "sched.h"
> >  
> 
> Precisely describing the orderings is great, not a fan of the style of the
> comment though.

I'm with Nick on that; I can't read it :/ It only makes things more
confusing. If you want precision, English (or any natural language) is
your enemy.

To describe ordering use the diagrams and/or litmus tests.