linux-kernel - Re: [PATCH] memory-model: fix cheat sheet typo

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Message-ID: <70348608-e695-1977-d34e-d7d66b07ad25@redhat.com>
Date:   Wed, 11 Apr 2018 19:06:36 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Will Deacon <will.deacon@....com>,
        Boqun Feng <boqun.feng@...il.com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Howells <dhowells@...hat.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Akira Yokosawa <akiyks@...il.com>
Subject: Re: [PATCH] memory-model: fix cheat sheet typo

On 11/04/2018 18:31, Peter Zijlstra wrote:
>>>                                    Prior Operation   Subsequent Operation
>>>                                    ---------------   ---------------------
>>>                                    R  W  RMW  SV     R  W  DR  DW  RMW  SV
>>>                                    -  -  ---  --     -  -  --  --  ---  --
>>> smp_store_mb()                     Y  Y    Y   Y      Y  Y   Y   Y   Y   Y
> I'm not sure about that, the generic version of that reads:
> 
> include/asm-generic/barrier.h:#define __smp_store_mb(var, value)
>     do { WRITE_ONCE(var, value); __smp_mb(); } while (0)
> 
> Which doesn't not have an smp_mb() before, so it doesn't actually order
> prior; or I'm failing to read the table wrong.

You're not, even better reason to document it. :)  I was going from
memory for the x86 version.

I'll start tomorrow on fixes to the current document, while we discuss
the split format and what to do about cumulativity and propagation.

Paolo