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

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Date:   Tue, 10 Apr 2018 14:34:34 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        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 Tue, Apr 10, 2018 at 11:10:06PM +0200, Paolo Bonzini wrote:
> On 10/04/2018 22:32, Paul E. McKenney wrote:
> > On Mon, Apr 09, 2018 at 11:42:58AM -0700, Paul E. McKenney wrote:
> >> On Mon, Apr 09, 2018 at 06:50:15PM +0200, Paolo Bonzini wrote:
> >>> "RWM" should be "RMW", and that's more or less the extent to which I
> >>> can claim to change the document. :)  In particular, "Self" is not
> >>> documented and the difference between "Self" and "SV" is not clear
> >>> to me.
> >>>
> >>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> >>
> >> Applied, though without the questions.  ;-)
> >>
> >> "Self" is for things like smp_load_acquire() and smp_store_release()
> >> that order themselves against later and earlier accesses, respectively.
> >> This ordering applies to later/earlier access to all variables, not
> >> just the one that smp_load_acquire()/smp_store_release() accessed.
> >> In contrast, things like smp_mb() order only other accesses, not
> >> themselves.  Or at least it is impossible to proves whether or not they
> >> order themselves because they are not separately visible to other CPUs.
> >>
> >> "SV" is "same variable", which applies to pretty much anything that
> >> accesses a variable, but not to things like smp_mb() which do not.
> >>
> >> Does that help?
> > 
> > On the perhaps naive assumption that silence means assent, how about
> > the following patch?
> 
> Silence meant "I tried thinking of a patch myself, and hadn't come up
> yet with a fully satisfactory one"; that's some kind of assent I guess. :)

;-) ;-) ;-)

> Your patch is certainly an improvement!

Glad it helps, and I have queued it for the next merge window.  Of course,
if a further improvement comes to mind, please do not keep it a secret.  ;-)

							Thanx, Paul

> Thanks,
> 
> Paolo
> 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > commit 818e46e8db6cacb099b8640b7f2945a3151c00ab
> > Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Date:   Tue Apr 10 13:24:19 2018 -0700
> > 
> >     tools/memory-order: Improve key for SELF and SV
> >     
> >     The key for "SELF" was missing completely and the key for "SV" was
> >     a bit obtuse.  This commit therefore adds a key for "SELF" and improves
> >     the one for "SV".
> >     
> >     Reported-by: Paolo Bonzini <pbonzini@...hat.com>
> >     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > 
> > diff --git a/tools/memory-model/Documentation/cheatsheet.txt b/tools/memory-model/Documentation/cheatsheet.txt
> > index c0eafdaddfa4..d502993ac7d2 100644
> > --- a/tools/memory-model/Documentation/cheatsheet.txt
> > +++ b/tools/memory-model/Documentation/cheatsheet.txt
> > @@ -26,4 +26,5 @@ Key:	C:	Ordering is cumulative
> >  	DR:	Dependent read (address dependency)
> >  	DW:	Dependent write (address, data, or control dependency)
> >  	RMW:	Atomic read-modify-write operation
> > -	SV	Same-variable access
> > +	SELF:	Orders self, as opposed to accesses both before and after
> > +	SV:	Orders later accesses to the same variable
> > 
>