linux-kernel - Re: [RFC][PATCH 0/5] arch: atomic rework

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Message-ID: <CA+55aFwc=1rGngpY1vUUxow11ao4Q36T6u7p9i7m7H6DdNdcRw@mail.gmail.com>
Date:	Mon, 24 Feb 2014 08:40:50 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Richard Biener <richard.guenther@...il.com>
Cc:	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Torvald Riegel <triegel@...hat.com>,
	Will Deacon <will.deacon@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
	David Howells <dhowells@...hat.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"gcc@....gnu.org" <gcc@....gnu.org>
Subject: Re: [RFC][PATCH 0/5] arch: atomic rework

On Mon, Feb 24, 2014 at 8:37 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> So yes, the atomic_read() would be ordered wrt '*ptr' (getting 'q')
> _and_ '**ptr' (getting 'i'), but nothing else - including just the
> aliasing access of dereferencing 'i' directly.

Btw, what CPU architects and memory ordering guys tend to do in
documentation is give a number of "litmus test" pseudo-code sequences
to show the effects and intent of the language.

I think giving those kinds of litmus tests for both "this is ordered"
and "this is not ordered" cases like the above is would be a great
clarification. Partly because the language is going to be somewhat
legalistic and thus hard to wrap your mind around, and partly to
really hit home the *intent* of the language, which I think is
actually fairly clear to both compiler writers and to programmers.

               Linus
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