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

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Message-ID: <CA+55aFwTrt_6m1inNHQkk74i7uPkHNnacwHiBgioZSXieAs5Sw@mail.gmail.com>
Date:	Sat, 15 Feb 2014 10:49:11 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Torvald Riegel <triegel@...hat.com>
Cc:	Paul McKenney <paulmck@...ux.vnet.ibm.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 Sat, Feb 15, 2014 at 9:45 AM, Torvald Riegel <triegel@...hat.com> wrote:
>
> I think a major benefit of C11's memory model is that it gives a
> *precise* specification for how a compiler is allowed to optimize.

Clearly it does *not*. This whole discussion is proof of that. It's
not at all clear, and the standard apparently is at least debatably
allowing things that shouldn't be allowed. It's also a whole lot more
complicated than "volatile", so the likelihood of a compiler writer
actually getting it right - even if the standard does - is lower.
They've gotten "volatile" wrong too, after all (particularly in C++).

           Linus
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