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

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Message-ID: <20140210114813.GJ9987@twins.programming.kicks-ass.net>
Date:	Mon, 10 Feb 2014 12:48:13 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Will Deacon <will.deacon@....com>,
	Torvald Riegel <triegel@...hat.com>,
	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>,
	"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.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 Fri, Feb 07, 2014 at 10:02:16AM -0800, Paul E. McKenney wrote:
> As near as I can tell, compiler writers hate the idea of prohibiting
> speculative-store optimizations because it requires them to introduce
> both control and data dependency tracking into their compilers.  Many of
> them seem to hate dependency tracking with a purple passion.  At least,
> such a hatred would go a long way towards explaining the incomplete
> and high-overhead implementations of memory_order_consume, the long
> and successful use of idioms based on the memory_order_consume pattern
> notwithstanding [*].  ;-)

Just tell them that because the hardware provides control dependencies
we actually use and rely on them.

Not that I expect they care too much what we do, given the current state
of things.
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