linux-kernel - Re: [tip:perf/core] tools/perf: Add required memory barriers

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Message-ID: <20131106160720.GK26785@twins.programming.kicks-ass.net>
Date:	Wed, 6 Nov 2013 17:07:20 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vince@...ter.net>
Cc:	mingo@...nel.org, hpa@...or.com, anton@...ba.org,
	mathieu.desnoyers@...ymtl.ca, linux-kernel@...r.kernel.org,
	michael@...erman.id.au, paulmck@...ux.vnet.ibm.com,
	benh@...nel.crashing.org, fweisbec@...il.com, VICTORK@...ibm.com,
	tglx@...utronix.de, oleg@...hat.com, mikey@...ling.org,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] tools/perf: Add required memory barriers

On Wed, Nov 06, 2013 at 03:44:56PM +0100, Peter Zijlstra wrote:
> long head = ((__atomic long)pc->data_head).load(memory_order_acquire);
> 
> coupled with:
> 
> ((__atomic long)pc->data_tail).store(tail, memory_order_release);
> 
> might be the 'right' and proper C11 incantations to avoid having to
> touch kernel macros; but would obviously require a recent compiler.
> 
> Barring that, I think we're stuck with:
> 
> long head = ACCESS_ONCE(pc->data_head);
> smp_rmb();
> 
> ...
> 
> smp_mb();
> pc->data_tail = tail;
> 
> And using the right asm goo for the barriers. That said, all these asm
> barriers should include a compiler barriers (memory clobber) which
> _should_ avoid the worst compiler trickery -- although I don't think it
> completely obviates the need for ACCESS_ONCE() -- uncertain there.

http://software.intel.com/en-us/articles/single-producer-single-consumer-queue/

There's one for icc on x86.
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