linux-kernel - Re: [PATCH 1/5] atomics: add acquire/release/relaxed variants of some atomic operations

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Message-ID: <20150714113801.GK19282@twins.programming.kicks-ass.net>
Date:	Tue, 14 Jul 2015 13:38:01 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Will Deacon <will.deacon@....com>
Cc:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"Waiman.Long@...com" <Waiman.Long@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/5] atomics: add acquire/release/relaxed variants of
 some atomic operations

On Tue, Jul 14, 2015 at 12:31:47PM +0100, Will Deacon wrote:
> #ifndef atomic_add
> #define atomic_add(args...)	(void)atomic_add_return_relaxed(args);
> 
> It would mean a new architecture only has to define a barrier instruction
> and a handful of relaxed atomics for a bare-minimum atomic.h avoiding
> spinlocks.

Look at include/asm-generic/atomic.h, all you need is a cmpxchg().

We could easily change that to be cmpxchg_relaxed() and a few barriers.


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