linux-kernel - Re: [PATCH 3/3] ring-buffer: add design document

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Date:	Thu, 11 Jun 2009 08:51:07 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Theodore Tso <tytso@....edu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"Martin J. Bligh" <mbligh@...igh.org>,
	Christoph Hellwig <hch@...radead.org>,
	Li Zefan <lizf@...fujitsu.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>
Subject: Re: [PATCH 3/3] ring-buffer: add design document

On Thu, 2009-06-11 at 03:53 +0800, Steven Rostedt wrote:
> +
> +cmpxchg - hardware assisted atomic transaction that performs the following:
> +
> +   A = B iff previous A == C
> +
> +   R = cmpxchg(A, C, B) is saying that we replace A with B if and only if
> +      current A is equal to C, and we put the old (current) A into R
> +
> +   R gets the previous A regardless if A is updated with B or not.
> +
> +   To see if the update was successful a compare of R == C may be used.

As far as I know, some architectures have no hardware assisted (NMI
safe) cmpxchg. Is it OK to use cmpxchg in architecture-independent code?

Best Regards,
Huang Ying


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