linux-kernel - Re: Question about barriers for ARM on tools/perf/

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Date:	Fri, 8 May 2015 16:25:13 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Question about barriers for ARM on tools/perf/

On Fri, May 08, 2015 at 03:21:08PM +0100, Will Deacon wrote:
> Wouldn't it be better to go the other way, and use compiler builtins for
> the memory barriers instead of relying on the kernel? It looks like the
> perf_mmap__{read,write}_head functions are basically just acquire/release
> operations and could therefore be implemented using something like
> __atomic_load_n(&pc->data_head, __ATOMIC_ACQUIRE) and
> __atomic_store_n(&pc->data_tail, tail, __ATOMIC_RELEASE).

He wants to do smp refcounting, which needs atomic_inc() /
atomic_inc_non_zero() / atomic_dec_return() etc..
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