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Date: Fri, 8 May 2015 16:25:13 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will.deacon@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        David Ahern <dsahern@gmail.com>, Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Question about barriers for ARM on tools/perf/
Message-ID: <20150508142513.GM27504@twins.programming.kicks-ass.net>
References: <20150508140459.GI7862@kernel.org>
 <20150508142107.GA25587@arm.com>
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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..