From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 1/4] arch: local64_t
Date: Fri, 21 May 2010 15:52:29 +0100
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References: <20100521135944.884367426@chello.nl> <20100521134205.781916350@chello.nl>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: dhowells@redhat.com, Ingo Molnar <mingo@elte.hu>, Paul Mackerras <paulus@samba.org>, Arnaldo Carvalho de Melo <acme@infradead.org>, Frederic Weisbecker <fweisbec@gmail.com>, Steven Rostedt <rostedt@goodmis.org>, David Miller <davem@davemloft.net>, Paul Mundt <lethal@linux-sh.org>, Will Deacon <will.deacon@arm.com>, Deng-Cheng Zhu <dengcheng.zhu@gmail.com>, LKML <linux-kernel@vger.kernel.org>, linux-arch@vger.kernel.org



Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> + * This is the default implementation, which uses atomic64_t.  Which is
> + * rather pointless.  The whole point behind local64_t is that some processors
> + * can perform atomic adds and subtracts in a manner which is atomic wrt IRQs
> + * running on this CPU.  local64_t allows exploitation of such capabilities.

Interesting...  What FRV does in atomic64-ops.S should probably be rebranded
local64_t, and atomic64_t ops be based on that in non-SMP mode.

What I did on FRV was to emulate LL/ST instructions using some of the
excessive numbers of conditional bits to do so - but it only works on UP
systems.

David