linux-kernel - Re: [parisc-linux] [patch 15/23] Add cmpxchg

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Date:	Mon, 27 Aug 2007 14:20:17 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	grundler@...isc-linux.org
Cc:	mathieu.desnoyers@...ymtl.ca, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, parisc-linux@...isc-linux.org,
	clameter@....com
Subject: Re: [parisc-linux] [patch 15/23] Add cmpxchg_local to parisc

From: Grant Grundler <grundler@...isc-linux.org>
Date: Mon, 27 Aug 2007 15:04:32 -0600

> Doesn't explain the difference between "local" and "non-local" either.
> Per CPU data should only need memory barriers (in some cases) and
> protection against interrupts (in probably more cases). So I'm not
> understanding why a new set of APIs is needed.
> 
> Can you add a description to Documentation/atomic_ops.txt ?

My understanding is that the local versions can run without
memory barriers.  Only local cpu execution and local interrupt
threads of control can access the variable, and interrupts
force all stores to become visible to the local cpu so an
interrupt can't see the datum from before the atomic update
if one was in progress when the interrupt triggered, and
stuff like that.
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