linux-kernel - Re: [RFC/PATCH 2/5] kernel_cpustat: convert to atomic 64-bit accessors

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Message-ID: <20130221215850.GC17833@n2100.arm.linux.org.uk>
Date:	Thu, 21 Feb 2013 21:58:50 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Kevin Hilman <khilman@...aro.org>,
	Mats Liljegren <mats.liljegren@...a.com>,
	linaro-dev@...ts.linaro.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC/PATCH 2/5] kernel_cpustat: convert to atomic 64-bit
	accessors

On Thu, Feb 21, 2013 at 10:53:07PM +0100, Frederic Weisbecker wrote:
> That too should be kcpustat_this_cpu_set(), or kcpustat_this_cpu_add()
> FWIW. But we probably don't need the overhead of atomic_add() that
> does a LOCK.
> atomic_set(var, atomic_read(var) + delta) would be better. All we need

You mean atomic64_set() and atomic64_read().  Looking at the generic
version in lib/atomic64.c, atomic64_add() is cheaper for 32-bit arches
because it doesn't involve taking the lock twice.
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