linux-kernel - Re: [PATCH] this_cpu: Use this_cpu_xx in trace_functions

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Message-ID: <alpine.DEB.1.10.0910131043460.8088@gentwo.org>
Date:	Tue, 13 Oct 2009 10:45:39 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...e.hu>, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] this_cpu: Use this_cpu_xx in trace_functions_graph.c

On Tue, 13 Oct 2009, Tejun Heo wrote:

> Oh... one question tho.  I used __this_cpu_*() as other conversions
> but I think we should be using the version without the underscores.
> The relationship between get_cpu_var() and __get_cpu_var() is
> different from the one between this_cpu_*() and __this_cpu_*().

For operations like inc/add/dec/sub you need to use the version with __
otherwise the arches that do not support these operations will have to
generate useless expensive code that disables / reenables preempt.

For this_cpu_ptr / __this_cpu_ptr it does not matter. this_cpu_ptr gives
you additional checks.

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