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

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Message-ID: <4AD49559.5050707@kernel.org>
Date:	Tue, 13 Oct 2009 23:57:29 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Christoph Lameter <cl@...ux-foundation.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

Christoph Lameter wrote:
> 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.

Yes, you're right.  The naming scheme in percpu sucks really hard.
The subtle differences among [__]get_cpu_var(), [__]this_cpu_ptr() and
other this_cpu ops.  Arghhhhhh.......

-- 
tejun
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