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Subject: Re: [RFC][PATCH 2/5] mm: Switch mod_state() to __this_cpu_read()
From: Steven Rostedt <rostedt@goodmis.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Lameter <cl@gentwo.org>, LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Christoph Lameter <cl@linux.com>, Tejun Heo <htejun@gmail.com>
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Date: Tue, 20 Sep 2011 13:08:36 -0400
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On Tue, 2011-09-20 at 18:51 +0200, Thomas Gleixner wrote:

> this_cpu_*() is patently wrong. It should be: random_cpu_*() or
> any_cpu_*(). This way you could have avoided confusion in the first
> place and made it entirely clear what the interfaces are about.

Thinking about this, my vote is for "any_cpu_*()". I initially liked my
own snapshot_cpu_*(), and even random_cpu_*() is humorous. But truly,
the "any_cpu_*()" has the best meaning. As you really don't seem to care
about which CPU you access. Sure you can document something like:

/*
 * Will modify the per cpu data on the current CPU, but there is no
 * guarantee which CPU you may be on, as you can migrate just before
 * or after calling this function. Only the scope of this function
 * will be atomic to the CPU the task is currently on, but no guarantee
 * before or after the function. If you care about that, disable
 * preemption and use the this_cpu_*() variants.
 */

-- Steve