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Date: Tue, 20 Sep 2011 09:57:32 -0500 (CDT)
From: Christoph Lameter <cl@gentwo.org>
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To: Valdis.Kletnieks@vt.edu
cc: Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [RFC][PATCH 0/5] Introduce checks for preemptable code for
 this_cpu_read/write()
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On Tue, 20 Sep 2011, Valdis.Kletnieks@vt.edu wrote:

> On Mon, 19 Sep 2011 23:06:17 EDT, Steven Rostedt said:
>
> > It is really confusing to know which version to use. I'm confused by the
> > this_cpu_*() compared with __this_cpu_*(). I'm guessing that most places
> > should use __this_cpu*(). But really this_cpu() should be the default,
> > and the places that can have it outside of preemption should have
> > another name. Maybe use the raw_this_cpu() or safe_this_cpu(), as there
> > is an irqsafe_this_cpu(). Maybe make a preemptsafe_cpu_*(). There should
> > only be a very few locations that are OK to have preemption enabled when
> > calling the this_cpu() code. Lets have those have the funny names and
> > not be the default "this_cpu_*()".

this_cpu_xx functions are made for those locations that have
preemption enabled. If you can use those function (classic case is a
per cpu counter increment in the network subsystem) then you can avoid
preempt disable/enable or get_cpu/put_cpu.