Date: Wed, 23 Feb 2011 13:22:02 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
        Steven Rostedt <rostedt@goodmis.org>,
        Frederic Weisbecker <fweisbec@gmail.com>, linux-kernel@vger.kernel.org,
        mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com,
        akpm@linux-foundation.org, josh@joshtriplett.org, niv@us.ibm.com,
        tglx@linutronix.de, peterz@infradead.org, Valdis.Kletnieks@vt.edu,
        dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com,
        "Paul E. McKenney" <paul.mckenney@linaro.org>
Subject: Re: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq
 to kthread
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On Wed, 23 Feb 2011, Paul E. McKenney wrote:

> These do introduce redundant preempt_disable()/preempt_enable() calls, but
> this is not on a fastpath, so should be OK, and the improved readability
> is certainly nice.  The read and the write do need to happen on the same
> CPU, FWIW.

this_cpu_xxx only use preempt_enable/disable() on platforms that do not
support per cpu atomic instructions. On x86 no preempt enable/disable will
be inserted.

You can also use the __this_cpu_xxx operations which never add preempt
disable/enable because they expect the caller to deal with preemption.
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