Date: Wed, 23 Feb 2011 13:19:15 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
To: Steven Rostedt <rostedt@goodmis.org>
cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.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, Steven Rostedt wrote:

> On Wed, 2011-02-23 at 12:29 -0600, Christoph Lameter wrote:
>
> > Right if the kthread context can be rescheduled then either preemption
> > needs to be disabled to guarantee that all three access the same per cpu
> > area data or the code needs to be changed in such a way that a this_cpu
> > RMW instructions can do the mods in one go.
>
> Are you suggesting a this_cpu_atomic_inc()?

this_cpu_inc is already percpu atomic. On x86 it is an instruction that
cannot be interrupted nor preempted while in progress.

There is also this_cpu_cmpxchg() which could be used to do some more
advanced tricks.

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