linux-kernel - Re: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE

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Message-ID: <alpine.DEB.2.00.1102231320050.4823@router.home>
Date:	Wed, 23 Feb 2011 13:22:02 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq
 to kthread

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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