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

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Message-ID: <20110223193933.GW2163@linux.vnet.ibm.com>
Date:	Wed, 23 Feb 2011 11:39:33 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux.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, Feb 23, 2011 at 01:22:02PM -0600, Christoph Lameter wrote:
> 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.

Those make a lot of sense in this case, as I need to use __get_cpu_var()
anyway.

Thank you for all the info!

							Thanx, Paul
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