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

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Message-ID: <20110223204528.GZ2163@linux.vnet.ibm.com>
Date:	Wed, 23 Feb 2011 12:45:28 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	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 01:24:34PM -0600, Christoph Lameter wrote:
> On Wed, 23 Feb 2011, Paul E. McKenney wrote:
> 
> > Reschedules can happen in this case due to CPU hotplug events.  :-(
> 
> Lockout cpu hotplug instead of disabling interrupts? Systems that support
> cpu hotplug in hardware are rare and so the cpu hotplug locking may be
> become noop.

Good point!

However, the local_irq_save() is doing two things here: (1) blocking
CPU hotplug and (2) synchronizing with concurrent invocations of
invoke_rcu_cpu_kthread() from irq handlers.

							Thanx, Paul
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