Date: Wed, 23 Feb 2011 12:45:28 -0800
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Christoph Lameter <cl@linux.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
        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
Message-ID: <20110223204528.GZ2163@linux.vnet.ibm.com>
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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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