Date: Wed, 31 Oct 2012 00:44:02 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com,
        dipankar@in.ibm.com, akpm@linux-foundation.org,
        mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com,
        tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu,
        dhowells@redhat.com, edumazet@google.com, darren@dvhart.com,
        fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org,
        joe.korty@ccur.com
Subject: Re: [PATCH tip/core/rcu 0/2] v2 Add callback-free CPUs
Message-ID: <20121031074402.GV3027@linux.vnet.ibm.com>
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On Wed, Oct 31, 2012 at 08:25:21AM +0100, Peter Zijlstra wrote:
> On Tue, 2012-10-30 at 20:45 -0700, Paul E. McKenney wrote:
> > This commit therefore adds the ability
> > for selected CPUs ("rcu_nocbs=" boot parameter) to have their
> > callbacks
> > offloaded to kthreads, inspired by Joe Korty's and Jim Houston's JRCU.
> > If the "rcu_nocb_poll" boot parameter is also specified, these
> > kthreads
> > will do polling, removing the need for the offloaded CPUs to do
> > wakeups. 
> 
> How much pain to make that dynamically configurable?

A fair amount of pain, though I do hope to make it runtime configurable
at some point.  Known problems include races between changes in the
nocb configuration, rcu_barrier(), grace-period initialization, and
CPU hotplug.  Should be solvable, but want to get the other bugs out of
the way first.

							Thanx, Paul

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