linux-kernel - Re: [PATCH RFC] rcu: Make rcu

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Message-ID: <4F674178.90607@linux.vnet.ibm.com>
Date:	Mon, 19 Mar 2012 19:53:52 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
	patches@...aro.org
Subject: Re: [PATCH RFC] rcu: Make rcu_barrier() less disruptive


Hi Paul,

On 03/15/2012 10:18 PM, Paul E. McKenney wrote:

> The rcu_barrier() primitive interrupts each and every CPU, registering
> a callback on every CPU.  Once all of these callbacks have been invoked,
> rcu_barrier() knows that every callback that was registered before
> the call to rcu_barrier() has also been invoked.
> 
> However, there is no point in registering a callback on a CPU that
> currently has no callbacks, most especially if that CPU is in a
> deep idle state.  This commit therefore makes rcu_barrier() avoid
> interrupting CPUs that have no callbacks.  Doing this requires reworking
> the handling of orphaned callbacks, otherwise callbacks could slip through
> rcu_barrier()'s net by being orphaned from a CPU that rcu_barrier() had
> not yet interrupted to a CPU that rcu_barrier() had already interrupted.
> This reworking was needed anyway to take a first step towards weaning
> RCU from the CPU_DYING notifier's use of stop_cpu().
> 

s/stop_cpu()/stop_machine() ?


Thank you for doing this! :-)

> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 


Regards,
Srivatsa S. Bhat
IBM Linux Technology Center

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