linux-kernel - Re: [PATCH v2 15/45] rcu: Use get/put_online_cpus

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Message-ID: <1372258271.18733.256.camel@gandalf.local.home>
Date:	Wed, 26 Jun 2013 10:51:11 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	David Laight <David.Laight@...LAB.COM>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	peterz@...radead.org, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, walken@...gle.com, mingo@...nel.org,
	linux-arch@...r.kernel.org, vincent.guittot@...aro.org,
	xiaoguangrong@...ux.vnet.ibm.com, wangyun@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	rusty@...tcorp.com.au, namhyung@...nel.org, tglx@...utronix.de,
	laijs@...fujitsu.com, zhong@...ux.vnet.ibm.com,
	netdev@...r.kernel.org, oleg@...hat.com, sbw@....edu,
	tj@...nel.org, akpm@...ux-foundation.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 15/45] rcu: Use get/put_online_cpus_atomic() to
 prevent CPU offline

On Wed, 2013-06-26 at 07:34 -0700, Paul E. McKenney wrote:
> On Wed, Jun 26, 2013 at 03:29:40PM +0100, David Laight wrote:
> > > Once stop_machine() is gone from the CPU offline path, we won't be able
> > > to depend on disabling preemption to prevent CPUs from going offline
> > > from under us.
> > 
> > Could you use an rcu-like sequence so that disabling pre-emption
> > would be enough?
> > 
> > Something like rebuilding the cpu list, then forcing yourself
> > to run on all the cpu.
> > 
> > That would be far less intrusive.
> 
> It would also increase the latency of CPU-hotunplug operations.
> 

Is that a big deal?

-- Steve


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