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

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Date:	Wed, 26 Jun 2013 10:29:48 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	paulmck@...ux.vnet.ibm.com, 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,
	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

Hello,

On Wed, Jun 26, 2013 at 11:33:43AM -0400, Steven Rostedt wrote:
> I thought the whole deal with this patchset was to remove stop_machine
> from CPU hotplug. Why halt all CPUs just to remove one? stomp_machine()
> is extremely intrusive for the entire system, where as one CPU making
> sure all CPUs schedule isn't very intrusive at all.
> 
> I didn't think the idea of this patch set was to make CPU hotplug
> faster, just less intrusive to the system.

Yeap, removal of stop_machine is a great improvement in itself.  ISTR
mentions of hot-unplug latency but I could be mistaken.  Srivatsa, can
you please chime in on that?

Thanks.

-- 
tejun
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