linux-kernel - Re: [PATCH] cpuhotplug: introduce try_get_online

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Message-ID: <20090608142520.GA6961@linux.vnet.ibm.com>
Date:	Mon, 8 Jun 2009 07:25:20 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>, dipankar@...ibm.com
Subject: Re: [PATCH] cpuhotplug: introduce try_get_online_cpus() take 2

On Mon, Jun 08, 2009 at 09:49:34AM +0530, Gautham R Shenoy wrote:
> Hi Paul,
> 
> On Fri, Jun 05, 2009 at 08:37:14AM -0700, Paul E. McKenney wrote:
> > 
> > One question for Gautham Shenoy -- are non-atomic CPU-hotplug notifiers
> > always invoked from the task that did the cpu_hotplug_begin()?
> 
> Except for the notifiers handling two events, rest of the notifiers
> are always invoked from the task that did the cpu_hotplug_begin().
> 
> The two events are CPU_DYING which is called from the context of the
> stop_machine_thread and CPU_STARTING which is called from the context of
> the idle thread on the CPU that has just come up. The notifiers handling
> these two events are expected to be atomic.
> 
> > If so, well and good.  If not, then it would not be possible to
> > expedite RCU grace periods from within CPU-hotplug notifiers.
> 
> I hope this would be good enough :-)

Works for me!!  ;-)

							Thanx, Paul
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