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

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Message-ID: <20090608041934.GB17979@in.ibm.com>
Date:	Mon, 8 Jun 2009 09:49:34 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.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

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 :-)
> 
> 							Thanx, Paul
> 

-- 
Thanks and Regards
gautham
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