linux-kernel - Re: [RFC PATCH 0/6] CPU hotplug: Reverse invocation of notifiers during CPU hotplug

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Message-ID: <501125D3.9050705@linux.vnet.ibm.com>
Date:	Thu, 26 Jul 2012 16:41:15 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Alan Stern <stern@...land.harvard.edu>, mingo@...nel.org,
	peterz@...radead.org, rusty@...tcorp.com.au,
	paulmck@...ux.vnet.ibm.com, namhyung@...nel.org, tj@...nel.org,
	rjw@...k.pl, nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC PATCH 0/6] CPU hotplug: Reverse invocation of notifiers
 during CPU hotplug

On 07/26/2012 04:32 PM, Thomas Gleixner wrote:
> On Wed, 25 Jul 2012, Srivatsa S. Bhat wrote:
>> On 07/25/2012 10:00 PM, Thomas Gleixner wrote:
>>> While I thought about having a full dependency tracking system, I'm
>>> quite convinced by now, that hotplug is a rather linear sequence which
>>> does not provide much room for paralell setup/teardown.
>>>
>>
>> Pretty much, when considering hotplug of a single CPU.
>>
>> (But when considering booting, Arjan had proposed (while discussing
>> about his asynchronous booting patch) that it would be good to split
>> up physical vs logical parts of the booting/hotplug, so that the
>> physical part can happen in parallel with other CPUs, while the
>> logical online can be done serially, much later. Anyway, this is
>> slightly off-topic here, since we are mainly talking about hotplug
>> of a single cpu here. I just thought of putting a word about that
>> here, since we are discussing hotplug redesign anyways..)
> 
> Well, the nice thing about having a proper state machine is that you
> can tell the code to advance the BP only to the "kick the other cpu"
> step, which is before the first sync point, so you can leave the state
> there and continue with "bring it fully online" later. 
> 
> So that feature comes basically for free. :)
> 

Ah! Nice :-)

Regards,
Srivatsa S. Bhat

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