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Date: Thu, 26 Jul 2012 16:43:11 +0530
From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
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To: Thomas Gleixner <tglx@linutronix.de>
CC: Alan Stern <stern@rowland.harvard.edu>, mingo@kernel.org,
        peterz@infradead.org, rusty@rustcorp.com.au,
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        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 0/6] CPU hotplug: Reverse invocation of notifiers
 during CPU hotplug
References: <Pine.LNX.4.44L0.1207251054420.2008-100000@iolanthe.rowland.org> <50101733.4030205@linux.vnet.ibm.com> <alpine.LFD.2.02.1207251758340.32033@ionos> <50103955.9020301@linux.vnet.ibm.com> <alpine.LFD.2.02.1207261248130.32033@ionos>
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On 07/26/2012 04:25 PM, Thomas Gleixner wrote:
> On Wed, 25 Jul 2012, Srivatsa S. Bhat wrote:
>> On 07/25/2012 10:00 PM, Thomas Gleixner wrote:
>>> struct hotplug_event hotplug_events_bp[CPU_HOTPLUG_MAX_EVENTS];
>>> struct hotplug_event hotplug_events_ap[CPU_HOTPLUG_MAX_EVENTS];
>>>    
>>> The _bp one is the list of events which are executed on the active cpu
>>> and the _ap ones are those executed on the hotplugged cpu.
>>>
>>> The core code advances the events in sync steps, so both BP and AP can
>>> issue a stop on the process and cause a rollback.
>>
>> What exactly does "sync steps" mean in this context? Also, for the CPU
> 
> Sync step means, that both sides need to synchronize - not at every
> step, but at well defined synchronization points. You can't advance
> the AP to online state unless the BP has done the preparatory stuff
> already.
> 
>> offline event, the event could start off with both the BP and the AP being
>> the same CPU.. Does this design take care of that case?
> 
> Once the AP leaves the state where tasks can be freely scheduled on
> it, the take down thread migrates automagically. And that's one of the
> first things I'm trying to do so the first synchronization point is
> after that.
> 

Oh.. Ok.. Thanks for the explanation!

Regards,
Srivatsa S. Bhat