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

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Message-ID: <50112647.1020206@linux.vnet.ibm.com>
Date:	Thu, 26 Jul 2012 16:43:11 +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
Subject: Re: [RFC PATCH 0/6] CPU hotplug: Reverse invocation of notifiers
 during CPU hotplug

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

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