linux-kernel - Re: [PATCH] smp/hotplug: Move unparking of percpu threads to the control CPU

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Date:   Wed, 5 Jul 2017 11:17:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Vikram Mulukutla <markivx@...eaurora.org>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Sebastian Sewior <bigeasy@...utronix.de>
Subject: Re: [PATCH] smp/hotplug: Move unparking of percpu threads to the
 control CPU

On Wed, Jul 05, 2017 at 11:07:34AM +0200, Thomas Gleixner wrote:
> On Wed, 5 Jul 2017, Peter Zijlstra wrote:

> > OK, so if I get this right we do something like:
> > 
> > 
> > BP				AP
> > 
> > bringup_cpu();
> >   __cpu_up()  ------------>     /* stuff */
> >   bringup_wait_for_ap()
> >     wait_for_completion();
> > 				cpuhp_online_idle();
> > 		<------------    complete(&st->done);
> >     unpark()
> > 				while(1)
> > 				  do_idle();
> 
> actually I added after unpark():
> 
>      kick_ap()
>      wait_for_completion()
> 
> So the AP will execute the online callbacks in its own hotplug thread.

Indeed, but I stopped after the unpark() bits bcause well, that's what
you changed here :-)