linux-kernel - Re: [PATCH 3/3] PowerPC/mpc85xx: Add hotplug support on E6500 cores

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Date:	Wed, 5 Aug 2015 22:16:44 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Chenhui Zhao <chenhui.zhao@...escale.com>
CC:	<b29983@...escale.com>, <b07421@...escale.com>,
	<linux-kernel@...r.kernel.org>,
	Tang Yuantian <Yuantian.Tang@...escale.com>,
	Tang Yuantian <Yuantian.Tang@...scale.com>
Subject: Re: [PATCH 3/3] PowerPC/mpc85xx: Add hotplug support on E6500 cores

On Wed, 2015-08-05 at 19:08 +0800, Chenhui Zhao wrote:
> On Sat, Aug 1, 2015 at 8:22 AM, Scott Wood <scottwood@...escale.com> 
> wrote:
> > On Fri, 2015-07-31 at 17:20 +0800,  b29983@...escale.comwrote:
> > >  +             /*
> > >  +              * If both threads are offline, reset core to start.
> > >  +              * When core is up, Thread 0 always gets up first,
> > >  +              * so bind the current logical cpu with Thread 0.
> > >  +              */
> > >  +             if (hw_cpu != cpu_first_thread_sibling(hw_cpu)) {
> > >  +                     int hw_cpu1, hw_cpu2;
> > >  +
> > >  +                     hw_cpu1 = get_hard_smp_processor_id(primary);
> > >  +                     hw_cpu2 = get_hard_smp_processor_id(primary + 
> > > 1);
> > >  +                     set_hard_smp_processor_id(primary, hw_cpu2);
> > >  +                     set_hard_smp_processor_id(primary + 1, 
> > > hw_cpu1);
> > >  +                     /* get new physical cpu id */
> > >  +                     hw_cpu = get_hard_smp_processor_id(nr);
> > 
> > NACK as discussed in http://patchwork.ozlabs.org/patch/454944/
> > 
> > -Scott
> 
> You said,
> 
>     There's no need for this. I have booting from a thread1, and having 
> it
>     kick its thread0, working locally without messing with the hwid/cpu
>     mapping.
> 
> I still have questions here. After a core reset, how can you boot 
> Thread1
> of the core first. As I know, Thread0 boots up first by default.

So the issue isn't that thread1 comes up first, but that you *want* thread1 
to come up first and it won't.  I don't think this remapping is an acceptable 
answer, though.  Instead, if you need only thread1 to come up, start the 
core, have thread0 start thread1, and then send thread0 into whatever waiting 
state it would be in if thread1 had never been offlined.

-Scott

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