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

[Chenhui Zhao]

On Thu, Aug 6, 2015 at 11:16 AM, Scott Wood <scottwood@xxxxxxxxxxxxx> 
wrote:
> On Wed, 2015-08-05 at 19:08 +0800, Chenhui Zhao wrote:
> >  On Sat, Aug 1, 2015 at 8:22 AM, Scott Wood <scottwood@xxxxxxxxxxxxx>
> >  wrote:
> >  > On Fri, 2015-07-31 at 17:20 +0800,  b29983@xxxxxxxxxxxxxxxxxx:
> >  > >  +             /*
> >  > >  +              * 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

Remapping is a concise solution. what's the harm of it?
Keeping things simple is good in my opinion.

-Chenhui



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