Re: [Xen-devel] [PATCH v3 04/11] x86/intel_pstate: relocate the driver register function

["Wang, Wei W" <wei.w.wang@xxxxxxxxx>]

On 18/06/2015 22:30, Jan Beulich wrote:
> >>> On 11.06.15 at 10:27, <wei.w.wang@xxxxxxxxx> wrote:
> > Register the CPU hotplug notifier when the driver is registered, and
> > move the driver register function to the cpufreq.c.
> 
> The first half of the sentence fails to say why. And I suppose if you 
> explained
> that (to yourself) you'd figure that the change is wrong (or at least altering
> behavior in a way that needs more explanation to be verifiably correct): The
> calls to cpufreq_register_driver() sit in __initcall handlers, yet what you
> replace is a presmp_initcall. I.e. all APs being brought up at boot time won't
> get the callback invoked for them anymore.
> 
> I suppose you tested your series on a system where the new driver will kick
> in. You of course also need to test the case where this isn't the case -
> everything needs to continue to function there.

The cpu_callback() is removed in the following patch (05/11) because it's 
redundant.
Functions in cpufreq_register_driver() are also called only once, because other 
calls to cpufreq_register_driver() will just return due to the unsuccessful 
condition check at the beginning of the function.

> 
> > --- a/xen/drivers/cpufreq/cpufreq.c
> > +++ b/xen/drivers/cpufreq/cpufreq.c
> > @@ -630,12 +630,21 @@ static struct notifier_block cpu_nfb = {
> >      .notifier_call = cpu_callback
> >  };
> >
> > -static int __init cpufreq_presmp_init(void)
> > +int cpufreq_register_driver(struct cpufreq_driver *driver_data)
> >  {
> >      void *cpu = (void *)(long)smp_processor_id();
> >      cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
> > +    if (!driver_data || !driver_data->init
> > +        || !driver_data->verify || !driver_data->exit
> > +        || (!driver_data->target == !driver_data->setpolicy))
> 
> Do you really want/need to enforce this policy (target set if and only if
> setpolicy is not set) here? And if that's to uniformly hold, the two could be
> put into a union...

driver_data->target() is used by a driver which relies on the old Governor 
framework.
driver_data->setpolicy() is used by a driver which implements its internal 
governor.
So, the driver either uses the old Governor framework or has its own private 
internal governor.
We shouldn't change to use union, because in many places, we distinguish the 
two by checking if it's using "->target" or "->setpolicy".

Best,
Wei

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