Re: [PATCH v10 2/7] x86, acpi, cpu-hotplug: Enable acpi to register all possible cpus at boot time.

[Dou Liyang]

Hi tglx,

å 2016å07æ29æ 21:36, Thomas Gleixner åé:
> On Tue, 26 Jul 2016, Dou Liyang wrote:
>
> > 1. Enable apic registeration flow to handle both enabled and disabled cpus.
> >    This is done by introducing an extra parameter to generic_processor_info to
> >    let the caller control if disabled cpus are ignored.
>
> If I'm reading the patch correctly then the 'enabled' argument controls more
> than the disabled cpus accounting. It also controls the modification of
> num_processors and the present mask.

In the patch, they both need mapping to a logic cpu.
As you said, the 'enabled' controls extra functions:

1. num_processors parameter
2. physid_set method
3. set_cpu_present method

> > -int generic_processor_info(int apicid, int version)
> > +static int __generic_processor_info(int apicid, int version, bool enabled)
> >  {
> >  	int cpu, max = nr_cpu_ids;
> >  	bool boot_cpu_detected = physid_isset(boot_cpu_physical_apicid,
> > @@ -2032,7 +2032,8 @@ int generic_processor_info(int apicid, int version)
> >  			   " Processor %d/0x%x ignored.\n",
> >  			   thiscpu, apicid);
> >
> > -		disabled_cpus++;
> > +		if (enabled)
> > +			disabled_cpus++;
> >  		return -ENODEV;
> >  	}
> >
> > @@ -2049,7 +2050,8 @@ int generic_processor_info(int apicid, int version)
> >  			" reached. Keeping one slot for boot cpu."
> >  			"  Processor %d/0x%x ignored.\n", max, thiscpu, apicid);
> >
> > -		disabled_cpus++;
> > +		if (enabled)
> > +			disabled_cpus++;
>
> This is utterly confusing. That code path cannot be reached when enabled is
> false, because num_processors is 0 as we never increment it when enabled is
> false.
>
> That said, I really do not like this 'slap some argument on it and make it
> work somehow' approach.
>
> The proper solution for this is to seperate out the functionality which you
> need for the preparation run (enabled = false) and make sure that the
> information you need for the real run (enabled = true) is properly cached
> somewhere so we don't have to evaluate the same thing over and over.

Thank you very much for your advice. That solution is very good for me.

I thought about the differences between them carefully. Firstly, I
intend to separate out the functionality in two functions. It's simple
but not good. Then, I try to put them together to judge just once.

After, considering the judgment statement independence and the order of
assignment. I remove all the "if (enabled)" code and do the unified
judgment like this:

@@ -2180,12 +2176,19 @@ int __generic_processor_info(int apicid, int
version, bool enabled)
                apic->x86_32_early_logical_apicid(cpu);
 #endif
        set_cpu_possible(cpu, true);
-       if (enabled)
+
+       if (enabled){
+               num_processors++;
+               physid_set(apicid, phys_cpu_present_map);
                set_cpu_present(cpu, true);
+       }else{
+               disabled_cpus++;
+       }

        return cpu;
 }

I hope that patch could consistent with your advice. And I will submit
the detailed modification in the next version patches.

Thanks,

Dou.