Re: [PATCH v4] powerpc/smp: Use nid as fallback for package_id

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

* Gautham R Shenoy <ego@linux.vnet.ibm.com> [2020-01-30 16:27:47]:

> On Wed, Jan 29, 2020 at 07:21:21PM +0530, Srikar Dronamraju wrote:
> 
> [..snip..]
> 
> > --- a/arch/powerpc/kernel/smp.c
> > +++ b/arch/powerpc/kernel/smp.c
> > @@ -1185,10 +1185,34 @@ static inline void add_cpu_to_smallcore_masks(int cpu)
> >  	}
> >  }
> > 
> > +int get_physical_package_id(int cpu)
> > +{
> > +	int ppid = cpu_to_chip_id(cpu);
> > +
> > +#ifdef CONFIG_PPC_SPLPAR
> > +	/*
> > +	 * If the platform is PowerNV or Guest on KVM, ibm,chip-id is
> > +	 * defined. Hence we would return the chip-id as the
> > +	 * get_physical_package_id.
> > +	 */
> > +	if (ppid == -1 && firmware_has_feature(FW_FEATURE_LPAR)) {
> > +		struct device_node *np = of_get_cpu_node(cpu, NULL);
> > +
> > +		if (np) {
> > +			ppid = of_node_to_nid(np);
> > +			of_node_put(np);
> > +		}
> > +	}
> > +#endif /* CONFIG_PPC_SPLPAR */
> > +
> > +	return ppid;
> > +}
> >  static void add_cpu_to_masks(int cpu)
> >  {
> >  	int first_thread = cpu_first_thread_sibling(cpu);
> > -	int chipid = cpu_to_chip_id(cpu);
> > +	int ppid = get_physical_package_id(cpu);
> >  	int i;
> > 
> >  	/*
> > @@ -1217,11 +1241,11 @@ static void add_cpu_to_masks(int cpu)
> >  	for_each_cpu(i, cpu_l2_cache_mask(cpu))
> >  		set_cpus_related(cpu, i, cpu_core_mask);
> > 
> > -	if (chipid == -1)
> > +	if (ppid == -1)
> >  		return;
> 
> Can get_physical_package_id() return -1 ?
> 

Yes, it can return -1,
1. A System doesnt have CONFIG_PPC_SPLPAR: cpu_to_chip_id() might return -1.
2. A System with CONFIG_PPC_SPLPAR: Still can return -1 for following cases.
	a. Not having firmware feature FW_FEATURE_LPAR
	b. If for some reason, of_get_cpu_node property is not present.

> > 
> >  	for_each_cpu(i, cpu_online_mask)
> > -		if (cpu_to_chip_id(i) == chipid)
> > +		if (get_physical_package_id(i) == ppid)
> >  			set_cpus_related(cpu, i, cpu_core_mask);
> >  }

-- 
Thanks and Regards
Srikar Dronamraju