Re: [PATCH 1/2] arm64: topology: Prefer PE0 on NVIDIA Olympus SMT cores

[Andrea Righi <arighi@nvidia.com>]

On Wed, Sep 09, 2026 at 05:19:08PM +0200, Dietmar Eggemann wrote:
> On 09.09.26 08:26, Andrea Righi wrote:
> 
> [...]
> 
> > +void __init arm64_init_sched_topology(void)
> > +{
> > +	if (!IS_ENABLED(CONFIG_SCHED_SMT))
> > +		return;
> > +
> > +	if ((read_cpuid_id() & MIDR_CPU_MODEL_MASK) != MIDR_NVIDIA_OLYMPUS)
> > +		return;
> > +
> > +	if (!topology_core_has_smt(smp_processor_id()))
> > +		return;
> > +
> > +	set_sched_topology(arm64_asym_smt_topology);
> > +	pr_info("Enabling PE0 SMT preference for NVIDIA Olympus\n");
> 
> I'm not really a big fan of using this arm64 setup for NVIDIA Olympus
> alone here.
> 
> > +}
> > +
> > +int arch_asym_cpu_priority(int cpu)
> > +{
> > +	return MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 0) == 0;
> > +}
> > +
> 
> This is done since it will only be called for NVIDIA Olympus since it's
> the only CPU model enabling this. I think it will work but it's still
> ugly :-)
> 
> [...]
> 

Agreed on both points. As mentioned in the other email, I'll coordinate with the
firmware team on a proper ABI for describing the PE0 preference. For the systems
with the current firmware, I don't have many ideas on how to enable this... a
special scheduler facility enabled via kernel boot option? Other ideas?

Thanks,
-Andrea