Re: [PATCH v7 4/8] powerpc/smp: Introduce CONFIG_SCHED_MC to guard MC scheduling bits

[K Prateek Nayak <kprateek.nayak@amd.com>]

(Trimming the cc to kernel/sched/ folks)

On 8/26/2025 2:57 PM, Shrikanth Hegde wrote:
> 
> 
> On 8/26/25 9:43 AM, K Prateek Nayak wrote:
>> PowerPC enables the MC scheduling domain by default on systems with
>> coregroup support without having a SCHED_MC config in Kconfig.
>>
>> The scheduler uses CONFIG_SCHED_MC to introduce the MC domain in the
>> default topology (core) and to optimize the default CPU selection
>> routine (sched-ext).
> 
> Curious to know if sched_ext usage. i see below code.
> 
> if (static_branch_maybe(CONFIG_SCHED_MC, &scx_selcpu_topo_llc))
> 
> scx_selcpu_topo_llc = true if there is sd_llc. One can have llc domain without MC domain.
> I am wondering whats the reason behind the clubbing.

Seems to be an artifact carried forward since commit dfa4ed29b18c
("sched_ext: Introduce LLC awareness to the default idle selection
policy")

The commit 860a45219bce ("sched_ext: Introduce NUMA awareness to the
default idle selection policy") continued to build on top of that except
that it was fine to put the NUMA bits behind CONFIG_NUMA check since
topology.c only adds SD_NUMA under those circumstances but sd_llc is
just the highest SD_SHARE_LLC domain and shouldn't really depend on
CONFIG_SCHED_MC.

The ext part already has a check for llc_numa_mismatch() to only
enable "scx_selcpu_topo_numa" when llc and NUMA boundaries don't
overlap so I think that dependency on CONFIG_SCHED_MC can be safely
removed.

-- 
Thanks and Regards,
Prateek