Re: [PATCH v2 0/3] sched: Simplify ifdeffery around CONFIG_SCHED_SMT

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

Hello Shrikanth,

On 5/12/2026 8:51 PM, Shrikanth Hegde wrote:
> Semantics
> =========
> - For CONFIG_SCHED_SMT=y:
>     No functional change.
> - For CONFIG_SCHED_SMT=n:
>     - cpu_smt_mask(cpu) becomes cpumask_of(cpu), effectively making it
>       per CPU with no siblings.
>     - sched_smt_present remains defined, but never becomes active:
>     	 Since cpumask_weight(cpumask_of(cpu)) == 1
> 
> Performance impact
> ==================
> - CONFIG_SCHED_SMT=y:
>     No change in generated code.
> - CONFIG_SCHED_SMT=n:
>     - Small increase in text size (~0.01%) due to removal of compile-time
>       stubs. Most paths remain effectively dead due to static keys.
>     - Fast paths are protected using IS_ENABLED(CONFIG_SCHED_SMT).
> 
> With that, cpu_smt_mask() to be used unconditionally and reduces
> CONFIG_SCHED_SMT-specific code paths, improving readability and
> maintainability.
> 
> This leaves the remaining use of CONFIG_SCHED_SMT mainly for topology
> handling bits.

Thank you again cleaning this up! Feel free to include:

Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>

I also tested removing the "select SCHED_SMT" dependency for x86 after
guarding SDTL_INIT(..., SMT) behind CONFIG_SCHED_SMT and the system is
up fine; performance is terrible as expected :-)

-- 
Thanks and Regards,
Prateek