Re: [PATCH v2 3/3] sched/fair: Add compile time check in fastpaths for CONFIG_SCHED_SMT=n

[Phil Auld <pauld@redhat.com>]

Hi Shrikanth,

On Tue, May 12, 2026 at 08:51:25PM +0530 Shrikanth Hegde wrote:
> For fastpaths such as wakeup, load balance even a minimal code additons
> can pop up. Add IS_ENABLED checks there to ensure there is no overhead.

"For fastpaths such as wakeup and load balance, even minimal code additions
can add up. Add IS_ENABLED() checks..."  ?

> 
> Other places are either have sched_smt_active() check or they are not in

s/are//

"have a sched_smt_active_check()" or drop "check" ? 


Otherwise lgtm.

Reviewed-by: Phil Auld <pauld@redhat.com>


Cheers,
Phil



> fast paths.
> 
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
>  kernel/sched/fair.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 353e31ecaadc..b6f9592b31fd 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1586,6 +1586,9 @@ static inline bool is_core_idle(int cpu)
>  {
>  	int sibling;
>  
> +	if (!IS_ENABLED(CONFIG_SCHED_SMT))
> +		return true;
> +
>  	for_each_cpu(sibling, cpu_smt_mask(cpu)) {
>  		if (cpu == sibling)
>  			continue;
> @@ -12003,7 +12006,8 @@ static int should_we_balance(struct lb_env *env)
>  			 * idle has been found, then its not needed to check other
>  			 * SMT siblings for idleness:
>  			 */
> -			cpumask_andnot(swb_cpus, swb_cpus, cpu_smt_mask(cpu));
> +			if (IS_ENABLED(CONFIG_SCHED_SMT))
> +				cpumask_andnot(swb_cpus, swb_cpus, cpu_smt_mask(cpu));
>  			continue;
>  		}
>  
> -- 
> 2.47.3
> 
> 

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