Re: [PATCH sched_ext/for-7.1] sched_ext: Guard cpu_smt_mask() with CONFIG_SCHED_SMT

[Cheng-Yang Chou]

Hi Andrea,

On Sun, Mar 22, 2026 at 07:51:46AM +0100, Andrea Righi wrote:
> Wrap cpu_smt_mask() usage with CONFIG_SCHED_SMT to avoid build failures
> on kernels built without SMT support.
> 
> Fixes: 2197cecdb02c ("sched_ext: idle: Prioritize idle SMT sibling")
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-kbuild-all/202603221422.XIueJOE9-lkp@xxxxxxxxx/
> Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>
> ---
>  kernel/sched/ext_idle.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
> index d9596427b5aa1..857d8e902b448 100644
> --- a/kernel/sched/ext_idle.c
> +++ b/kernel/sched/ext_idle.c
> @@ -622,6 +622,7 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
>  		goto out_unlock;
>  	}
>  
> +#ifdef CONFIG_SCHED_SMT
>  	/*
>  	 * Use @prev_cpu's sibling if it's idle.
>  	 */
> @@ -633,6 +634,7 @@ s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
>  				goto out_unlock;
>  		}
>  	}
> +#endif
>  
>  	/*
>  	 * Search for any idle CPU in the same LLC domain.
> -- 
> 2.53.0
> 

Tested with the robot's config and the error is gone.

Reviewed-by: Cheng-Yang Chou <yphbchou0911@xxxxxxxxx>

-- 
Thanks,
Cheng-Yang