Re: [PATCH v2 sched_ext/for-7.1] tools/sched_ext: Add compat handling for sub-scheduler ops

[Cheng-Yang Chou]

Hi Andrea,

On Sun, Mar 22, 2026 at 07:35:46AM +0100, Andrea Righi wrote:
> Extend SCX_OPS_OPEN() with compatibility handling for ops.sub_attach()
> and ops.sub_detach(), allowing scx C schedulers with sub-scheduler
> support to run on kernels both with and without its support.
> 
> Cc: Cheng-Yang Chou <yphbchou0911@xxxxxxxxx>
> Fixes: ebeca1f930ea ("sched_ext: Introduce cgroup sub-sched support")
> Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>
> ---
> Changes in v2:
>  - Handle sub_cgroup_id in older kernels (Cheng-Yang Chou)
>  - Link to v1: https://lore.kernel.org/all/20260321102036.58734-1-arighi@xxxxxxxxxx
> 
>  tools/sched_ext/include/scx/compat.h | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/tools/sched_ext/include/scx/compat.h b/tools/sched_ext/include/scx/compat.h
> index 9e0c8f3161e87..039854c490d5e 100644
> --- a/tools/sched_ext/include/scx/compat.h
> +++ b/tools/sched_ext/include/scx/compat.h
> @@ -160,6 +160,7 @@ static inline long scx_hotplug_seq(void)
>   * COMPAT:
>   * - v6.17: ops.cgroup_set_bandwidth()
>   * - v6.19: ops.cgroup_set_idle()
> + * - v7.1:  ops.sub_attach(), ops.sub_detach(), ops.sub_cgroup_id
>   */
>  #define SCX_OPS_OPEN(__ops_name, __scx_name) ({					\
>  	struct __scx_name *__skel;						\
> @@ -181,6 +182,21 @@ static inline long scx_hotplug_seq(void)
>  		fprintf(stderr, "WARNING: kernel doesn't support ops.cgroup_set_idle()\n"); \
>  		__skel->struct_ops.__ops_name->cgroup_set_idle = NULL;	\
>  	}									\
> +	if (__skel->struct_ops.__ops_name->sub_attach &&			\
> +	    !__COMPAT_struct_has_field("sched_ext_ops", "sub_attach")) {	\
> +		fprintf(stderr, "WARNING: kernel doesn't support ops.sub_attach()\n"); \
> +		__skel->struct_ops.__ops_name->sub_attach = NULL;		\
> +	}									\
> +	if (__skel->struct_ops.__ops_name->sub_detach &&			\
> +	    !__COMPAT_struct_has_field("sched_ext_ops", "sub_detach")) {	\
> +		fprintf(stderr, "WARNING: kernel doesn't support ops.sub_detach()\n"); \
> +		__skel->struct_ops.__ops_name->sub_detach = NULL;		\
> +	}									\
> +	if (__skel->struct_ops.__ops_name->sub_cgroup_id > 0 &&		\
> +	    !__COMPAT_struct_has_field("sched_ext_ops", "sub_cgroup_id")) { \
> +		fprintf(stderr, "WARNING: kernel doesn't support ops.sub_cgroup_id\n"); \
> +		__skel->struct_ops.__ops_name->sub_cgroup_id = 0;		\
> +	}									\
>  	__skel; 								\
>  })
>  
> -- 
> 2.53.0
> 

Looks good!

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

-- 
Thanks,
Cheng-Yang