Re: [PATCH 4/9] sched: Move SCHED_DEBUG to debugfs

[Valentin Schneider <valentin.schneider@arm.com>]

On 26/03/21 11:33, Peter Zijlstra wrote:
>  __read_mostly bool sched_debug_enabled;
>  
> +struct dentry *debugfs_sched;
> +
>  static __init int sched_init_debug(void)
>  {
> -	debugfs_create_file("sched_features", 0644, NULL, NULL,
> -			&sched_feat_fops);
> +	struct dentry __maybe_unused *numa;
> +
> +	debugfs_sched = debugfs_create_dir("sched", NULL);
> +
> +	debugfs_create_file("features", 0644, debugfs_sched, NULL, &sched_feat_fops);
> +	debugfs_create_bool("debug_enabled", 0644, debugfs_sched, &sched_debug_enabled);
> +

Could we kill this too? I'm probably biased because I've spent some amount
of time banging my head at topology problems, but this two-tiered debugging
setup (KCONFIG + cmdline or post-boot write) has always irked me.

I can't find the threads in a hurry, but ISTR justifications for keeping
this around were:
- Most distros have CONFIG_SCHED_DEBUG=y because knobs and ponies
- Topology debug prints are "too verbose"
- NUMA distance matrix processing gets slower

If we make it so distros stop / don't need to select CONFIG_SCHED_DEBUG,
then I don't think the above really stands anymore (also, sched_init_numa()
now has the same complexity regardless of sched_debug), and we could keep
everything under CONFIG_SCHED_DEBUG.