linux-kernel - Re: [PATCH 4/9] sched: Move SCHED

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Message-ID: <87blaqnzho.mognet@arm.com>
Date:   Wed, 07 Apr 2021 11:46:43 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
        mgorman@...e.de, juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        bristot@...hat.com, joshdon@...gle.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org, greg@...ah.com
Subject: Re: [PATCH 4/9] sched: Move SCHED_DEBUG to debugfs

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.