linux-kernel - Re: [PATCH 2/5] rseq: Move slice_ext

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Message-ID: <20260121154225-d38a4029-6ad9-4a83-926e-c83b6af49ac6@linutronix.de>
Date: Wed, 21 Jan 2026 15:50:55 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: tglx@...utronix.de, mathieu.desnoyers@...icios.com, 
	linux-kernel@...r.kernel.org, paulmck@...nel.org, boqun.feng@...il.com, corbet@....net, 
	prakash.sangappa@...cle.com, vineethr@...ux.ibm.com, kprateek.nayak@....com, 
	rostedt@...dmis.org, bigeasy@...utronix.de, arnd@...db.de, rdunlap@...radead.org, 
	rongevarg@...il.com, longman@...hat.com
Subject: Re: [PATCH 2/5] rseq: Move slice_ext_nsec to debugfs

On Wed, Jan 21, 2026 at 03:24:59PM +0100, Peter Zijlstra wrote:
> Move changing the slice ext duration to debugfs, a sliglty less permanent
> interface.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---

(...)

> --- a/kernel/rseq.c
> +++ b/kernel/rseq.c
> @@ -222,12 +222,16 @@ static const struct file_operations debu
>  	.release	= single_release,
>  };
>  
> +extern void rseq_slice_ext_init(struct dentry *root_dir);

This is actually a static function.

> +
>  static int __init rseq_debugfs_init(void)
>  {
>  	struct dentry *root_dir = debugfs_create_dir("rseq", NULL);
>  
>  	debugfs_create_file("debug", 0644, root_dir, NULL, &debug_ops);
>  	rseq_stats_init(root_dir);
> +	if (IS_ENABLED(CONFIG_RSEQ_SLICE_EXTENSIO))

Missing 'N' at the end.

> +		rseq_slice_ext_init(root_dir);
>  	return 0;
>  }
>  __initcall(rseq_debugfs_init);
> @@ -515,7 +519,9 @@ struct slice_timer {
>  	void		*cookie;
>  };

(...)

> +#ifdef CONFIG_DEBUG_FS

(...)

> +#else
> +static void rseq_slice_ext_init(struct dentry *root_dir) { }
> +#endif

It might be possible to just remove the CONFIG_DEBUG_FS ifdeffery and let the
compiler optimize away all of the debugfs-related code automatically.

(...)