linux-kernel - Re: [PATCH v7 29/31] fs/resctrl: Provide interface to create architecture specific debugfs area

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Message-ID: <d286d455-dbd7-49f0-acc2-7d5eb3b5c4e1@intel.com>
Date: Fri, 25 Jul 2025 16:55:26 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghuay@...dia.com>, "Maciej
 Wieczor-Retman" <maciej.wieczor-retman@...el.com>, Peter Newman
	<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
	<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
	<Dave.Martin@....com>, Chen Yu <yu.c.chen@...el.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v7 29/31] fs/resctrl: Provide interface to create
 architecture specific debugfs area

Hi Tony,

On 7/11/25 4:53 PM, Tony Luck wrote:
> Architectures are constrained to just the file interfaces provided by
> the file system for each resource. This does not allow for architecture
> specific debug interfaces.

(squashed context and problem description)

> 
> Add resctrl_debugfs_mon_info_arch_mkdir() which creates a directory in the
> debugfs file system for a resource. Naming follows the layout of the
> main resctrl hierarchy:
> 
> 	/sys/kernel/debug/resctrl/info/{resource}_MON/{arch}
> 
> The {arch} last level directory name matches the output of
> the user level "uname -m" command.
> 
> Architecture code may use this directory for debug information,
> or for minor tuning of features. It must not be used for basic
> feature enabling as debugfs may not be configured/mounted on
> production systems.
> 
> Suggested-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  include/linux/resctrl.h |  9 +++++++++
>  fs/resctrl/rdtgroup.c   | 29 +++++++++++++++++++++++++++++
>  2 files changed, 38 insertions(+)
> 
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 74cd2979549b..ed5085eeee1b 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -571,6 +571,15 @@ void resctrl_arch_reset_all_ctrls(struct rdt_resource *r);
>  extern unsigned int resctrl_rmid_realloc_threshold;
>  extern unsigned int resctrl_rmid_realloc_limit;
>  
> +/**
> + * resctrl_debugfs_mon_info_arch_mkdir() - Create a debugfs info directory.
> + *					   Removed by resctrl_exit().
> + * @r:	Resource (must be mon_capable).
> + *
> + * Return: dentry pointer on success, or NULL on error.
> + */
> +struct dentry *resctrl_debugfs_mon_info_arch_mkdir(struct rdt_resource *r);
> +
>  int resctrl_init(void);
>  void resctrl_exit(void);
>  
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index 9e667d3a93ae..fdd6cf372d6c 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -24,6 +24,7 @@
>  #include <linux/sched/task.h>
>  #include <linux/slab.h>
>  #include <linux/user_namespace.h>
> +#include <linux/utsname.h>
>  
>  #include <uapi/linux/magic.h>
>  
> @@ -4350,6 +4351,33 @@ int resctrl_init(void)
>  	return ret;
>  }
>  
> +static struct dentry *debugfs_resctrl_info;

Please move this declaration to be with its partner, debugfs_resctrl.

> +
> +/*
> + * Create /sys/kernel/debug/resctrl/info/{r->name}_MON/{arch} directory
> + * by request for architecture to use for debugging or minor tuning.
> + * Basic functionality of features must not be controlled by files
> + * added to this directory as debugs may not be configured/mounted

debugs -> debugfs

> + * on production systems.
> + */
> +struct dentry *resctrl_debugfs_mon_info_arch_mkdir(struct rdt_resource *r)
> +{
> +	struct dentry *moninfodir;
> +	char name[32];
> +
> +	if (!r->mon_capable)
> +		return NULL;
> +
> +	if (!debugfs_resctrl_info)
> +		debugfs_resctrl_info = debugfs_create_dir("info", debugfs_resctrl);
> +
> +	sprintf(name, "%s_MON", r->name);
> +
> +	moninfodir = debugfs_create_dir(name, debugfs_resctrl_info);
> +
> +	return debugfs_create_dir(utsname()->machine, moninfodir);
> +}
> +
>  static bool resctrl_online_domains_exist(void)
>  {
>  	struct rdt_resource *r;
> @@ -4401,6 +4429,7 @@ void resctrl_exit(void)
>  
>  	debugfs_remove_recursive(debugfs_resctrl);
>  	debugfs_resctrl = NULL;
> +	debugfs_resctrl_info = NULL;
>  	unregister_filesystem(&rdt_fs_type);
>  
>  	/*

Reinette