Re: [PATCH v5 27/29] fs/resctrl: Add file system mechanism for architecture info file

[Luck, Tony]

On Fri, Jun 06, 2025 at 09:26:06AM -0700, Reinette Chatre wrote:
> With /sys/kernel/debug/resctrl potentially mirroring /sys/fs/resctrl to
> support various debugging scenarios there may later be resource level
> debugging for which a "/sys/kernel/debug/resctrl/info/<resource>/<debugfile>" can
> be used. Considering this it looks to me as though one possible boundary could
> be to isolate arch specific debug to, for example, a new directory named
> "/sys/kernel/debug/resctrl/info/arch_debug_name_tbd/". By placing the
> arch debug in a sub-directory named "info" it avoids collision with resource
> group names with naming that also avoids collision with resource names since
> all these names are controlled by resctrl fs. 


That seems like a good path. PoC patch below. Note that I put the dentry
for the debug info directory into struct rdt_resource. So no call from
architecture to file system code needed to access.

Directory layout looks like this:

# tree /sys/kernel/debug/resctrl/
/sys/kernel/debug/resctrl/
└── info
    ├── L2
    ├── L3
    ├── MB
    └── SMBA

6 directories, 0 files

-Tony

---

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 5e28e81b35f6..78dd0f8f7ad8 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -281,6 +281,7 @@ enum resctrl_schema_fmt {
  * @mbm_cfg_mask:	Bandwidth sources that can be tracked when bandwidth
  *			monitoring events can be configured.
  * @cdp_capable:	Is the CDP feature available on this resource
+ * @arch_debug_info:	Debugfs info directory for architecture use
  */
 struct rdt_resource {
 	int			rid;
@@ -297,6 +298,7 @@ struct rdt_resource {
 	enum resctrl_schema_fmt	schema_fmt;
 	unsigned int		mbm_cfg_mask;
 	bool			cdp_capable;
+	struct dentry		*arch_debug_info;
 };
 
 /*
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index ed4fc45da346..48c587201fb6 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -4274,6 +4274,8 @@ void resctrl_offline_cpu(unsigned int cpu)
  */
 int resctrl_init(void)
 {
+	struct dentry *debuginfodir;
+	struct rdt_resource *r;
 	int ret = 0;
 
 	seq_buf_init(&last_cmd_status, last_cmd_status_buf,
@@ -4320,6 +4322,12 @@ int resctrl_init(void)
 	 */
 	debugfs_resctrl = debugfs_create_dir("resctrl", NULL);
 
+	/* Create debug info directories for each resource */
+	debuginfodir = debugfs_create_dir("info", debugfs_resctrl);
+
+	for_each_rdt_resource(r)
+		r->arch_debug_info = debugfs_create_dir(r->name, debuginfodir);
+
 	return 0;
 
 cleanup_mountpoint: