[tip: x86/cache] fs/resctrl: Document that automatic counter assignment is best effort

[tip-bot2 for Ben Horgan]

The following commit has been merged into the x86/cache branch of tip:

Commit-ID:     9a1646211f8c67c7c98f8109607e3b962aea13eb
Gitweb:        https://git.kernel.org/tip/9a1646211f8c67c7c98f8109607e3b962aea13eb
Author:        Ben Horgan <ben.horgan@xxxxxxx>
AuthorDate:    Wed, 06 May 2026 09:28:54 +01:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Fri, 08 May 2026 12:25:22 +02:00

fs/resctrl: Document that automatic counter assignment is best effort

When using automatic counter assignment it's useful for a user to know
which counters they can expect to be assigned on group creation.

Document that automatic counter assignment is best effort and how to
discover any assignment failures.

Suggested-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Signed-off-by: Ben Horgan <ben.horgan@xxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Babu Moger <babu.moger@xxxxxxx>
Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Tested-by: Babu Moger <babu.moger@xxxxxxx>
Link: https://lore.kernel.org/20260506082855.3694761-1-ben.horgan@xxxxxxx
---
 Documentation/filesystems/resctrl.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index 2898a51..b388e91 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -479,6 +479,12 @@ with the following files:
 	"1":
 		Auto assignment is enabled.
 
+	Automatic counter assignment is done with best effort. If auto
+	assignment is enabled but there are not enough available counters then
+	monitor group creation could succeed while one or more events belonging
+	to the group may not have a counter assigned in all domains. Consult
+	mbm_L3_assignments for counter assignment states of the new groups.
+
 	Example::
 
 	  # echo 0 > /sys/fs/resctrl/info/L3_MON/mbm_assign_on_mkdir