[PATCH v13 25/25] x86,fs/resctrl: Document telemetry mount timing caveat

[Tony Luck]

The PMT driver enumerates telemetry features asynchronously, so an
automatic mount of resctrl from /etc/fstab early in boot may occur before
those features are available, resulting in them not being enabled in the
mounted instance.

Add a footnote to the 'If telemetry monitoring is enabled' sentence
explaining the race and providing a solution.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
v13:
	Drop the "Mounting resctrl with telemetry" section. Include the
	solution in the footnote.
---
 Documentation/filesystems/resctrl.rst | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index b52795e03303..dcae1076f863 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -629,7 +629,7 @@ When monitoring is enabled all MON groups will also contain:
 	each instance of an L3 cache. Each directory contains files for the enabled
 	L3 events (e.g. "llc_occupancy", "mbm_total_bytes", and "mbm_local_bytes").
 
-	If telemetry monitoring is enabled, there will be a "mon_PERF_PKG_YY"
+	If telemetry monitoring is enabled [#]_, there will be a "mon_PERF_PKG_YY"
 	directory for each physical processor package. Each directory contains
 	files for the enabled telemetry events (e.g. "core_energy". "activity",
 	"uops_retired", etc.)
@@ -668,6 +668,11 @@ When monitoring is enabled all MON groups will also contain:
 	returned if the MBM event does not have an assigned counter in the
 	CTRL_MON group nor in any of its associated MON groups.
 
+.. [#] Telemetry features are enumerated asynchronously by the PMT driver, so
+   an automatic mount of resctrl from ``/etc/fstab`` at boot may not enable
+   them. To avoid this race, defer the mount until after the ``pmt_telemetry``
+   module has loaded.
+
 "mon_hw_id":
 	Available only with debug option. The identifier used by hardware
 	for the monitor group. On x86 this is the RMID.
-- 
2.55.0