[RFC PATCH v2 19/19] Documentation: arm64: mpam: Describe the L2 monitor events

[Jinjie Ruan]

resctrl can now monitor at the L2 scope, so MPAM exposes the CSU and
MBWU counters of an L2 group as l2c_occupancy and mbm_core_bytes.

Update the list of supported features. Say why a bandwidth counter is
assigned for the life of the monitoring group: rewriting its filter
restarts the count.

Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
---
 Documentation/arch/arm64/mpam.rst     | 23 ++++++++++++++---------
 Documentation/filesystems/resctrl.rst |  6 ++++++
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/Documentation/arch/arm64/mpam.rst b/Documentation/arch/arm64/mpam.rst
index e445f4078ee1..9c0a08ef74bf 100644
--- a/Documentation/arch/arm64/mpam.rst
+++ b/Documentation/arch/arm64/mpam.rst
@@ -32,8 +32,9 @@ Because the user interface to MPAM is via resctrl, only MPAM features that are
 compatible with resctrl can be exposed to user-space.
 
 MSC are considered as a group based on the topology. MSC that correspond with
-the L3 cache are considered together, it is not possible to mix MSC between L2
-and L3 to 'cover' a resctrl schema.
+the L3 cache are considered together, as are MSC that correspond with the L2
+cache; it is not possible to mix MSC between L2 and L3 to 'cover' a resctrl
+schema.
 
 The supported features are:
 
@@ -61,9 +62,11 @@ The supported features are:
   When the MPAM driver finds multiple groups of MSC it can use for the 'MB'
   schema, it prefers the group closest to the L3 cache.
 
-* Cache Storage Usage (CSU) counters can expose the 'llc_occupancy' provided
-  there is at least one CSU monitor on each MSC that makes up the L3 group.
-  Exposing CSU counters from other caches or devices is not supported.
+* Cache Storage Usage (CSU) counters expose the occupancy of the cache they
+  monitor: 'llc_occupancy' for the L3 group and 'l2c_occupancy' for the L2
+  group, provided there is at least one CSU monitor on each MSC that makes up
+  the group. Exposing CSU counters from other caches or devices is not
+  supported.
 
 * Memory Bandwidth Usage (MBWU) on or after the L3 cache.  resctrl uses the
   L3 cache-id to identify where the memory bandwidth is measured. For this
@@ -82,10 +85,12 @@ The supported features are:
   have a corresponding L3 cache. 'mbm_local_bytes' is not exposed as MPAM
   cannot distinguish local traffic from global traffic.
 
-  All these restrictions based on L3 cache are due to resctrl, currently, only
-  supporting monitoring at the L3 scope. It is expected that going forward more
-  MBWU monitors can be exposed to the user after support for more monitoring
-  scopes is added to resctrl.
+  MBWU monitors on an L2 MSC expose the bandwidth the cache sees as the
+  'mbm_core_bytes' event on the L2 resource.
+
+  These restrictions are due to resctrl only supporting monitoring at the L2
+  and L3 cache scopes. MBWU monitors on caches at other levels, or on devices,
+  are not exposed.
 
 Command line parameters
 =======================
diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index b52795e03303..c07d8f7223ff 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -495,6 +495,12 @@ with the following files:
 		bytes) at which a previously used LLC_occupancy
 		counter can be considered for reuse.
 
+If monitoring is available at other cache levels there will be a
+"<LEVEL>_MON" directory for each of them, with the same "num_rmids" and
+"mon_features" files. For example an L2 cache exposes "l2c_occupancy" and
+"mbm_core_bytes" in "L2_MON". The counter assignment interface
+("mbm_assign_mode", "mbm_L3_assignments") is specific to the L3.
+
 If telemetry monitoring is available there will be a "PERF_PKG_MON" directory
 with the following files:
 
-- 
2.34.1