config-linux: add intelRdt.enableMonitoring (#1287)

Add a parameter for enabling per-container resctrl monitoring.

This supersedes and replaces the previous "enableCMT" and "enableMBM"
settings whose functionality was very vaguely specified. Separate
parameter for every monitoring metric does not seem to make much sense, in
particular because in the resctrl filesystem it is not possible to
selectively enable a subset of the monitoring features. You always get
all the metrics that the system provides. Also, with separate settings
(and corresponding check if the specific metric is available) the user
cannot specify "enable whatever is available" - setting everything to
"true" might fail because one of the metrics is not available on the
platform. In addition, having separate parameters is very
future-unproof, making support for new monitoring metrics unnecessarily
cumbersome to add. New metrics are certain to be added in new hardware
generations, e.g. perf/energy monitoring in the near future
(https://lkml.org/lkml/2025/5/21/1631), and requiring an update to the
runtime-spec for each one of them feels like an overkill without much
benefits. It is easier to have one switch for "enable container-specific
metrics" and let the user read whatever metrics the platform provides.

Moreover, it is not even possible to turn off monitoring (from the
resctrl filesystem). For example, you always get the metrics for all
CTRL_MON groups (closIDs). However, that is not always very useful as
there likely are a lot of applications packed in the same group. The new
intelRdt.enableMontoring parameter will enable creation of a MON group
specific to a single container allowing monitoring of resctrl metrics on
per-container granularity.

Signed-off-by: Markus Lehtonen <[email protected]>

Author: marquiz

config-linux.md

@@ -748,6 +748,7 @@ The following parameters can be specified for the container:
 * **`memBwSchema`** *(string, OPTIONAL)* - specifies the schema of memory bandwidth per L3 cache id.
     The value MUST start with `MB:` and MUST NOT contain newlines.
 * **`schemata`** *(array of strings, OPTIONAL)* - specifies the schemata to be written to the `schemata` file in resctrlfs. Each element represents one line in the `schemata` file. The value MUST NOT contain newlines.
+* **`enableMonitoring`** *(boolean, OPTIONAL)* - enables resctrl monitoring for the container.
 
 The following rules on parameters MUST be applied:
 
@@ -769,13 +770,20 @@ The following rules on parameters MUST be applied:
 
 * If `closID` is set, and none of `l3CacheSchema`, `memBwSchema` or `schemata` are set, runtime MUST check if corresponding pre-configured directory `closID` is present in mounted `resctrl`. If such pre-configured directory `closID` exists, runtime MUST assign container to this `closID` and [generate an error](runtime.md#errors) if directory does not exist.
 
-* **`enableCMT`** *(boolean, OPTIONAL)* - specifies if Intel RDT CMT should be enabled:
-    * CMT (Cache Monitoring Technology) supports monitoring of the last-level cache (LLC) occupancy
-      for the container.
-
-* **`enableMBM`** *(boolean, OPTIONAL)* - specifies if Intel RDT MBM should be enabled:
-    * MBM (Memory Bandwidth Monitoring) supports monitoring of total and local memory bandwidth
-      for the container.
+* If `enableMonitoring` is set, the runtime MUST create a dedicated MON group
+  for the container. The runtime MUST use the container ID from
+  [`start`](runtime.md#start) as the name of the MON group, i.e. create
+  `mon_groups/<container-id>/` subdirectory under the top-level CTRL_MON group
+  (named after `closID` or `<container-id>`, see above). The runtime MUST
+  delete the MON group after the container is deleted. If creation of the MON
+  group fails (e.g. the maximum number of MON groups is reached) the runtime MUST
+  return an error.
+
+> **NOTE:** The `enableCMT` and `enableMBM` parameters, available in runtime-spec versions v1.1.0 through v1.2.1, were
+> replaced with a unified `enableMonitoring` parameter in v1.3.0. Their semantics were loosely defined and there were
+> no known implementations. More critically, these parameters were problematic as hardware does not support selective
+> enabling of individual monitoring features. This scheme also made it unnecessarily complex to add support for new
+> monitoring features, without providing any recognized benefits.
 
 ### Example
 

schema/config-linux.json

@@ -278,10 +278,7 @@
                         "type": "string",
                         "pattern": "^MB:[^\\n]*$"
                     },
-                    "enableCMT": {
-                        "type": "boolean"
-                    },
-                    "enableMBM": {
+                    "enableMonitoring": {
                         "type": "boolean"
                     }
                 }

specs-go/config.go

@@ -855,13 +855,9 @@ type LinuxIntelRdt struct {
 	// NOTE: Should not be specified if Schemata is non-empty.
 	MemBwSchema string `json:"memBwSchema,omitempty"`
 
-	// EnableCMT is the flag to indicate if the Intel RDT CMT is enabled. CMT (Cache Monitoring Technology) supports monitoring of
-	// the last-level cache (LLC) occupancy for the container.
-	EnableCMT bool `json:"enableCMT,omitempty"`
-
-	// EnableMBM is the flag to indicate if the Intel RDT MBM is enabled. MBM (Memory Bandwidth Monitoring) supports monitoring of
-	// total and local memory bandwidth for the container.
-	EnableMBM bool `json:"enableMBM,omitempty"`
+	// EnableMonitoring enables resctrl monitoring for the container. This will
+	// create a dedicated resctrl monitoring group for the container.
+	EnableMonitoring bool `json:"enableMonitoring,omitempty"`
 }
 
 // ZOS contains platform-specific configuration for z/OS based containers.