config-linux: documentation change for Intel RDT/MBA Software Control…

…ler support

MBA Software Controller feature is introduced in Linux kernel v4.18.
It is a software enhancement to mitigate some limitations in MBA which
describes in kernel documentation. It also makes the interface more user
friendly - we could specify memory bandwidth in "MBps" (Mega Bytes per
second) as well as in "percentages".

We could enable this feature through mount option "-o mba_MBps":
mount -t resctrl resctrl -o mba_MBps /sys/fs/resctrl

In runtime-spec, we handle both memory bandwidth schemata in unified
format: "MB:<cache_id0>=bandwidth0;<cache_id1>=bandwidth1;..."
The unit of memory bandwidth is specified in "percentages" by default,
and in "MBps" if MBA Software Controller is enabled.

For more information about Intel RDT and MBA Software Controller:
https://www.kernel.org/doc/Documentation/x86/intel_rdt_ui.txt

Signed-off-by: Xiaochen Shen <xiaochen.shen@intel.com>

config-linux.md

@@ -500,7 +500,7 @@ The following parameters can be specified for the container:
 
 * **`l3CacheSchema`** *(string, OPTIONAL)* - specifies the schema for L3 cache id and capacity bitmask (CBM).
     The value SHOULD start with `L3:` and SHOULD NOT contain newlines.
-* **`memBwSchema`** *(string, OPTIONAL)* - specifies the schema of memory bandwidth percentage per L3 cache id.
+* **`memBwSchema`** *(string, OPTIONAL)* - specifies the schema of memory bandwidth per L3 cache id.
     The value MUST start with `MB:` and MUST NOT contain newlines.
 
     If both `l3CacheSchema` and `memBwSchema` are set, runtimes MUST write the combined value to the `schemata` file in that sub-directory discussed in `closID`.

specs-go/config.go

@@ -632,7 +632,9 @@ type LinuxIntelRdt struct {
 	// Format: "L3:<cache_id0>=<cbm0>;<cache_id1>=<cbm1>;..."
 	L3CacheSchema string `json:"l3CacheSchema,omitempty"`
 
-	// The schema of memory bandwidth percentage per L3 cache id
+	// The schema of memory bandwidth per L3 cache id
 	// Format: "MB:<cache_id0>=bandwidth0;<cache_id1>=bandwidth1;..."
+	// The unit of memory bandwidth is specified in "percentages" by
+	// default, and in "MBps" if MBA Software Controller is enabled.
 	MemBwSchema string `json:"memBwSchema,omitempty"`
 }