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Signed-off-by: Fenghua Yu --- Documentation/filesystems/resctrl.rst | 52 +++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst index a88ea9c2a386..6027b2f9aa15 100644 --- a/Documentation/filesystems/resctrl.rst +++ b/Documentation/filesystems/resctrl.rst @@ -1087,6 +1087,58 @@ down and recreated, so a concurrent reader may briefly observe the control subdirectories are informational only and the actual bandwidth configuration in each group's ``schemata`` file is unaffected. +The following illustrates one such configuration on ARM MPAM. + +ARM MPAM example +~~~~~~~~~~~~~~~~ +On ARM MPAM systems where the MBA resource is backed by a memory-level +MSC, the kernel exposes two bandwidth controls: + +``MB`` (default): + The legacy control. When the L3 cache MSC has usable MBA hardware, + this control is backed by cache-level MBW (``mbw_max``) hardware, + its ``status`` reads ``enabled``, and its ``scope`` reads ``L3``. + The ``MB:`` schemata line uses L3 cache identifiers. + +``MB_NODE``: + The native, node-scoped control. When the memory MSC has usable MBA + hardware, this control is backed by node-level MBW hardware, its + ``status`` reads ``enabled``, and its ``scope`` reads ``NODE``. + The ``MB_NODE:`` schemata line uses NUMA node identifiers. + +``MB_NODE`` is the native control that emulates ``MB`` in legacy mode +when ``MB`` has no MBW hardware of its own. + +``MB_NODE`` is only created on a memory-class MBA resource, and such a +resource is only registered when it has usable MBA hardware, so whenever +``MB_NODE`` is present its ``status`` reads ``enabled``. (If ``MB_NODE`` +is not supported it is simply absent from ``info/MB/resource_schemata/``.) +The control subdirectory layout therefore depends only on the ``MB`` +control's ``status`` (the trees below show ``legacy`` mode; in ``native`` +mode every control is a sibling directly under ``resource_schemata/``): + +**MB disabled, MB_NODE enabled** (``MB`` emulated by ``MB_NODE``):: + + info/MB/resource_schemata/ + ├── mode + └── MB/ + ├── scope # NODE + ├── status # disabled + └── MB_NODE/ + ├── scope # NODE + └── status # enabled + +**MB enabled, MB_NODE enabled**:: + + info/MB/resource_schemata/ + ├── mode + ├── MB/ + │ ├── scope # L3 + │ └── status # enabled + └── MB_NODE/ + ├── scope # NODE + └── status # enabled + Memory bandwidth Allocation specified in MiBps ---------------------------------------------- -- 2.43.0