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Document the info/MB/schemata/ nesting, control_mode, and the legacy MB: versus native MB_NODE: schemata lines. Signed-off-by: Fenghua Yu --- Documentation/filesystems/resctrl.rst | 51 +++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst index fbce6a1bd4c4..450cf269472d 100644 --- a/Documentation/filesystems/resctrl.rst +++ b/Documentation/filesystems/resctrl.rst @@ -353,6 +353,57 @@ schemata file:: MB_MIN:0=1;1=1 MB_MAX:0=1000;1=1000 +ARM MPAM example +~~~~~~~~~~~~~~~~ +On ARM MPAM systems where the MBA resource is backed by a memory-level +MSC and the L3 cache MSC has no usable MBA hardware, the kernel exposes +two bandwidth controls. ``MB_NODE`` backs ``MB`` so legacy mode keeps a +working ``MB:`` schemata line. + +``MB`` (default): + The legacy control. It has no bandwidth hardware of its own, so + in ``legacy`` ``control_mode`` writes to the ``MB:`` line are + applied through ``MB_NODE``. Domain identifiers are NUMA node + ids. + +``MB_NODE``: + The native, node-scoped control backed by memory-level MBW + hardware. The ``MB_NODE:`` schemata line uses the same NUMA node + identifiers. The control directory is nested under ``MB`` in + ``info/MB/schemata/``. + +``MB_NODE`` is created only in that configuration. If the L3 cache MSC +already has usable MBA hardware, ``MB`` is backed by that cache-level +hardware and ``MB_NODE`` is not created. + +``control_mode`` lives in ``info/MB/``. Switching mode changes which +lines appear in each group's ``schemata`` file; it does not rebuild the +``info/MB/schemata/`` tree. + +**Memory-level MBA, no L3 MBA** (``MB`` emulated by ``MB_NODE``):: + + info/MB/ + ├── control_mode + └── schemata/ + └── MB/ + └── MB_NODE/ + +In ``legacy`` mode (the default) the group's schemata file shows the +emulated ``MB:`` line:: + + # cat /sys/fs/resctrl/info/MB/control_mode + [legacy] native + # cat schemata + MB:0=100;1=100 + +In ``native`` mode the ``MB:`` line is replaced by ``MB_NODE:``:: + + # echo native > /sys/fs/resctrl/info/MB/control_mode + # cat /sys/fs/resctrl/info/MB/control_mode + legacy [native] + # cat schemata + MB_NODE:0=100;1=100 + Resource control properties ~~~~~~~~~~~~~~~~~~~~~~~~~~~ Every control directory contains a file named "type" that specifies which -- 2.53.0