[PATCH RFC v1 0/6] arm_mpam,resctrl: expose MPAM MBW_MAX hard limit

[Fenghua Yu]

This series exposes the ARM MPAM MBW_MAX HARDLIM bit through resctrl.
The MBA schemata line sets the maximum bandwidth. HARDLIM selects
whether that maximum is a hard limit. It is a per-domain 0/1 value, not
another percentage, so it is a separate control on the MBA resource
rather than a second bandwidth percentage.

MPAMF_MBW_IDR.MAX_LIM reports how the implementation encodes that limit.
When the probed value is 0, this kernel treats HARDLIM as read/write.
When MAX_LIM is nonzero, or the platform has no hard-limit control, the
schemata line is omitted.

The line follows the MSC, the same way the bandwidth line does. A cache
MSC uses cache ids:

	       MB:1=100;2=100
	MB_MAXHLM:1=0;2=0

A memory-level MSC uses NUMA node ids:

	       MB_NODE:0=100;1=100
	MB_MAXHLM_NODE:0=0;1=0

Please advise if "MB_MAXHLM" on cache ids and "MB_MAXHLM_NODE" on
NUMA ids meet the new naming conventions.

0 clears HARDLIM (soft limit). 1 sets HARDLIM. New groups start with the
hard limit off. info/MB/schemata/MB_MAXHLM/max and
info/MB/schemata/MB_MAXHLM_NODE/max are 1. The bandwidth control's max
stays 100. The control directory under info/MB/schemata/ is MB_MAXHLM or
MB_MAXHLM_NODE.

The 6 patches are grouped as follows:

1. resctrl hard-limit control (patch 1)

   Parse MB_MAXHLM as a 0/1 value on the MBA resource, and initialize
   new groups with HARDLIM clear.

2. MPAM probe and config (patches 2-3)

   Read MAX_LIM from MPAMF_MBW_IDR, derive HARDLIM read/write when that
   encoding is 0, and keep the HARDLIM bit in mpam_config so later
   MBW_MAX programming does not drop it.

3. Wire the control (patch 4)

   Create the MAXHLM control on the MBA resource when HARDLIM is
   read/write, and read and write it through resctrl_arch_get_config()
   and resctrl_arch_update_one().

4. Node scope and documentation (patches 5-6)

   On a memory-level MSC, name the control MB_MAXHLM_NODE, set the
   resource scope to the NUMA node, and give the hard-limit control the
   range 0..1. Document both schemata lines.

The branch is on top CPU-less RFC V3 and resource controls RFC V2:
https://github.com/fyu1/linux/commits/hlim.rfc.v1

Testing

Brought up on an ARM MPAM platform whose MBA resource is a memory-level
MSC. resctrl mounts, and schemata lists MB_NODE and MB_MAXHLM_NODE with
NUMA node ids. Not tested on x86 beyond compilation of the resctrl
changes.

Fenghua Yu (6):
  resctrl: wire MB_MAXHLM schemata parsing and group setup
  arm_mpam: resctrl: probe MPAMF_MBW_IDR MAX_LIM and hardlim_rw
  arm_mpam: resctrl: track MBW max hard-limit in config
  arm_mpam: resctrl: add MAXHLM control on the MBA resource
  arm_mpam: Add MB_MAXHLM_NODE and Node scope
  Documentation: resctrl: document MB_MAXHLM for MPAM MBA

 Documentation/filesystems/resctrl.rst |  28 ++++
 drivers/resctrl/mpam_devices.c        |  67 ++++++++-
 drivers/resctrl/mpam_internal.h       |   8 ++
 drivers/resctrl/mpam_resctrl.c        | 191 +++++++++++++++++++++-----
 fs/resctrl/ctrlmondata.c              |  36 +++++
 fs/resctrl/rdtgroup.c                 |  17 +++
 include/linux/resctrl.h               |  16 ++-
 7 files changed, 325 insertions(+), 38 deletions(-)

-- 
2.53.0