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fs/resctrl: Introduce the interface to display monitoring modes

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Introduce the resctrl file "mbm_assign_mode" to list the supported counter
assignment modes.

The "mbm_event" counter assignment mode allows users to assign a hardware
counter to an RMID, event pair and monitor bandwidth usage as long as it is
assigned. The hardware continues to track the assigned counter until it is
explicitly unassigned by the user. Each event within a resctrl group can be
assigned independently in this mode.

On AMD systems "mbm_event" mode is backed by the ABMC (Assignable Bandwidth
Monitoring Counters) hardware feature and is enabled by default.

The "default" mode is the existing mode that works without the explicit
counter assignment, instead relying on dynamic counter assignment by hardware
that may result in hardware not dedicating a counter resulting in monitoring
data reads returning "Unavailable".

Provide an interface to display the monitor modes on the system.

  $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
  [mbm_event]
  default

Add IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED) check to support Arm64.

On x86, CONFIG_RESCTRL_ASSIGN_FIXED is not defined. On Arm64, it will be
defined when the "mbm_event" mode is supported.

Add IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED) check early to ensure the user
interface remains compatible with upcoming Arm64 support. IS_ENABLED() safely
evaluates to 0 when the configuration is not defined.

As a result, for MPAM, the display would be either:

  [default]

or

  [mbm_event]

Signed-off-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com
This commit is contained in:
Babu Moger
2025-09-05 16:34:09 -05:00
committed by Borislav Petkov (AMD)
parent faebbc58cd
commit 3b497c3f4f
4 changed files with 73 additions and 1 deletions
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31
Documentation/filesystems/resctrl.rst
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@@ -257,6 +257,37 @@ with the following files:
# cat /sys/fs/resctrl/info/L3_MON/mbm_local_bytes_config
0=0x30;1=0x30;3=0x15;4=0x15
"mbm_assign_mode":
The supported counter assignment modes. The enclosed brackets indicate which mode
is enabled.
::
# cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
[mbm_event]
default
"mbm_event":
mbm_event mode allows users to assign a hardware counter to an RMID, event
pair and monitor the bandwidth usage as long as it is assigned. The hardware
continues to track the assigned counter until it is explicitly unassigned by
the user. Each event within a resctrl group can be assigned independently.
In this mode, a monitoring event can only accumulate data while it is backed
by a hardware counter. Use "mbm_L3_assignments" found in each CTRL_MON and MON
group to specify which of the events should have a counter assigned. The number
of counters available is described in the "num_mbm_cntrs" file. Changing the
mode may cause all counters on the resource to reset.
"default":
In default mode, resctrl assumes there is a hardware counter for each
event within every CTRL_MON and MON group. On AMD platforms, it is
recommended to use the mbm_event mode, if supported, to prevent reset of MBM
events between reads resulting from hardware re-allocating counters. This can
result in misleading values or display "Unavailable" if no counter is assigned
to the event.
"max_threshold_occupancy":
Read/write file provides the largest value (in
bytes) at which a previously used LLC_occupancy