Re: [PATCH v14 11/32] fs/resctrl: Introduce the interface to display monitoring modes

[Moger, Babu]

Hi Reinette,

On 6/24/25 17:47, Reinette Chatre wrote:
> Hi Babu,
> 
> On 6/13/25 2:04 PM, Babu Moger wrote:
>> Introduce the resctrl file "mbm_assign_mode" to list the supported
>> monitoring modes.
> 
> "the supported monitoring modes" -> "the supported counter assignment modes"?

Sure.

> 
>>
>> The "mbm_event" mode allows users to assign a hardware counter ID to an
> 
> nit: users do not assign/pick the ID, this is done by resctrl. So perhaps
> just "users to assign a hardware counter to ..."

Sure.

> 
>> 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@xxxxxxx>
>> ---
> 
> ...
> 
>> ---
>>  Documentation/filesystems/resctrl.rst | 31 ++++++++++++++++++++++
>>  fs/resctrl/rdtgroup.c                 | 37 +++++++++++++++++++++++++++
>>  2 files changed, 68 insertions(+)
>>
>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>> index c97fd77a107d..4e76e4ac5d3a 100644
>> --- a/Documentation/filesystems/resctrl.rst
>> +++ b/Documentation/filesystems/resctrl.rst
>> @@ -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 monitoring modes. The enclosed brackets indicate which mode
> 
> "The supported monitoring modes." -> "The supported counter assignment modes."?
> 

Sure.

>> +	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 ID to an RMID, event
> 
> "hardware counter ID" -> "hardware counter"
> 

Sure.

>> +	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
> 
> Reinette
> 
> 

-- 
Thanks
Babu Moger