Re: [PATCH v3 3/3] x86,fs/resctrl: Keep mbm_assign_mode in default mode at boot

[Reinette Chatre]

Hi Babu,

On 10/7/26 11:54 AM, Babu Moger wrote:
> On 10/6/26 12:53, Reinette Chatre wrote:
>> On 10/2/26 2:26 PM, Babu Moger wrote:
...
>>> workflows that monitor a subset of groups at a time and rotate
>>> assignments as needed.
>>>
>>> resctrl enables the "mbm_event" mode by default on hardware that
>>> supports it. That breaks the pqos tool [1], which assumes the historical
>>> default mode. pqos treats a non-numeric event read as zero bandwidth. It
>>> creates 16 or more monitoring groups and uses two counters per group.
>>> On a platform with 32 counters per domain, that consumes the pool, so
>>> further groups read "Unassigned" and pqos reports 0 MB/s for them:
>>>
>>>    $sudo pqos -m all:0-4
>>>    CORE         IPC      MISSES     LLC[KB]   MBL[MB/s]   MBR[MB/s]
>>>       0        0.69         16k       192.0         0.0         0.0
>>>       1        0.40          3k         0.0         0.0         0.0
>>>       2        0.44          1k        64.0         0.0         0.0
>>>       3        0.39          1k        64.0         0.0         0.0
>>>       4        0.43          1k         0.0         0.0         0.0
>>>
>>> Leave mbm_assign_mode in "default" mode during initialization. Default
>>> mode uses one counter per monitoring group. On existing AMD platforms
>>> that pool is 64 counters and may be larger on newer hardware. The
>>> "mbm_event" mode uses two counters per group, so 32 counters cover only
>>> 16 groups.
>>>
>>> Deployments within that pool receive accurate bandwidth measurements
>>> with default mode. The hardware supports 4096 monitoring groups. Beyond
>>> that pool, readings may be misleading or "Unavailable", with no
>>
>> At this point I am lost because the word "pool" is used to mean three
>> different things. It is used for the number of "ABMC counters" as well
>> as the number of "non-ABMC counters" that exist on the same platform,
>> above it seems to be used for number of RMIDs (number of monitoring
>> groups) also. Could you please add some context at beginning of
>> changelog to introduce the various counts applicable to the description,
>> associate unique terms to these counts at that time, and then use
>> those unique terms in the rest of the changelog?
> 
> Sure.
> I can name as "ABMC counters pool" and "default active counters pool"

hmmm ... "active counter" is new term that, when grepping this series,
fs/resctrl/*, and arch/x86/kernel/cpu/resctrl/*, does not appear a single
time.
If this new term is needed then please include a definition as part of the
changelog context that makes it obvious what it refers to.

Reinette