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

["Moger, Babu" <bmoger@amd.com>]

Hi Reinette,

On 10/7/2026 5:21 PM, Reinette Chatre wrote:
> 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.
> 

Sure. Will do.
Thanks
Babu