Re: [PATCH v4 00/19] x86/resctrl : Support AMD Assignable Bandwidth Monitoring Counters (ABMC)

Moger, Babu
2024-06-21T16:41:16Z

Hi Reinette,

On 6/20/2024 5:49 PM, Reinette Chatre wrote:
> Hi Babu,
>
> On 6/18/24 2:02 PM, Moger, Babu wrote:
>> On 6/13/24 19:54, Reinette Chatre wrote:
>>> On 5/24/24 5:23 AM, Babu Moger wrote:
>>>
>>>>     when reading, then the read will come back as Unavailable.
>>>
>>> Should this not rather be "Unassigned"? According to the docs the
>>> counters
>>> will return "Unavailable" right after reconfigure so it seems that there
>>> are scenarios where an "assigned" counter returns "Unavailable". It
>>> seems
>>> more
>>> useful to return "Unassigned" that will have a new specific meaning that
>>> overloading existing "Unavailable" that has original meaning of "try
>>> again" ....
>>> but in this case trying again will be futile.
>>
>> Hardware returns "Unavailable" in both the cases. So, thought of
>> reporting the same without any interpretation.
>>
>
> I do not see these as the same. When a counter is assigned and its
> read returns "Unavailable" then the user reasonably expects that
> retry will work.
> When a counter is not assigned then no amount of retries will result
> in data. How is user space expected to distinguish between the two
> scenarios that return the same error with such significantly different
> meaning? rdtgroup_mondata_shows() can just peek into the monitor
> group state and see if a counter is assigned and immediately
> return "Unassigned" if no counter is assigned, no? I see no need
> for it to IPI another CPU and try to read a counter that it already knows
> will be futile. This seems unnecessary and the generic "Unavailable" is
> not helpful to user space.
>

Sure. Will change it to report "Unassigned" in these cases.
Thanks
--
- Babu Moger