Re: RE: RE: [PATCH 1/2] x86/resctrl, Documentation: Keep mbm_assign_mode "default" on boot

[Babu Moger <babu.moger@amd.com>]

Hi Tony,

On 7/28/26 15:24, Luck, Tony wrote:
>>> 1) Does it start over from zero?
>>>      Seems a sane option.
>>> 2) Or does the monitor group see whatever the counter was at
>>> when being used by some other group?
>>>      Seems less sane.
>>
>> As per this code, it should start over from 0.
>>
>>    } else if (ret == -EINVAL) {
>>                   am = get_arch_mbm_state(hw_dom, rmid, eventid);
>>                   if (am)
>>                           am->prev_msr = 0;
>>           }
> 
> Nope. If you want the value reported to the user to start over from zero,
> then prev_msr should be set to the current value of the counter. That
> would make the next read start from zero.
> 
When an RMID is reallocated, the hardware detects the state transition 
and the first read returns "Unavailable". At that point, the counter is 
reset and begins counting again from 0. This is the expected behavior on 
AMD systems. Therefore, setting prev_msr to 0 is the correct behavior.

Thanks
Babu