linux-kernel - Re: [PATCH v8 07/25] x86/resctrl: Introduce the interface to display monitor mode

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Message-ID: <87d9bf3c-4916-46fa-b07f-c44d5295ba35@intel.com>
Date: Fri, 11 Oct 2024 15:24:57 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: <babu.moger@....com>, "Luck, Tony" <tony.luck@...el.com>
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Subject: Re: [PATCH v8 07/25] x86/resctrl: Introduce the interface to display
 monitor mode



On 10/10/24 8:30 AM, Moger, Babu wrote:
> On 10/10/24 10:07, Luck, Tony wrote:
>>>>> +  By default resctrl assumes each control and monitor group has a hardware
>>>>> +  counter. Hardware that does not support 'mbm_cntr_assign' mode will still
>>>>> +  allow more control or monitor groups than 'num_rmids' to be created. In
>>>>
>>>> Should that be s/num_rmids/num_mbm_cntrs/ ?
>>>
>>> It is actually num_rmids here as in default mode, num_rmid_cntrs are not
>>> available.
>>
>> Babu,
>>
>> The code isn't working that way for me. I built & booted. Since I'm on
>> an Intel machine without ABMC I'm in "default" mode. But I can't make
>> more monitor groups that num_rmids.
>>
> 
> That is correct. We will have to change the text. How about?
> 
> "default":
> By default resctrl assumes each control and monitor group has a hardware
> counter. Hardware that does not support 'mbm_cntr_assign' mode will still

I think this is independent from whether hardware supports 'mbm_cntr_assign'
mode since a user could enable 'default' mode on hardware that supports 
'mbm_cntr_assign'. This snippet is thus more about what is meant by 'default'
mode than what is supported by hardware.

The docs already contain:
	"num_rmids":
		...
		This is the upper bound for how many "CTRL_MON" + "MON"
		groups can be created.


Neither of the 'mbm_assign_mode' options change this meaning of 'num_rmids' (i.e.
no change in how many monitor groups can be created) so mentioning it in the
'default' portion but not in the 'mbm_cntr_assign' portion may create confusion.


Perhaps it can be simplified to:
	In default mode resctrl assumes each CTRL_MON and MON group has a
	hardware counter. Reading mbm_total_bytes or mbm_local_bytes may
	report 'Unavailable' if there is no counter associated with that
	group.


> allow to create control or monitor groups up to num_rmids supported. In
> that case reading the mbm_total_bytes and mbm_local_bytes may report
> 'Unavailable' if there is no counter associated with that group.
> 

Reinette