Re: [RFC] mpam,x86,fs/resctrl: Generic schema description Proof of Concept

[Ben Horgan <ben.horgan@arm.com>]

Hi Tony,

On 7/16/26 17:02, Luck, Tony wrote:
>>> This was one element of original discussion that fizzled a bit since it was not obvious that user
>>> space would behave like this. Consider, for example, from Documentation/filesystems/resctrl.rst:
>>>
>>>     Reading/writing the schemata file
>>>     ---------------------------------
>>>     ... When writing you only need to specify those values which you wish to change. ..
>>
>> Yeah, I don't know but it does seem like something a user could reasonably expect to work.
> 
> Personally I use one of two options to update schemata:
> 
> 1) Just want to change something small:
> 	# echo "MB:1=50" > schemata
> 2) I want to make global change to some resource
> 	# vi schemata
> 		on L2 line: s/ffff/ff/g
> 	:wq
> 
> In case 2 every domain on every resource is written, but most of them to the existing value.

We've got a user :)

> 
> This may need careful consideration if the legacy "MB" lines are present together with the
> new controls for MIN, MAX etc.
> 
> Having a mode file to select whether legacy OR native controls are exposed would avoid
> a lot of complexity in the kernel. Yes, that would mean a user that wants to use the new
> native interface must add one "echo" to some startup script.
> 
> Or perhaps yet another "rdt=" command line option to pick whether mount defaults to
> legacy or native mode?

The "rdt=" options are x86 specific so I don't think we should use them for generic resctrl. A mount
option might be end up being convenient.

Thanks,

Ben

> 
> -Tony