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

[Luck, Tony]

> > 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.

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?

-Tony