linux-kernel - Re: [EXT] Re: [RFC 00/12] ARM: MPAM: add support for priority partitioning control

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Message-ID: <ZaBgUOQ3iWs3hLrb@agluck-desk3>
Date: Thu, 11 Jan 2024 13:40:32 -0800
From: Tony Luck <tony.luck@...el.com>
To: Peter Newman <peternewman@...gle.com>
Cc: Amit Singh Tomar <amitsinght@...vell.com>,
	Reinette Chatre <reinette.chatre@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"fenghua.yu@...el.com" <fenghua.yu@...el.com>,
	"james.morse@....com" <james.morse@....com>,
	George Cherian <gcherian@...vell.com>,
	"robh@...nel.org" <robh@...nel.org>
Subject: Re: [EXT] Re: [RFC 00/12] ARM: MPAM: add support for priority
 partitioning control

On Thu, Jan 11, 2024 at 12:56:34PM -0800, Peter Newman wrote:
> Hi Amit,
> 
> On Thu, Aug 24, 2023 at 1:52 AM Amit Singh Tomar <amitsinght@...vell.com> wrote:
> 
> > 2) Second approach that we discussed internally is to have schemata for CPOR, and PPART separated by new line as mentioned/suggested by Peter, But it may require to tweak
> >    the ARM MPAM device driver a bit. It was kind of toss-up between 2nd and 3nd approach :), and we went with the 3rd one.
> >
> >    L3:0=XXXX
> >    L3:0=PPART=X

I'm not sure having multiple lines for the same resource makes anything
clearer.  I preferred one of the earlier proposals like this one:

	L3:0=XXXX,PPART=X,CCAP=X;1=YYYY,CCAP=Y

This makes the schemata file self enumerate which optional capabilities
are present for each L3 instance (in the above example the second
instance doesn't support PPART, but does support CCAP).

Writes to the schemata file already accept partial information, so
the resctrl schemata_write() function should be coded to allow any of:

Just update CCAP for L3 instance 1":
	# echo "L3:1=CCAP=Z" > schemata

Update mask and CCAP for instance 0:
	# echo "L3:0=ABCD,CCAP=Q" > schemata

Update PPART on all instances:
	# echo "L3:0=PPART=M;1=PPART=N" > schemata

Legacy app that only comprehends partioning updates instance 1:
	# echo "L3:1=FFFF" > schemata

-Tony