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

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Message-ID: <SJ1PR11MB60839C1BA84823B44376B90AFC682@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Thu, 11 Jan 2024 23:14:34 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Chatre, Reinette" <reinette.chatre@...el.com>, Peter Newman
	<peternewman@...gle.com>
CC: Amit Singh Tomar <amitsinght@...vell.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "Yu, Fenghua" <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

>> 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 assumes that all tools (public and private) that currently parse the schemata
> file will be able to handle this additional information seamlessly.

Reinette,

Yes. If there are tools that *read* schemata files, they will be surprised by this extra information.

But that also applies if the "extra" information is moved to a second line that also begins with "L3:".

Tools that *write* schemata files should be OK as long as the kernel will still accept:

  # echo "L3:1=fff" > schemata

E.g. the Linux selftests in tools/testing/selftests/resctrl/ should still run without
any modification.

The "separate line" option could work if the prefix isn't "L3:".  E.g.

L3:0=XXXX;1=YYYY
L3PPART:0=X
L3CCAP:0=X;1=Y

If these options are asymmetrically available on cache instances, these extra
lines won't have every L3 cache instance listed.

-Tony