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

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Message-ID: <CALPaoCh9LsUDz9320i9tvgte2+DoRvnr-RiAMJiudAVFM6AUGA@mail.gmail.com>
Date:   Tue, 22 Aug 2023 11:01:08 +0200
From:   Peter Newman <peternewman@...gle.com>
To:     Amit Singh Tomar <amitsinght@...vell.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        fenghua.yu@...el.com, reinette.chatre@...el.com,
        james.morse@....com, gcherian@...vell.com, robh@...nel.org
Subject: Re: [RFC 00/12] ARM: MPAM: add support for priority partitioning control

Hi Amit,

On Tue, Aug 15, 2023 at 5:27 PM Amit Singh Tomar <amitsinght@...vell.com> wrote:
> As an example, "schemata" file under resource control group contains information about
> cache portion bitmaps, and memory bandwidth allocation, and these are used to configure
> Cache portion partition (CPOR), and MPAM bandwidth partitioning controls.
>
> MB:0=0100
> L3:0=ffff
>
> But resctrl doesn't provide a way to set-up other control that ARM MPAM provides
> (For instance, Priority partitioning control as mentioned above). To support this,
> James has suggested to use already existing schemata to be compatible with
> portable software, and this is the main idea behind this RFC is to have some kind
> of discussion on how resctrl can be extended to support priority partitioning control.
>
> To support Priority partitioning control, "schemata" file is updated to accommodate
> priority field (upon priority partitioning capability detection), separated from CPBM
> using delimiter ",".
>
> L3:0=ffff,f where f indicates downstream priority max value.

Do we really have to mash two controls into the same schema? In the
CDP example, the code/data controls are presented as multiple schema,
for example: "L3CODE, L3DATA"

Especially when reading back the schemata file, it seems like it would
be simpler for existing software to ignore unfamiliar schema lines in
the schemata file than to overlook the introduction of a comma to the
CBM in the existing "L3" schema.

Thanks!
-Peter