linux-kernel - Re: [RFC PATCH 0/2] Resctrl

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Date:   Wed, 28 Jun 2023 11:43:13 +0200
From:   Peter Newman <peternewman@...gle.com>
To:     Tony Luck <tony.luck@...el.com>
Cc:     James Morse <james.morse@....com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Drew Fustini <dfustini@...libre.com>,
        Babu Moger <Babu.Moger@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        shameerali.kolothum.thodi@...wei.com,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        carl@...amperecomputing.com, lcherian@...vell.com,
        bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
        xingxin.hx@...nanolis.org, baolin.wang@...ux.alibaba.com,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>,
        Nicolas Pitre <npitre@...libre.com>,
        Kevin Hilman <khilman@...libre.com>, aricciardi@...libre.com,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev, Stephane Eranian <eranian@...gle.com>
Subject: Re: [RFC PATCH 0/2] Resctrl - rewrite (WIP)

Hi Tony,

On Tue, Jun 20, 2023 at 5:37 AM Tony Luck <tony.luck@...el.com> wrote:
>
> Back in April I posted some RFC patches that added a "driver
> registration" interface to the core resctrl code so that additional
> resource control and monitor features could be added without further
> complicating the core code. Link to that discussion:
>
> https://lore.kernel.org/all/20230420220636.53527-1-tony.luck@intel.com/
>
> Reinette gave the feedback that it would be better to base the module
> registration on the resctrl resource structure. Reinette also pointed
> me to work from James Morse, and some additional discussion happened
> here:
>
> https://lore.kernel.org/all/ZG%2FMZVrWYrCHm%2Ffr@agluck-desk3/
>
> James provided details on where ARM's MPAM has similarities and
> differences from the Intel Resource Director Technology and AMD's
> similar implementation. Drew Fustini was also pulled into that
> conversation to comment on RISC-V CBQRI.
>
> From those discussions I believed we need a do-over on the core
> /sys/fs/resctrl implementation to make it friendlier for architecural
> variations. Here's what I have so far.
>
> =========================================================================
> | N.B. This is a general direction check. There are many obvious        |
> | rough edges (e.g. some careful thought needs to happen on locking     |
> | for the files in /sys/fs/resctrl that are "owned" by modules that     |
> | can be unloaded). I'm mostly looking for feedback from AMD, ARM and   |
> | RISCV on whether this is a foundation to build on, whether some small |
> | tweaks could make it better, or if this is still going to be really   |
> | hard for architectures that have radical divergence from the Intel    |
> | model.                                                                |
> =========================================================================

Thanks for working on this! I played with these changes locally on
some of our machines and they seemed reasonably functional so far and
was happy to see dynamically adding and removing resources working.

I will need to try working with the code to give it a serious
evaluation, though. Would you consider it ready for me to try
re-implementing soft RMIDs on it?

I'm also very interested in James's opinion and what this means for
the ongoing MPAM upstreaming.

Thanks!
-Peter