linux-kernel - Re: resctrl2

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Date:   Fri, 25 Aug 2023 11:58:08 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     "Luck, Tony" <tony.luck@...el.com>,
        Amit Singh Tomar <amitsinght@...vell.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "james.morse@....com" <james.morse@....com>,
        George Cherian <gcherian@...vell.com>,
        "robh@...nel.org" <robh@...nel.org>,
        "peternewman@...gle.com" <peternewman@...gle.com>,
        Drew Fustini <dfustini@...libre.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: resctrl2 - status

Hi Tony,

On 8/25/2023 11:09 AM, Luck, Tony wrote:
>> Alternatively, can user space just take a "load all resctrl modules
>> and see what sticks" (even modules of different architectures since
>> a user space may want to be generic) approach? 
> 
> This mostly works. Except for the cases where different modules access
> the same underlying hardware, so can't be loaded together.
> 
> Examples:
> 
> rdt_l3_cat vs. rdt_l3_cdp - user needs to decide whether they want CDP or not.
> But this is already true ... they have to decide whether to pass the "-o cdp" option
> to mount.
> 
> rdt_l3_mba vs. rdt_l3_mba_MBps - does the user want to control memory bandwidth
> with percentages, or with MB/sec values. Again the user already has to make this
> decision when choosing mount options.
> 
> 
> Maybe the "What resctrl options does this machine support?" question would be
> best answered with a small utility?

A user space utility or a kernel provided utility? If it is a user space utility
I think it would end up needing to duplicate what the kernel is required to do
to know if a particular feature is supported. It seems appropriate that this
could be a kernel utility that can share this existing information with user
space. resctrl already supports the interface for this via /sys/fs/resctrl/info.

fyi ... as with previous attempts to discuss this work I find it difficult
to discuss this work when you are selective about what you want to discuss/answer
and just wipe the rest. Through this I understand that I am not your target
audience.

Reinette