linux-kernel - Re: [PATCH v2 29/35] fs/resctrl: Add boiler plate for external resctrl code

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Message-ID: <c9efc671-549f-4fb5-96fb-0948badbcef1@arm.com>
Date: Fri, 14 Jun 2024 14:59:16 +0100
From: James Morse <james.morse@....com>
To: Dave Martin <Dave.Martin@....com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Cc: Fenghua Yu <fenghua.yu@...el.com>,
 Reinette Chatre <reinette.chatre@...el.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>,
 Babu Moger <Babu.Moger@....com>, shameerali.kolothum.thodi@...wei.com,
 D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, "Shaopeng Tan (Fujitsu)"
 <tan.shaopeng@...itsu.com>, baolin.wang@...ux.alibaba.com,
 Jamie Iles <quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
 Peter Newman <peternewman@...gle.com>, dfustini@...libre.com,
 amitsinght@...vell.com, David Hildenbrand <david@...hat.com>,
 Rex Nie <rex.nie@...uarmicro.com>
Subject: Re: [PATCH v2 29/35] fs/resctrl: Add boiler plate for external
 resctrl code

Hi Dave,

On 26/04/2024 16:08, Dave Martin wrote:
> From: James Morse <james.morse@....com>
> 
> Add Makefile and Kconfig for fs/resctrl. Add ARCH_HAS_CPU_RESCTRL
> for the common parts of the resctrl interface and make X86_CPU_RESCTRL
> depend on this.


> FYI: Dave Martin, James Morse (et al.):
> 
>  * Review the new Kconfig RESCTRL_FS help text.
> 
>  * Because RESCTRL_FS combines a userspace interface and a kernel
>    library providing services to its own backends, there is a circular
>    dependency between this option and the arch-specific options
>    (CONFIG_X86_RESCTRL and eventually CONFIG_ARM64_MPAM) that
>    nastifies the presentation of these options in Kconfig.
> 
>    Can this be improved?
> 
>    The current situation works, but is not very user-friendly for
>    menuconfig users.

I don't follow what the circular dependency is - Kconfig would bark if there was one.

I agree its odd that you can't disable the filesystem under the filesystem menu - but that
is so that the existing Kconfig symbol name remains the switch for this. It's possible
no-one cares about that...

A more obvious approach would be a switch for the arch hardware feature, that when enabled
allows the filesystem to be selected. This seems overkill as there is only one user.


Thanks,

James