linux-kernel - Re: [PATCH v6 02/42] x86/resctrl: Add a helper to avoid reaching into the arch code resource list

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Message-ID: <17f0c99a-3e9b-487a-8f32-b3ce0ecbbfff@arm.com>
Date: Fri, 28 Feb 2025 19:53:43 +0000
From: James Morse <james.morse@....com>
To: babu.moger@....com, x86@...nel.org, linux-kernel@...r.kernel.org
Cc: 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>,
 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,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
 Dave Martin <dave.martin@....com>, Koba Ko <kobak@...dia.com>,
 Shanker Donthineni <sdonthineni@...dia.com>,
 Shaopeng Tan <tan.shaopeng@...fujitsu.com>, Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v6 02/42] x86/resctrl: Add a helper to avoid reaching into
 the arch code resource list

Hi Babu,

(please don't top post!)

On 27/02/2025 20:24, Moger, Babu wrote:
> On 2/7/25 12:17, James Morse wrote:
>> Resctrl occasionally wants to know something about a specific resource,
>> in these cases it reaches into the arch code's rdt_resources_all[]
>> array.
>>
>> Once the filesystem parts of resctrl are moved to /fs/, this means it
>> will need visibility of the architecture specific struct
>> rdt_hw_resource definition, and the array of all resources.  All
>> architectures would also need a r_resctrl member in this struct.
>>
>> Instead, abstract this via a helper to allow architectures to do
>> different things here. Move the level enum to the resctrl header and
>> add a helper to retrieve the struct rdt_resource by 'rid'.
>>
>> resctrl_arch_get_resource() should not return NULL for any value in
>> the enum, it may instead return a dummy resource that is
>> !alloc_enabled && !mon_enabled.


>  You probably missed few cases here.
>
> static int logical_rmid_to_physical_rmid(int cpu, int lrmid)
> {
>   struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
> --
>
> }
>
> Any reason not use the new call resctrl_arch_get_resource() here?

Simply there is no need to! That code doesn't get moved to /fs/, so it doesn't need to use
a helper. Taken to its extreme - after the code is moved to /fs/, there are no callers of
resctrl_arch_get_resource() in the arch code, because whatever they do today is sufficent.


Thanks,

James