linux-kernel - Re: [PATCH v5 19/24] x86/resctrl: Add helpers for system wide mon/alloc capable

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Message-ID: <2a0ba79b-b085-7f9d-3cfd-bdb4feda1edd@arm.com>
Date:   Thu, 24 Aug 2023 17:57:21 +0100
From:   James Morse <james.morse@....com>
To:     Fenghua Yu <fenghua.yu@...el.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>,
        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, 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>, peternewman@...gle.com,
        dfustini@...libre.com
Subject: Re: [PATCH v5 19/24] x86/resctrl: Add helpers for system wide
 mon/alloc capable

Hi Fenghua,

On 17/08/2023 19:34, Fenghua Yu wrote:
> On 7/28/23 09:42, James Morse wrote:
>> resctrl reads rdt_alloc_capable or rdt_mon_capable to determine
>> whether any of the resources support the corresponding features.
>> resctrl also uses the static-keys that affect the architecture's
>> context-switch code to determine the same thing.
>>
>> This forces another architecture to have the same static-keys.
>>
>> As the static-key is enabled based on the capable flag, and none of
>> the filesystem uses of these are in the scheduler path, move the
>> capable flags behind helpers, and use these in the filesystem
>> code instead of the static-key.
>>
>> After this change, only the architecture code manages and uses
>> the static-keys to ensure __resctrl_sched_in() does not need
>> runtime checks.
>>
>> This avoids multiple architectures having to define the same
>> static-keys.
>>
>> Cases where the static-key implicitly tested if the resctrl
>> filesystem was mounted all have an explicit check added by a
>> previous patch.

> Why isn't rdt_alloc_capable in get_rdt_alloc_resources() replaced by the helper?
> 
> static __init bool get_rdt_alloc_resources(void)
> {
> ...
>         if (rdt_alloc_capable)
> ...

Because its in core.c, and is only called by get_rdt_resources as part of the arch codes
resctrl_late_init(). This can stay as it is once the filesystem code is moved out to
/fs/resctrl, there was no need to touch it.


Thanks,

James