linux-kernel - Re: [PATCH v2 09/23] x86/resctrl: Switch over to the resctrl mbps

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Message-ID: <8dbfa092-685d-dc74-b8e5-449ad0ab5222@arm.com>
Date:   Wed, 27 Oct 2021 17:49:47 +0100
From:   James Morse <james.morse@....com>
To:     Reinette Chatre <reinette.chatre@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     Fenghua Yu <fenghua.yu@...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,
        Jamie Iles <jamie@...iainc.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        lcherian@...vell.com, bobo.shaobowang@...wei.com,
        tan.shaopeng@...itsu.com
Subject: Re: [PATCH v2 09/23] x86/resctrl: Switch over to the resctrl mbps_val
 list

Hi Reinette,

On 15/10/2021 23:26, Reinette Chatre wrote:
> On 10/1/2021 9:02 AM, James Morse wrote:
>> Updates to resctrl's software controller follow the same path as
>> other configuration updates, but they don't modify the hardware state.
>> rdtgroup_schemata_write() uses parse_line() and the resource's
>> ctrlval_parse function to stage the configuration.
> 
> parse_ctrlval ?
> 
>> resctrl_arch_update_domains() then updates the mbps_val[] array
>> instead, and resctrl_arch_update_domains() skips the rdt_ctrl_update()
>> call that would update hardware.
>>
>> This complicates the interface between resctrl's filesystem parts
>> and architecture specific code. It should be possible for mba_sc
>> to be completely implemented by the filesystem parts of resctrl. This
>> would allow it to work on a second architecture with no additional code.
>>
>> Change parse_bw() to write the configuration value directly to the
>> mba_sc[] array in the domain structure. Change rdtgroup_schemata_write()
> 
> mpbs_val[] array?
> 
>> to skip the call to resctrl_arch_update_domains(), meaning all the
>> mba_sc specific code in resctrl_arch_update_domains() can be removed.
>> On the read-side, show_doms() and update_mba_bw() are changed to read
>> the mba_sc[] array from the domain structure. With this,
> 
> mbps_val[] ?
> 
> Should rdtgroup_size_show() also get a similar snippet?

Yes! Good catch!


Thanks,

James