linux-kernel - Re: [RFC PATCH 03/19] fs/resctrl: Add new interface max

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Message-ID: <aa594520-b21a-4c45-95b3-59d3f79de603@amd.com>
Date: Mon, 9 Feb 2026 17:52:45 -0600
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 Babu Moger <babu.moger@....com>, corbet@....net, tony.luck@...el.com,
 Dave.Martin@....com, james.morse@....com, tglx@...nel.org, mingo@...hat.com,
 bp@...en8.de, dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, peterz@...radead.org,
 juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com,
 rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, akpm@...ux-foundation.org,
 pawan.kumar.gupta@...ux.intel.com, pmladek@...e.com,
 feng.tang@...ux.alibaba.com, kees@...nel.org, arnd@...db.de,
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Subject: Re: [RFC PATCH 03/19] fs/resctrl: Add new interface max_bandwidth

Hi Reinette,

Thanks for the comments. Will try to respond one by one.

On 2/6/2026 5:58 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 1/21/26 1:12 PM, Babu Moger wrote:
>> While min_bandwidth is exposed for each resource under
>> /sys/fs/resctrl, the maximum supported bandwidth is not currently shown.
>>
>> Add max_bandwidth to report the maximum bandwidth permitted for a resource.
>> This helps users understand the limits of the associated resource control
>> group.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> 
> With resctrl fs being used by several architectures we should take care that
> interface changes take all planned usages into account.
> 
> As shared at LPC [1] and email [2] we are already trying to create an interface
> that works for everybody and it already contains a way to expose the maximum
> bandwidth to user space. You attended that LPC session and [2] directed to you
> received no response. This submission with a different interface is unexpected.

Thanks for pointing this out. Yes. I missed that thread.

> Reinette
> 
> [1] https://lpc.events/event/19/contributions/2093/attachments/1958/4172/resctrl%20Microconference%20LPC%202025%20Tokyo.pdf
> [2] https://lore.kernel.org/lkml/fb1e2686-237b-4536-acd6-15159abafcba@intel.com/

I need to look into this much closely. Our current plan is to support MB 
and GMBA with L3 scope. So, with that in mind, I am not seeing a use 
case in that context for now. I can remove exposing max_bandwidth until 
we have a unified approach.

Thanks
Babu