linux-kernel - Re: [PATCH v11 00/23] x86/resctrl : Support AMD Assignable Bandwidth Monitoring Counters (ABMC)

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Message-ID: <7853e74f-661f-4e24-beb8-560998f230d6@amd.com>
Date: Thu, 20 Mar 2025 15:29:15 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, "Moger, Babu"
 <bmoger@....com>, Peter Newman <peternewman@...gle.com>
Cc: "Luck, Tony" <tony.luck@...el.com>, Dave Martin <Dave.Martin@....com>,
 corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 paulmck@...nel.org, akpm@...ux-foundation.org, thuth@...hat.com,
 rostedt@...dmis.org, xiongwei.song@...driver.com,
 pawan.kumar.gupta@...ux.intel.com, daniel.sneddon@...ux.intel.com,
 jpoimboe@...nel.org, perry.yuan@....com, sandipan.das@....com,
 kai.huang@...el.com, xiaoyao.li@...el.com, seanjc@...gle.com,
 xin3.li@...el.com, andrew.cooper3@...rix.com, ebiggers@...gle.com,
 mario.limonciello@....com, james.morse@....com, tan.shaopeng@...itsu.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 maciej.wieczor-retman@...el.com, eranian@...gle.com
Subject: Re: [PATCH v11 00/23] x86/resctrl : Support AMD Assignable Bandwidth
 Monitoring Counters (ABMC)

Hi Reinette,

On 3/19/25 15:53, Reinette Chatre wrote:
> Hi Babu and Peter,
> 
> On 3/17/25 4:00 PM, Moger, Babu wrote:
>> Hi Peter,
>>
>> On 3/17/2025 11:27 AM, Peter Newman wrote:
>>> Hi Reinette,
>>>
>>> On Thu, Mar 13, 2025 at 10:22 PM Reinette Chatre
>>> <reinette.chatre@...el.com> wrote:
>>>>
>>>> Hi Babu,
>>>>
>>>> On 3/13/25 1:13 PM, Moger, Babu wrote:
>>>>> On 3/13/25 11:08, Reinette Chatre wrote:
>>>>>> On 3/12/25 11:14 AM, Moger, Babu wrote:
>>>>>>> On 3/12/25 12:14, Reinette Chatre wrote:
>>>>>>>> On 3/12/25 9:03 AM, Moger, Babu wrote:
>>>>>>>>> On 3/12/25 10:07, Reinette Chatre wrote:
>>>>
>>>>
>>>>> Here are the steps. Just copying steps from Peters proposal.
>>>>> https://lore.kernel.org/lkml/CALPaoCiii0vXOF06mfV=kVLBzhfNo0SFqt4kQGwGSGVUqvr2Dg@mail.gmail.com/
>>>>
>>>> Thank you very much for detailing the steps. It is starting the fall into place
>>>> for me.
>>>>
>>>>>
>>>>>
>>>>> 1. Mount the resctrl
>>>>>     mount -t resctrl resctrl /sys/fs/resctrl
>>>>
>>>> I assume that on ABMC system the plan remains to have ABMC enabled by default, which
>>>> will continue to depend on BMEC.
>>>>
>>>> How would the k existing BMEC implementation be impacted in this case?
>>>>
>>>> Without any changes to BMEC support the mbm_total_bytes_config and mbm_local_bytes_config
>>>> files will remain and user space may continue to use them to change the event
>>>> configurations with confusing expecations/results on an ABMC system.
>>>>
>>>> One possibility may be that a user may see below on ABMC system even if BMEC is supported:
>>>> # cat /sys/fs/resctrl/info/L3_MON/mon_features
>>>> llc_occupancy
>>>> mbm_total_bytes
>>>> mbm_local_bytes
>>>>
>>>> With the above a user cannot be expected to want to interact with mbm_total_bytes_config
>>>> and mbm_local_bytes_config, which may be the simplest to do.
>>>
>>> How about making mbm_local_bytes and mbm_total_bytes always be
>>> configured using mbm_{local,total}_bytes_config and only allowing the
>>> full ABMC configurability on user-defined configurations. This could
>>> resolve the issue of backwards compatibility with the BMEC files and
>>> remove the need for the user opting-in to ABMC mode.
> 
> hmmm, yes, backward compatibility is a big issue with an earlier suggestion
> from me. Users with scripts/tools using mbm_{local,total}_bytes_config
> would expect that to continue to work on systems that support BMEC.
> resctrl could continue to use mbm_{local,total}_bytes_config
> even though the inconsistent interface is not ideal
> 
>>
>> There is no opt-in mode. ABMC will be enabled by default if supported.
>> Users will have option to go back to legacy mode.
> 
> I assume there will still be the opt-in for automatic counter assignment
> on monitor group creation (mkdir)?

Yes. It will be available.
-- 
Thanks
Babu Moger