linux-kernel - Re: [PATCH v14 30/32] fs/resctrl: Hide the BMEC related files when mbm

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Message-ID: <2b49620c-f2b0-4994-8617-e436725d0cf6@amd.com>
Date: Tue, 8 Jul 2025 08:27:20 -0500
From: "Moger, Babu" <bmoger@....com>
To: babu.moger@....com, Reinette Chatre <reinette.chatre@...el.com>,
 corbet@....net, tony.luck@...el.com, Dave.Martin@....com,
 james.morse@....com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, akpm@...ux-foundation.org,
 rostedt@...dmis.org, paulmck@...nel.org, thuth@...hat.com, ardb@...nel.org,
 gregkh@...uxfoundation.org, seanjc@...gle.com, thomas.lendacky@....com,
 pawan.kumar.gupta@...ux.intel.com, manali.shukla@....com,
 perry.yuan@....com, kai.huang@...el.com, peterz@...radead.org,
 xiaoyao.li@...el.com, kan.liang@...ux.intel.com, mario.limonciello@....com,
 xin3.li@...el.com, gautham.shenoy@....com, xin@...or.com,
 chang.seok.bae@...el.com, fenghuay@...dia.com, peternewman@...gle.com,
 maciej.wieczor-retman@...el.com, eranian@...gle.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v14 30/32] fs/resctrl: Hide the BMEC related files when
 mbm_event mode is enabled

Hi Reinette,

On 7/7/2025 5:35 PM, Moger, Babu wrote:
> Hi Reinette,
> 
> 
> On 7/3/25 11:21, Reinette Chatre wrote:
>> Hi Babu,
>>
>> On 7/2/25 12:04 PM, Moger, Babu wrote:
>>> Hi Reinette,
>>>
>>> On 7/2/25 12:21, Reinette Chatre wrote:
>>>> Hi Babu,
>>>>
>>>> On 7/2/25 9:42 AM, Moger, Babu wrote:
>>>>> On 6/25/25 18:39, Reinette Chatre wrote:
>>>>>> Hi Babu,
>>>>>>
>>>>>> On 6/13/25 2:05 PM, Babu Moger wrote:
>>>>>>> BMEC (Bandwidth Monitoring Event Configuration) and mbm_event mode do not
>>>>>>> work simultaneously.
>>>>>>
>>>>>> Could you please elaborate why they do not work simultaneously?
>>>>>
>>>>> Changed the changelog.
>>>>>
>>>>> When mbm_event counter assignment mode is enabled, events are configured
>>>>> through the "event_filter" files under
>>>>> /sys/fs/resctrl/info/L3_MON/event_configs/.
>>>>>
>>>>> The default monitoring mode and with BMEC (Bandwidth Monitoring Event
>>>>> Configuration) support, events are configured using the files
>>>>> mbm_total_bytes_config or mbm_local_bytes_config in
>>>>> /sys/fs/resctrl/info/L3_MON/.
>>>>
>>>> A reasonable question here may be why not just keep using the existing
>>>> (BMEC supporting) event configuration files for event configuration? Why
>>>> are new event configuration files needed?
>>>
>>> New interface that enables users to read and write memory transaction
>>> events using human-readable strings, simplifying configuration and
>>> improving usability.
>>
>> I find the "simplifying configuration and improving usability" a bit vague
>> for a changelog. The cover letter already claims that ABMC and BMEC are
>> incompatible and links to some email discussions. I think it will be helpful
>> to summarize here why ABMC and BMEC are considered incompatible and then use
>> that as motivation to hide BMEC. The motivation in this changelog is to
>> "avoid confusion" but the motivation is stronger than that.
>>
> 
> Changed the changelog. How does this look?
> 
> "The default monitoring mode and with BMEC (Bandwidth Monitoring Event
> Configuration) support, events are configured using the files
> mbm_total_bytes_config or mbm_local_bytes_config in
> /sys/fs/resctrl/info/L3_MON/.
> 
> When the mbm_event counter assignment mode is enabled, event configuration
> is handled via the event_filter files under
> /sys/fs/resctrl/info/L3_MON/event_configs/. This mode allows users to read
> and write memory transaction events using human-readable strings, making
> the interface easier to use and more intuitive. Going forward, this
> mechanism can support assigning multiple counters to RMID, event pairs and
> may be extended to allow flexible, user-defined event names.
> 
> Given these changes, hide the BMEC-related files when the mbm_event
> counter assignment mode is enabled. Also, update the mon_features display
> accordingly."
> 

Here is another update.

fs/resctrl: Hide the BMEC related files when mbm_event mode is enabled

The default monitoring mode and with BMEC (Bandwidth Monitoring Event
Configuration) support, events are configured using the files
mbm_total_bytes_config or mbm_local_bytes_config in
/sys/fs/resctrl/info/L3_MON/.

When the mbm_event counter assignment mode is enabled, event 
configuration is handled via the event_filter files under
/sys/fs/resctrl/info/L3_MON/event_configs/. This mode enables users to
configure memory transaction events using human-readable strings, 
providing a more intuitive and user-friendly interface. In the future, 
this mechanism could be extended to support assigning multiple counters 
to RMID-event pairs, as well as customizable, user-defined event names. 
Also, the presence of BMEC-related configuration files may cause 
confusion when the mbm_event counter assignment mode is enabled.

To address this, these files are now hidden when the mode is active.
Additionally, the mon_features display has been updated to reflect this
change.