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

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Message-ID: <16888c23-08d6-465d-83e5-b5612b46ea96@amd.com>
Date: Tue, 8 Jul 2025 10:43:44 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, "Moger, Babu"
 <bmoger@....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 7/8/25 10:21, Reinette Chatre wrote:
> Hi Babu,
> 
> On 7/8/25 6:27 AM, Moger, Babu wrote:
>> On 7/7/2025 5:35 PM, Moger, Babu wrote:
>>> On 7/3/25 11:21, Reinette Chatre wrote:
>>>> On 7/2/25 12:04 PM, Moger, Babu wrote:
>>>>> On 7/2/25 12:21, Reinette Chatre wrote:
>>>>>> On 7/2/25 9:42 AM, Moger, Babu wrote:
>>>>>>> On 6/25/25 18:39, Reinette Chatre wrote:
>>>>>>>> On 6/13/25 2:05 PM, Babu Moger wrote:

>>> 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.
> 
> I do not find a concrete motivation in this changelog. The terms "may cause
> confusion" and "providing a more intuitive and user-friendly interface." are
> vague and not something that I think provides a good motivation for disabling
> an entire interface.
> 
> I aim to write a draft below that I hope will help make this changelog more
> convincing. Please do improve it:
> 
> 
> 	fs/resctrl: Disable BMEC event configuration when mbm_event mode is enabled
> 
> 	The BMEC (Bandwidth Monitoring Event Configuration) feature enables per-domain
> 	event configuration. With BMEC the MBM events are configured using 
> 	the mbm_total_bytes_config or mbm_local_bytes_config files in
> 	/sys/fs/resctrl/info/L3_MON/ and the per-domain event configuration
> 	affects all monitor resource groups.
> 
> 	The mbm_event counter assignment mode enables counters to be assigned to
> 	RMID (i.e a monitor resource group), event pairs, with potentially unique
> 	event configurations associated	with every counter.
> 
> 	There may be systems that support both BMEC and mbm_event counter assignment
> 	mode, but resctrl supporting both concurrently will present a conflicting
> 	interface to the user with both per-domain and per RMID, event configurations
> 	active at the same time.
> 
> 	mbm_event counter assignment provides most flexibility to user space and
> 	aligns with Arm's counter support. On systems that support both, disable BMEC
> 	event configuration when mbm_event mode is enabled by hiding the
> 	the mbm_total_bytes_config or mbm_local_bytes_config files when mbm_event mode
> 	is enabled. Ensure mon_features always displays accurate information about
> 	monitor features.
> 	

Looks good.

-- 
Thanks
Babu Moger