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

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Message-ID: <d5c4d3e8-6d5f-4892-83b5-867ec8bfc97a@intel.com>
Date: Thu, 3 Jul 2025 09:21:07 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: <babu.moger@....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>,
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Subject: Re: [PATCH v14 30/32] fs/resctrl: Hide the BMEC related files when
 mbm_event mode is enabled

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.

> 
> In future it can be extended to create free form event names.
> 
>>
>>>
>>> To avoid the confusion, hide BMEC-related files when mbm_event counter
>>> assignment mode is enabled and update the mon_features display accordingly.

Reinette