linux-kernel - Re: [PATCH v8 08/25] x86/resctrl: Introduce interface to display number of monitoring counters

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Message-ID: <91f63f7b-32e8-4a67-9851-1c080fe62e23@amd.com>
Date: Mon, 14 Oct 2024 12:46:17 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 Tony Luck <tony.luck@...el.com>
Cc: corbet@....net, fenghua.yu@...el.com, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
 hpa@...or.com, paulmck@...nel.org, rdunlap@...radead.org, tj@...nel.org,
 peterz@...radead.org, yanjiewtw@...il.com, kim.phillips@....com,
 lukas.bulwahn@...il.com, seanjc@...gle.com, jmattson@...gle.com,
 leitao@...ian.org, jpoimboe@...nel.org, rick.p.edgecombe@...el.com,
 kirill.shutemov@...ux.intel.com, jithu.joseph@...el.com,
 kai.huang@...el.com, kan.liang@...ux.intel.com,
 daniel.sneddon@...ux.intel.com, pbonzini@...hat.com, sandipan.das@....com,
 ilpo.jarvinen@...ux.intel.com, peternewman@...gle.com,
 maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, eranian@...gle.com, james.morse@....com
Subject: Re: [PATCH v8 08/25] x86/resctrl: Introduce interface to display
 number of monitoring counters

Hi Reinette,

On 10/14/24 11:25, Reinette Chatre wrote:
> Hi Babu and Tony,
> 
> On 10/10/24 8:12 AM, Moger, Babu wrote:
>>
>> All good points. How about this text:
>>
>> "num_mbm_cntrs":
>> The number of monitoring counters available for assignment when the
>> architecture supports mbm_cntr_assign mode.
>>
>> Resctrl subsystem provides the interface to count maximum of two memory
> 
> subsystem -> filesystem

Sure.
> 
>> bandwidth events per group, from a combination of available total and
> 
> Is this "from a combination of ..." snippet intended to hint at BMEC?

No. We support 2 MBM events right now. That is why I added combination of
total and local. I can remove that text.


> 
>> local events. Keeping the current interface, users can enable a maximum of
> 
> What is meant by "Keeping the current interface"? Which interface? What will
> "current" mean when a user reads this documentation?

I meant not to change any interface to support mbm_cntrl_assign feature.

> 
>> 2 counters per group. User will also have the option to enable only one
> 
> "User will also have" is talking about the future. When will this be the case?

Again.. will have change the text here.

> 
>> counter to the group to maximize the number of groups monitored.
>>
>>
> 
> I think that we need to be careful when making this documentation so specific
> to the ABMC implementation. We already know that "soft-ABMC" is coming and
> Peter already shared [1] that with software assignment it will not be possible
> to assign counters to individual events. 
> 
> The goal of this work is to create a generic interface and this is the documentation
> for it. If this documentation is created to be specific to the first implementation
> it will make it difficult to use this same interface to support other
> implementations.
> 

Agree.

How about this?


"num_mbm_cntrs":
The number of monitoring counters available for assignment when the
architecture supports mbm_cntr_assign mode.

The resctrl filesystem allows user track up to two memory bandwidth events
per group, using a mix of total and local events. Users can enable up to 2
counters per group. There's also an option to enable just one counter per
group, which allows monitoring more groups.


-- 
Thanks
Babu Moger