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

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Message-ID: <456e0266-2ec5-41a8-8808-080c8b9607d8@amd.com>
Date: Mon, 14 Oct 2024 13:51:37 -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 13:30, Reinette Chatre wrote:
> Hi Babu,
> 
> On 10/14/24 10:46 AM, Moger, Babu wrote:
>> On 10/14/24 11:25, Reinette Chatre wrote:
>>> 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
> 
> "a mix of" remains unclear to me since there are only two options. I think we
> can be specific here.
> 
>> counters per group. There's also an option to enable just one counter per
>> group, which allows monitoring more groups.
>>
> 
> How about below for the second paragraph:
> 
> 	The resctrl filesystem supports tracking up to two memory bandwidth
> 	events per monitoring group: mbm_total_bytes and/or mbm_local_bytes.
> 	Up to two counters can be assigned per monitoring group, one for each
> 	memory bandwidth event. More monitoring groups can be tracked by
> 	assigning one counter per monitoring group. However, doing so limits
> 	memory bandwidth tracking to a single memory bandwidth event per
> 	monitoring group.
>  

Sure. Looks good.
-- 
Thanks
Babu Moger