linux-kernel - Re: [RFC PATCH v3 10/17] x86/resctrl: Add data structures for ABMC assignment

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Date: Thu, 9 May 2024 19:28:42 -0500
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, babu.moger@....com,
 corbet@....net, fenghua.yu@...el.com, tglx@...utronix.de, mingo@...hat.com,
 bp@...en8.de, dave.hansen@...ux.intel.com
Cc: 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: [RFC PATCH v3 10/17] x86/resctrl: Add data structures for ABMC
 assignment

Hi Reinette,

On 5/7/2024 6:06 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 5/7/2024 1:40 PM, Moger, Babu wrote:
>> On 5/3/24 18:32, Reinette Chatre wrote:
>>> On 3/28/2024 6:06 PM, Babu Moger wrote:
>>>> ABMC (Bandwidth Monitoring Event Configuration) counters can be configured
>>>> by writing to L3_QOS_ABMC_CFG MSR. When ABMC is enabled, the user can
>>>> configure a counter by writing to L3_QOS_ABMC_CFG setting the CfgEn field
>>>> while specifying the Bandwidth Source, Bandwidth Types, and Counter
>>>> Identifier. Add the MSR definition and individual field definitions.
>>>>
>>>> MSR L3_QOS_ABMC_CFG (C000_03FDh) definitions.
>>>>
>>>> ==========================================================================
>>>> Bits 	Mnemonic	Description		Access Type   Reset Value
>>>> ==========================================================================
>>>> 63 	CfgEn 		Configuration Enable 	R/W 		0
>>>>
>>>> 62 	CtrEn 		Counter Enable 		R/W 		0
>>>>
>>>> 61:53 	– 		Reserved 		MBZ 		0
>>>>
>>>> 52:48 	CtrID 		Counter Identifier	R/W		0
>>>>
>>>> 47 	IsCOS		BwSrc field is a COS	R/W		0
>>>> 			(not an RMID)
>>>>
>>>> 46:44 	–		Reserved		MBZ		0
>>>>
>>>> 43:32	BwSrc		Bandwidth Source	R/W		0
>>>> 			(RMID or COS)
>>>>
>>>> 31:0	BwType		Bandwidth types to	R/W		0
>>>> 			track for this counter
>>>> ==========================================================================
>>>>
>>>> The feature details are documentd in the APM listed below [1].
> 
> documentd -> documented

Sure.
> 
>>>> [1] AMD64 Architecture Programmer's Manual Volume 2: System Programming
>>>> Publication # 24593 Revision 3.41 section 19.3.3.3 Assignable Bandwidth
>>>> Monitoring (ABMC).
>>>
>>> This changelog is purely a summary of the hardware architecture. I have not come
>>> across a clear explanation on how this architecture is intended to be supported
>>> by resctrl. When would resctrl need/want to set particular fields? What is
>>> the mapping to resctrl?
>>
>> Something like this in the changelog?
>>
>> ABMC feature provides an option to assign(or pin) an RMID to the
>> hardware counter and monitor the bandwidth for a longer duration.
> 
> Regarding "a longer duration":
> https://lore.kernel.org/lkml/b5e68d85-4bf2-4e55-a9c1-b39cb7d94db6@intel.com/

Sure. Will take care of this.
> 
>>
>> Hardware counters can be configured by writing to L3_QOS_ABMC_CFG MSR.
>> Configuration is done by setting the CfgEn field while specifying the
>> Bandwidth Source(RMID or CLOS), Bandwidth Types, and Counter Identifier.
>>
>> Add the configuration register definition.
> 
> This still looks to me like a cryptic description of the hardware architecture.
> Could you please spell out to me how the above answers each of my questions?

Will try to elaborate this in next revision.
Thanks
- Babu Moger