linux-kernel - Re: [PATCH v7 13/24] x86/resctrl: Add data structures and definitions for ABMC assignment

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Message-ID: <a8055c81-331f-4204-9069-3a7d1b3594f0@amd.com>
Date: Tue, 24 Sep 2024 09:51:43 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.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: [PATCH v7 13/24] x86/resctrl: Add data structures and definitions
 for ABMC assignment

Hi Reinette,

On 9/23/24 17:30, Reinette Chatre wrote:
> Hi Babu,
> 
> On 9/23/24 1:21 PM, Moger, Babu wrote:
>> Hi Reinette,
>>
>> On 9/19/24 12:08, Reinette Chatre wrote:
>>> Hi Babu,
>>>
>>> On 9/4/24 3:21 PM, Babu Moger wrote:
>>>> +/*
>>>> + * ABMC counters can be configured by writing to L3_QOS_ABMC_CFG.
>>>> + * @bw_type		: Bandwidth configuration(supported by BMEC)
>>>> + *			  tracked by the @cntr_id.
>>>> + * @bw_src		: Bandwidth source (RMID or CLOSID).
>>>> + * @reserved1		: Reserved.
>>>> + * @is_clos		: @bw_src field is a CLOSID (not an RMID).
>>>> + * @cntr_id		: Counter identifier.
>>>> + * @reserved		: Reserved.
>>>> + * @cntr_en		: Tracking enable bit.
>>>> + * @cfg_en		: Configuration enable bit.
>>>> + *
>>>> + * Configuration and tracking:
>>>> + * CfgEn=1,CtrEn=0 : Configure CtrID and but no tracking the events yet.
>>>> + * CfgEn=1,CtrEn=1 : Configure CtrID and start tracking events.
>>>
>>> Thanks for moving the text ... could it now be made to match the new (outside
>>> AMD arch document) destination? For example, "CfgEn" becomes "@cfg_en",
>>
>> Sure. Will do.
>>
>>> "CtrID" becomes "@cntr_id" etc. Also please fix language, for example
>>> what does "and but no tracking the events yet" mean? So far this work
>>> has focused on "counting" vs "not counting" events and it is not
>>
>> I will change the text to "not counting".  Hope this will clarify here.
>>
>>> clear how this "tracking" fits it ... this seems to be the hardware
>>> view that means "tracking the RMID to which @cntr_id is assigned"?
>>> Please help readers to understand how the implementation is supported
>>> by the hardware.
>>
>> I have checked with hw team on this.
>> CfgEn: This corresponds counter assignment.
> 
> To be specific this corresponds to *hardware* counter assignment? This is
> because software sets CfgEn to 1 whether it is assigned from kernel perspective
> or not.

Yes. We are setting CfgEn = 1 in both assign/unassign.

In case of unassign, we want the counter to stop counting so that software
does not get confused. Otherwise it is really not required.


> 
> Actually ... when I look at the AMD spec it becomes more clear to me. If I
> understand the spec correctly the CfgEn bit is used to coordinate changes
> between OS and HW. Seems like OS can leisurely write to any fields of
> L3_QOS_ABMC_CFG, but only when CfgEn bit is set will the actual hardware
> configuration be performed.
> 
>> CtrEn: This is to start or stop counting.
>>        We always set this to 1 to start counting.
> 
> Understood. Now that I read this portion of AMD spec it is more clear to me
> and I understand why CfgEn is set in both counter assign and unassign.
> 
> Reinette
> 

-- 
Thanks
Babu Moger