linux-kernel - Re: [PATCH v9 09/26] x86/resctrl: Introduce interface to display number of monitoring counters

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Message-ID: <35fc70fd-0281-4ac8-b32b-efa2f4516901@amd.com>
Date: Mon, 18 Nov 2024 15:31:28 -0600
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, peternewman@...gle.com
Cc: fenghua.yu@...el.com, x86@...nel.org, hpa@...or.com, thuth@...hat.com,
 paulmck@...nel.org, rostedt@...dmis.org, akpm@...ux-foundation.org,
 xiongwei.song@...driver.com, pawan.kumar.gupta@...ux.intel.com,
 daniel.sneddon@...ux.intel.com, perry.yuan@....com, sandipan.das@....com,
 kai.huang@...el.com, xiaoyao.li@...el.com, seanjc@...gle.com,
 jithu.joseph@...el.com, brijesh.singh@....com, xin3.li@...el.com,
 ebiggers@...gle.com, andrew.cooper3@...rix.com, mario.limonciello@....com,
 james.morse@....com, tan.shaopeng@...itsu.com, tony.luck@...el.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 peternewman@...gle.com, maciej.wieczor-retman@...el.com, eranian@...gle.com,
 jpoimboe@...nel.org, thomas.lendacky@....com
Subject: Re: [PATCH v9 09/26] x86/resctrl: Introduce interface to display
 number of monitoring counters

Hi Reinette,

On 11/15/24 18:06, Reinette Chatre wrote:
> Hi Babu,
> 
> On 10/29/24 4:21 PM, Babu Moger wrote:
>> The mbm_cntr_assign mode provides an option to the user to assign a
>> counter to an RMID, event pair and monitor the bandwidth as long as
>> the counter is assigned. Number of assignments depend on number of
>> monitoring counters available.
>>
>> Provide the interface to display the number of monitoring counters
>> supported. The interface file 'num_mbm_cntrs' is available when an
>> architecture supports mbm_cntr_assign mode.
>>
> 
> As mentioned in previous patch, do you think it may be possible to
> have a value for num_mbm_cntrs for non-ABMC AMD systems? If that is
> available and always exposed to user space (irrespective of
> mbm_cntr_assign mode) then it would be clear to user space on
> benefits/risks of running a "default" mode.

I am trying the work-around to get the number of max active RMIDs in
default mode. The method is to loop through all of the recently assigned
RMID's to see if any of their QM_CTR.U bits transition from 0->1.

I am not successful in getting it to work so far. I remember Peter was
trying this before in soft-ABMC. Peter, Any success with that?

If it does not work then our best option is to document it.

-- 
Thanks
Babu Moger