linux-kernel - Re: [PATCH v14 06/32] x86/cpufeatures: Add support for Assignable Bandwidth Monitoring Counters (ABMC)

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Message-ID: <df5f6ece-0fca-4e4c-a6e8-df48da276353@amd.com>
Date: Wed, 25 Jun 2025 11:28:38 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 tony.luck@...el.com, Dave.Martin@....com, james.morse@....com,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, akpm@...ux-foundation.org,
 rostedt@...dmis.org, paulmck@...nel.org, thuth@...hat.com, ardb@...nel.org,
 gregkh@...uxfoundation.org, seanjc@...gle.com, thomas.lendacky@....com,
 pawan.kumar.gupta@...ux.intel.com, manali.shukla@....com,
 perry.yuan@....com, kai.huang@...el.com, peterz@...radead.org,
 xiaoyao.li@...el.com, kan.liang@...ux.intel.com, mario.limonciello@....com,
 xin3.li@...el.com, gautham.shenoy@....com, xin@...or.com,
 chang.seok.bae@...el.com, fenghuay@...dia.com, peternewman@...gle.com,
 maciej.wieczor-retman@...el.com, eranian@...gle.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v14 06/32] x86/cpufeatures: Add support for Assignable
 Bandwidth Monitoring Counters (ABMC)

Hi Reinette,

On 6/24/25 16:31, Reinette Chatre wrote:
> Hi Babu,
> 
> On 6/13/25 2:04 PM, Babu Moger wrote:
>> Users can create as many monitor groups as RMIDs supported by the hardware.
>> However, bandwidth monitoring feature on AMD system only guarantees that
>> RMIDs currently assigned to a processor will be tracked by hardware. The
>> counters of any other RMIDs which are no longer being tracked will be reset
>> to zero. The MBM event counters return "Unavailable" for the RMIDs that are
>> not tracked by hardware. So, there can be only limited number of groups
>> that can give guaranteed monitoring numbers. With ever changing
>> configurations there is no way to definitely know which of these groups are
>> being tracked for certain point of time. Users do not have the option to
>> monitor a group or set of groups for certain period of time without
>> worrying about RMID being reset in between.
>>
>> The ABMC feature allows users to assign a hardware counter ID to an RMID,
>> event pair and monitor bandwidth usage as long as it is assigned. The
>> hardware continues to track the assigned counter until it is explicitly
>> unassigned by the user. There is no need to worry about counters being
>> reset during this period. Additionally, the user can specify a particular
>> type of memory transactions for the counter to track.
> 
> Looks like grammar updates from cover letter did not make it into this
> copied text. For example,
> "being tracked for certain point of time" -> "being tracked during a particular time"
> "for certain period of time" -> "for a certain period of time"
> "specify a particular type of memory transactions" -> "specify the type of
> memory transactions (e.g., reads, writes)"

Yes. Missed it. Will take of it now.
-- 
Thanks
Babu Moger