linux-kernel - Re: [PATCH v11 11/23] x86/resctrl: Introduce mbm_cntr_cfg to track assignable counters at domain

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Message-ID: <d597f2c1-bcf3-4d00-8d48-1ebe95015245@amd.com>
Date: Fri, 21 Feb 2025 14:10:16 -0600
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 James Morse <james.morse@....com>, Babu Moger <babu.moger@....com>,
 corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, tony.luck@...el.com, peternewman@...gle.com
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org,
 akpm@...ux-foundation.org, thuth@...hat.com, rostedt@...dmis.org,
 xiongwei.song@...driver.com, pawan.kumar.gupta@...ux.intel.com,
 daniel.sneddon@...ux.intel.com, jpoimboe@...nel.org, perry.yuan@....com,
 sandipan.das@....com, kai.huang@...el.com, xiaoyao.li@...el.com,
 seanjc@...gle.com, xin3.li@...el.com, andrew.cooper3@...rix.com,
 ebiggers@...gle.com, mario.limonciello@....com, tan.shaopeng@...itsu.com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 maciej.wieczor-retman@...el.com, eranian@...gle.com
Subject: Re: [PATCH v11 11/23] x86/resctrl: Introduce mbm_cntr_cfg to track
 assignable counters at domain



On 2/21/2025 12:35 PM, Reinette Chatre wrote:
> Hi James,
> 
> On 2/21/25 10:07 AM, James Morse wrote:
>> Hi Babu,
>>
>> On 22/01/2025 20:20, Babu Moger wrote:
>>> In mbm_cntr_assign mode hardware counters are assigned/unassigned to an
>>> MBM event of a monitor group. Hardware counters are assigned/unassigned
>>> at monitoring domain level.
>>>
>>> Manage a monitoring domain's hardware counters using a per monitoring
>>> domain array of struct mbm_cntr_cfg that is indexed by the hardware
>>> counter	ID. A hardware counter's configuration contains the MBM event
>>> ID and points to the monitoring group that it is assigned to, with a
>>> NULL pointer meaning that the hardware counter is available for assignment.
>>>
>>> There is no direct way to determine which hardware counters are	assigned
>>> to a particular monitoring group. Check every entry of every hardware
>>> counter	configuration array in every monitoring domain to query which
>>> MBM events of a monitoring group is tracked by hardware. Such queries
>>> are acceptable because of a very small number of assignable counters.
>>
>>> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
>>> index 511cfce8fc21..9a54e307d340 100644
>>> --- a/include/linux/resctrl.h
>>> +++ b/include/linux/resctrl.h
>>> @@ -94,6 +94,18 @@ struct rdt_ctrl_domain {
>>>   	u32				*mbps_val;
>>>   };
>>>   
>>> +/**
>>> + * struct mbm_cntr_cfg - assignable counter configuration
>>> + * @evtid:		 MBM event to which the counter is assigned. Only valid
>>> + *			 if @rdtgroup is not NULL.
>>> + * @rdtgroup:		 resctrl group assigned to the counter. NULL if the
>>> + *			 counter is free.
>>> + */
>>> +struct mbm_cntr_cfg {
>>> +	enum resctrl_event_id	evtid;
>>> +	struct rdtgroup		*rdtgrp;
>>> +};
>>
>> struct rdtgroup here suggests this shouldn't be something the arch code is touching.
>>
>> If its not needed by any arch specific code, (I couldn't find a resctrl_arch helper that
>> takes this) - could it be moved to resctrl's internal.h.
>>
>> (If this does need to be visible to the arch code, one option would be to replace rdtgroup
>> with the closid/rmid, and a valid flag so that memset() continues to reset these entries)
>>
> 
> Thank you for catching this!
> 
> Reinette
> 
> 

Sure. Will move it to arch/x86/kernel/cpu/resctrl/internal.h.

thanks
Babu