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: <dd52a51a-e0b1-4c5d-89d2-8732d4e9e2ff@intel.com>
Date: Fri, 21 Feb 2025 10:35:58 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: 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

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