linux-kernel - Re: [PATCH v13 14/27] x86/resctrl: Add the functionality to unassign MBM events

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Message-ID: <dc2ac138-10fc-4e0f-bb50-1f9d5df82918@amd.com>
Date: Thu, 29 May 2025 11:25:56 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 tony.luck@...el.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
Cc: james.morse@....com, dave.martin@....com, fenghuay@...dia.com,
 x86@...nel.org, hpa@...or.com, paulmck@...nel.org,
 akpm@...ux-foundation.org, thuth@...hat.com, rostedt@...dmis.org,
 ardb@...nel.org, gregkh@...uxfoundation.org, daniel.sneddon@...ux.intel.com,
 jpoimboe@...nel.org, alexandre.chartre@...cle.com,
 pawan.kumar.gupta@...ux.intel.com, thomas.lendacky@....com,
 perry.yuan@....com, seanjc@...gle.com, kai.huang@...el.com,
 xiaoyao.li@...el.com, kan.liang@...ux.intel.com, xin3.li@...el.com,
 ebiggers@...gle.com, xin@...or.com, sohil.mehta@...el.com,
 andrew.cooper3@...rix.com, mario.limonciello@....com,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 peternewman@...gle.com, maciej.wieczor-retman@...el.com, eranian@...gle.com,
 Xiaojian.Du@....com, gautham.shenoy@....com
Subject: Re: [PATCH v13 14/27] x86/resctrl: Add the functionality to unassign
 MBM events

Hi Reinette,

On 5/22/25 17:49, Reinette Chatre wrote:
> Hi Babu,
> 
> On 5/15/25 3:51 PM, Babu Moger wrote:
>> The mbm_cntr_assign mode offers "num_mbm_cntrs" number of counters that
>> can be assigned to an RMID, event pair and monitor the bandwidth as long
>> as it is assigned. If all the counters are in use, the kernel will log the
>> error message "Unable to allocate counter in domain" in
>> /sys/fs/resctrl/info/last_cmd_status when a new assignment is requested.
>>
>> To make space for a new assignment, users must unassign an already
>> assigned counter and retry the assignment again.
>>
>> Add the functionality to unassign and free the counters in the domain.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> ...
> 
>> ---
>>  fs/resctrl/internal.h |  2 ++
>>  fs/resctrl/monitor.c  | 60 +++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 62 insertions(+)
>>
>> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
>> index ce4fcac91937..64ddc107fcab 100644
>> --- a/fs/resctrl/internal.h
>> +++ b/fs/resctrl/internal.h
>> @@ -379,6 +379,8 @@ int resctrl_find_cleanest_closid(void);
>>  
>>  int resctrl_assign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>>  			      struct rdtgroup *rdtgrp, enum resctrl_event_id evtid);
>> +int resctrl_unassign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +				struct rdtgroup *rdtgrp, enum resctrl_event_id evtid);
>>  
>>  #ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
>>  int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
>> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
>> index d76fd0840946..fbc938bd3b23 100644
>> --- a/fs/resctrl/monitor.c
>> +++ b/fs/resctrl/monitor.c
>> @@ -989,6 +989,14 @@ static int mbm_cntr_alloc(struct rdt_resource *r, struct rdt_mon_domain *d,
>>  	return -ENOSPC;
>>  }
>>  
>> +/*
>> + * mbm_cntr_free() -  Reset cntr_id to zero.
> 
> "Reset cntr_id to zero"? cntr_id is an index to an array.
> Please provide accurate and useful descriptions.

Yes. My bad. Will correct it.

> 
>> + */
>> +static void mbm_cntr_free(struct rdt_mon_domain *d, int cntr_id)
>> +{
>> +	memset(&d->cntr_cfg[cntr_id], 0, sizeof(struct mbm_cntr_cfg));
>> +}
>> +
>>  /*
>>   * mbm_get_mon_event() - Return the mon_evt entry for the matching evtid.
>>   */
>> @@ -1068,3 +1076,55 @@ int resctrl_assign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>>  
>>  	return ret;
>>  }
>> +
>> +/*
>> + * Unassign and free the counter if assigned.
>> + */
>> +static int resctrl_free_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +				    struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
>> +{
>> +	struct mon_evt *mevt;
>> +	int cntr_id;
>> +
>> +	cntr_id = mbm_cntr_get(r, d, rdtgrp, evtid);
>> +
>> +	/* If there is no cntr_id assigned, nothing to do */
>> +	if (cntr_id < 0)
>> +		return 0;
>> +
>> +	mevt = mbm_get_mon_event(r, evtid);
>> +	if (!mevt) {
>> +		rdt_last_cmd_printf("Invalid event id %d\n", evtid);
> 
> Similar to previous comment this is in kernel bug territory and could be simplified
> by passing mon_evt instead. Although this is the unassign portion where 
> evt_cfg seems unnecessary.

Sure. The call mbm_get_mon_event() is not required anymore in this path.

> 
>> +		return -EINVAL;
>> +	}
>> +
>> +	resctrl_config_cntr(r, d, evtid, rdtgrp->mon.rmid, rdtgrp->closid,
>> +			    cntr_id, mevt->evt_cfg, false);
>> +
>> +	mbm_cntr_free(d, cntr_id);
>> +
>> +	return 0;
>> +}
>> +
>> +/*
>> + * Unassign a hardware counter associated with @evtid from the domain and
>> + * the group. Unassign the counters from all the domains if @d is NULL else
>> + * unassign from @d.
>> + */
>> +int  resctrl_unassign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +				 struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
>> +{
>> +	int ret;
>> +
>> +	if (!d) {
>> +		list_for_each_entry(d, &r->mon_domains, hdr.list) {
>> +			ret = resctrl_free_config_cntr(r, d, rdtgrp, evtid);
>> +			if (ret)
>> +				return ret;
>> +		}
>> +	} else {
>> +		ret = resctrl_free_config_cntr(r, d, rdtgrp, evtid);
>> +	}
>> +
>> +	return ret;
>> +}
> 
> Reinette
> 

-- 
Thanks
Babu Moger