Message-ID: <95e675a6-5cec-4f14-bb57-eebffb6024a5@amd.com>
Date: Thu, 26 Jun 2025 14:31:50 -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 18/32] fs/resctrl: Add the functionality to assign MBM
 events



On 6/24/25 22:32, Reinette Chatre wrote:
> Hi Babu,
> 
> On 6/13/25 2:05 PM, Babu Moger wrote:
>> When supported "mbm_event" mode offers "num_mbm_cntrs" number of counters
> 
> "When supported, "mbm_event" counter assignment mode offers ..."?

Sure.

> 
>> that can be assigned to RMID, event pairs and monitor bandwidth usage as
>> long as it is assigned.
>>
>> Add the functionality to allocate and assign a counter ID to an RMID, event
>> pair in the domain.
>>
>> If all the counters are in use, 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. Exit on the first failure when
>> assigning counters across all the domains.
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> 
> ...
> 
>> ---
>>  fs/resctrl/internal.h |   3 +
>>  fs/resctrl/monitor.c  | 134 ++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 137 insertions(+)
>>
>> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
>> index 71059c2cda16..0767a1c46f26 100644
>> --- a/fs/resctrl/internal.h
>> +++ b/fs/resctrl/internal.h
>> @@ -386,6 +386,9 @@ bool closid_allocated(unsigned int closid);
>>  
>>  int resctrl_find_cleanest_closid(void);
>>  
>> +int resctrl_assign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +			      struct rdtgroup *rdtgrp, struct mon_evt *mevt);
>> +
>>  #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 3e1a8239b0d3..38800fe45931 100644
>> --- a/fs/resctrl/monitor.c
>> +++ b/fs/resctrl/monitor.c
>> @@ -950,3 +950,137 @@ void resctrl_mon_resource_exit(void)
>>  
>>  	dom_data_exit(r);
>>  }
>> +
>> +/**
>> + * resctrl_config_cntr() - Configure the counter ID for the event, RMID pair in
>> + * the domain.
>> + *
>> + * Assign the counter if @assign is true else unassign the counter. Reset the
>> + * associated non-architectural state.
> 
> A few reports came through about the kernel-doc issues but I did not see a
> discussion finalize on how to resolve them. I do not think it is required for these
> static functions to have full kernel-doc. Just having useful comments without
> kernel-doc style is valuable. Some kernel-doc syntax can still be useful though, like
> above when referring to the parameters. It is ok to keep doing so even if section
> does not start with /**. 

Sure. Thanks

> 
> Where I think kernel-doc is important is include/linux/resctrl.h.

Sure.

> 
>> + */
>> +static void resctrl_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +				enum resctrl_event_id evtid, u32 rmid, u32 closid,
>> +				u32 cntr_id, bool assign)
> 
> If resctrl_arch_config_cntr() does not need a struct resource then resctrl_config_cntr()
> may not either?
> 
>> +{
>> +	struct mbm_state *m;
>> +
>> +	resctrl_arch_config_cntr(r, d, evtid, rmid, closid, cntr_id, assign);
>> +
>> +	m = get_mbm_state(d, closid, rmid, evtid);
>> +	if (m)
>> +		memset(m, 0, sizeof(struct mbm_state));
> 
> sizeof(*m).

Sure.

> 
>> +}
>> +
>> +/**
>> + * mbm_cntr_get() - Return the counter ID for the matching @evtid and @rdtgrp.
>> + *
>> + * Return:
>> + * Valid counter ID on success, or -ENOENT on failure.
>> + */
>> +static int mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +			struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
>> +{
>> +	int cntr_id;
>> +
> 
> Since mbm_cntr_get() is called in regular flows, could you please also
> add an explicit check to return -ENOENT if !r->mon.mbm_cntr_assignable?
> Otherwise this is quite subtle with the assumption that
> r->mon.num_mbm_cntrs is zero in this case.

Sure. Added the check.

if (!r->mon.mbm_cntr_assignable)
                return -ENOENT;


> 
>> +	if (!resctrl_is_mbm_event(evtid))
>> +		return -ENOENT;
>> +
>> +	for (cntr_id = 0; cntr_id < r->mon.num_mbm_cntrs; cntr_id++) {
>> +		if (d->cntr_cfg[cntr_id].rdtgrp == rdtgrp &&
>> +		    d->cntr_cfg[cntr_id].evtid == evtid)
>> +			return cntr_id;
>> +	}
>> +
>> +	return -ENOENT;
>> +}
>> +
>> +/**
>> + * mbm_cntr_alloc() - Initilialize and return a new counter ID in the domain @d.
> 
> "Initilialize" -> "Initialize"

Sure.

> 
>> + *
> 
> mbm_cntr_alloc() will allocate a counter to a RMID/event pair even
> if that pair already has a counter assigned. The doc should note that caveat
> here with documentation that the caller is responsible for checking that
> a counter is not already assigned.
Added the text.

Caller must ensure that the specified event is not assigned already.

> 
>> + * Return:
>> + * Valid counter ID on success, or -ENOSPC on failure.
>> + */
>> +static int mbm_cntr_alloc(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +			  struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
>> +{
>> +	int cntr_id;
>> +
>> +	for (cntr_id = 0; cntr_id < r->mon.num_mbm_cntrs; cntr_id++) {
>> +		if (!d->cntr_cfg[cntr_id].rdtgrp) {
>> +			d->cntr_cfg[cntr_id].rdtgrp = rdtgrp;
>> +			d->cntr_cfg[cntr_id].evtid = evtid;
>> +			return cntr_id;
>> +		}
>> +	}
>> +
>> +	return -ENOSPC;
>> +}
>> +
>> +/**
>> + * resctrl_alloc_config_cntr() - Allocate a counter ID and configure it for the
>> + * event pointed to by @mevt and the resctrl group @rdtgrp within the domain @d.
>> + *
>> + * Return:
>> + * 0 on success, or a non-zero value on failure.
> 
> "or a non-zero value on failure." -> "<0 on failure"

Sure.

> 
>> + */
>> +static int resctrl_alloc_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +				     struct rdtgroup *rdtgrp, struct mon_evt *mevt)
>> +{
>> +	int cntr_id;
>> +
>> +	/* No need to allocate a new counter if it is already assigned */
>> +	cntr_id = mbm_cntr_get(r, d, rdtgrp, mevt->evtid);
>> +	if (cntr_id >= 0)
>> +		goto cntr_configure;
>> +
>> +	cntr_id = mbm_cntr_alloc(r, d, rdtgrp, mevt->evtid);
>> +	if (cntr_id <  0) {
>> +		rdt_last_cmd_printf("Unable to allocate counter in domain %d\n",
>> +				    d->hdr.id);
>> +		return cntr_id;
>> +	}
>> +
>> +cntr_configure:
>> +	/*
>> +	 * Skip reconfiguration if the event setup is current; otherwise,
>> +	 * update and apply the new configuration to the domain.
> 
> When could "event setup" *not* be current? As mentioned in earlier patch
> I do not see why mon_evt::evt_cfg as well as mbm_cntr_cfg::evt_cfg is
> needed. There should be no need to keep these two "in sync" with
> only mon_evt::evt_cfg as the source of configuration. I seem to be missing
> something here, could you please detail this scenario?

As discussed earlier, removed the following check. Return success if the
counter is assigned already.

https://lore.kernel.org/lkml/887bad33-7f4a-4b6d-95a7-fdfe0451f42b@intel.com/

> 
>> +	 */
>> +	if (mevt->evt_cfg != d->cntr_cfg[cntr_id].evt_cfg) {
>> +		d->cntr_cfg[cntr_id].evt_cfg = mevt->evt_cfg;
>> +		resctrl_config_cntr(r, d, mevt->evtid, rdtgrp->mon.rmid,
>> +				    rdtgrp->closid, cntr_id, true);
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +/**
>> + * resctrl_assign_cntr_event() - Assign a hardware counter for the event in
>> + * @mevt to the resctrl group @rdtgrp. Assign counters to all domains if @d is
>> + * NULL; otherwise, assign the counter to the specified domain @d.
>> + *
>> + * If all counters in a domain are already in use, resctrl_alloc_config_cntr()
>> + * will fail. The assignment process will abort at the first failure encountered
>> + * during domain traversal, which may result in the event being only partially
>> + * assigned.
>> + *
>> + * Return:
>> + * 0 on success, or a non-zero value on failure.
> 
> "or a non-zero value on failure" -> "<0 on failure"
> 

Sure.

>> + */
>> +int resctrl_assign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +			      struct rdtgroup *rdtgrp, struct mon_evt *mevt)
>> +{
>> +	int ret = 0;
>> +
>> +	if (!d) {
>> +		list_for_each_entry(d, &r->mon_domains, hdr.list) {
>> +			ret = resctrl_alloc_config_cntr(r, d, rdtgrp, mevt);
>> +			if (ret)
>> +				return ret;
>> +		}
>> +	} else {
>> +		ret = resctrl_alloc_config_cntr(r, d, rdtgrp, mevt);
>> +	}
>> +
>> +	return ret;
>> +}
> 
> Reinette
> 

-- 
Thanks
Babu Moger

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