Re: [PATCH v15 23/34] fs/resctrl: Support counter read/reset with mbm_event assignment mode

["Moger, Babu" <babu.moger@amd.com>]

Hi Reinette,

On 7/17/25 22:53, Reinette Chatre wrote:
> Hi Babu,
> 
> On 7/8/25 3:17 PM, Babu Moger wrote:
>> When "mbm_event" counter assignment mode is enabled, the architecture
>> requires a counter ID to read the event data.
>>
>> Introduce an is_cntr field in struct rmid_read to indicate whether counter
>> assignment mode is in use.
>>
>> Update the logic to call resctrl_arch_cntr_read() and
>> resctrl_arch_reset_cntr() when the assignment mode is active.
>>
>> Declare mbm_cntr_get() in fs/resctrl/internal.h to make it accessible to
>> other functions within fs/resctrl.
>>
>> Suggested-by: Reinette Chatre <reinette.chatre@intel.com>
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
>> v15: New patch to add is_cntr in rmid_read as discussed in
>>      https://lore.kernel.org/lkml/b4b14670-9cb0-4f65-abd5-39db996e8da9@intel.com/
>> ---
>>  fs/resctrl/ctrlmondata.c |  8 ++++++++
>>  fs/resctrl/internal.h    |  5 +++++
>>  fs/resctrl/monitor.c     | 42 +++++++++++++++++++++++++++++++++-------
>>  3 files changed, 48 insertions(+), 7 deletions(-)
>>
>> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
>> index ad7ffc6acf13..ce766b2cdfc1 100644
>> --- a/fs/resctrl/ctrlmondata.c
>> +++ b/fs/resctrl/ctrlmondata.c
>> @@ -569,6 +569,14 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>>  		return;
>>  	}
>>  
>> +	if (resctrl_arch_mbm_cntr_assign_enabled(r) && resctrl_is_mbm_event(evtid)) {
>> +		if (mbm_cntr_get(r, d, rdtgrp, evtid) < 0) {
>> +			rr->err = -ENOENT;
> 
> This introduces the new -ENOENT error code but rdtgroup_mondata_show() is not enabled to
> handle it. Looks like the next patch needs to be squashed into this one.

Sure.

> 
>> +			return;
> 
> Looking at this closer this does not seem the right place for this check. This is the
> top level mon_event_read() when the user reads an event file. If this is an event
> associated with a CTRL_MON group then resctrl should sum the data of the CTRL_MON group
> and all of its MON groups.
> It may be that the CTRL_MON group's event does not have a counter assigned, but one
> or more of the MON groups do. In this case I do not think resctrl should fail reading
> the CTRL_MON's event early as is done above but still provide the sum of the events that
> can be counted in the MON groups that do have counters assigned. With that, only return
> "Unassigned" if no counter is assigned in any CTRL_MON or MON group?

Yes. Very good point. Thanks

Changed the code to just set is_mbm_cntr here.
> 
> 
> There also appears to be potential for a leak here with the early exit without calling
> resctrl_arch_mon_ctx_free(). As mentioned earlier in series I do not think that
> arch_mon_ctx is relevant to this counter assignment so I think mbm_update_one_event()
> as well as mon_event_read() should make calling resctrl_arch_mon_ctx_alloc()
> conditional on is_cntr/is_mbm_cntr. 

Sure.

> 
> 
>> +		}
>> +		rr->is_cntr = true;
>> +	}
>> +
>>  	cpu = cpumask_any_housekeeping(cpumask, RESCTRL_PICK_ANY_CPU);
>>  
>>  	/*
>> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
>> index 647a0466ffa0..fb4fec4a4cdc 100644
>> --- a/fs/resctrl/internal.h
>> +++ b/fs/resctrl/internal.h
>> @@ -110,6 +110,8 @@ struct mon_data {
>>   *	   domains in @r sharing L3 @ci.id
>>   * @evtid: Which monitor event to read.
>>   * @first: Initialize MBM counter when true.
>> + * @is_cntr: Is the counter valid? true if "mbm_event" counter assignment mode is
>> + *	   enabled and it is an MBM event.
>>   * @ci_id: Cacheinfo id for L3. Only set when @d is NULL. Used when summing domains.
>>   * @err:   Error encountered when reading counter.
>>   * @val:   Returned value of event counter. If @rgrp is a parent resource group,
>> @@ -124,6 +126,7 @@ struct rmid_read {
>>  	struct rdt_mon_domain	*d;
>>  	enum resctrl_event_id	evtid;
>>  	bool			first;
>> +	bool			is_cntr;
> 
> After seeing how this all comes together the "is_cntr" is very generic and not
> matching the often used "mbm_cntr". What do you think of "is_mbm_cntr"?

Sure.

> 
>>  	unsigned int		ci_id;
>>  	int			err;
>>  	u64			val;
>> @@ -391,6 +394,8 @@ int rdtgroup_assign_cntr_event(struct rdt_mon_domain *d, struct rdtgroup *rdtgrp
>>  			       struct mon_evt *mevt);
>>  void rdtgroup_unassign_cntr_event(struct rdt_mon_domain *d, struct rdtgroup *rdtgrp,
>>  				  struct mon_evt *mevt);
>> +int mbm_cntr_get(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 73f507942b6d..35faca7ff3b1 100644
>> --- a/fs/resctrl/monitor.c
>> +++ b/fs/resctrl/monitor.c
>> @@ -366,9 +366,21 @@ static int __mon_event_count(struct rdtgroup *rdtgrp, struct rmid_read *rr)
>>  	struct mbm_state *m;
>>  	int err, ret;
>>  	u64 tval = 0;
>> +	int cntr_id;
> 
> I've tried a couple of checkers and not all can pick up that cntr_id is always
> assigned when it is used below. While it is not necessary it will be helpful to
> initialize cntr_id here (-ENOENT?) just to avoid needing to prove that hypothetical
> reports from these checkers are false positives.

Yes.

> 
>> +
>> +	if (rr->is_cntr) {
>> +		cntr_id = mbm_cntr_get(rr->r, rr->d, rdtgrp, rr->evtid);
>> +		if (cntr_id < 0) {
>> +			rr->err = -ENOENT;
>> +			return -EINVAL;
>> +		}
> 
> This looks to be the right place for the mbm_cntr_get() check. Just keeping this one
> avoids the duplication while also makeing the code match existing user ABI.
> What do you think?

That is perfect actually.

> 
>> +	}
>>  
>>  	if (rr->first) {
>> -		resctrl_arch_reset_rmid(rr->r, rr->d, closid, rmid, rr->evtid);
>> +		if (rr->is_cntr)
>> +			resctrl_arch_reset_cntr(rr->r, rr->d, closid, rmid, cntr_id, rr->evtid);
>> +		else
>> +			resctrl_arch_reset_rmid(rr->r, rr->d, closid, rmid, rr->evtid);
>>  		m = get_mbm_state(rr->d, closid, rmid, rr->evtid);
>>  		if (m)
>>  			memset(m, 0, sizeof(struct mbm_state));
>> @@ -379,8 +391,12 @@ static int __mon_event_count(struct rdtgroup *rdtgrp, struct rmid_read *rr)
>>  		/* Reading a single domain, must be on a CPU in that domain. */
>>  		if (!cpumask_test_cpu(cpu, &rr->d->hdr.cpu_mask))
>>  			return -EINVAL;
>> -		rr->err = resctrl_arch_rmid_read(rr->r, rr->d, closid, rmid,
>> -						 rr->evtid, &tval, rr->arch_mon_ctx);
>> +		if (rr->is_cntr)
>> +			rr->err = resctrl_arch_cntr_read(rr->r, rr->d, closid, rmid, cntr_id,
>> +							 rr->evtid, &tval, rr->arch_mon_ctx);
>> +		else
>> +			rr->err = resctrl_arch_rmid_read(rr->r, rr->d, closid, rmid,
>> +							 rr->evtid, &tval, rr->arch_mon_ctx);
>>  		if (rr->err)
>>  			return rr->err;
>>  
>> @@ -405,8 +421,12 @@ static int __mon_event_count(struct rdtgroup *rdtgrp, struct rmid_read *rr)
>>  	list_for_each_entry(d, &rr->r->mon_domains, hdr.list) {
>>  		if (d->ci_id != rr->ci_id)
>>  			continue;
>> -		err = resctrl_arch_rmid_read(rr->r, d, closid, rmid,
>> -					     rr->evtid, &tval, rr->arch_mon_ctx);
>> +		if (rr->is_cntr)
>> +			err = resctrl_arch_cntr_read(rr->r, d, closid, rmid, cntr_id,
>> +						     rr->evtid, &tval, rr->arch_mon_ctx);
>> +		else
>> +			err = resctrl_arch_rmid_read(rr->r, d, closid, rmid,
>> +						     rr->evtid, &tval, rr->arch_mon_ctx);
>>  		if (!err) {
>>  			rr->val += tval;
>>  			ret = 0;
>> @@ -620,6 +640,14 @@ static void mbm_update_one_event(struct rdt_resource *r, struct rdt_mon_domain *
>>  		return;
>>  	}
>>  
>> +	if (resctrl_arch_mbm_cntr_assign_enabled(r) && resctrl_is_mbm_event(evtid)) {
>> +		if (mbm_cntr_get(r, d, rdtgrp, evtid) < 0) {
>> +			rr.err = -ENOENT;
>> +			return;
>> +		}
> 
> This can be dropped also? Only is_cntr/is_mbm_cntr needs to be set here, __mon_event_count()
> called below duplicates above snippet and will set rr->err

Sure.

> 
> Same comment here about missing call to resctrl_arch_mon_ctx_free().

Sure.

> 
> 
>> +		rr.is_cntr = true;
>> +	}
>> +
>>  	__mon_event_count(rdtgrp, &rr);
>>  
>>  	/*
>> @@ -982,8 +1010,8 @@ static void resctrl_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d
>>   * 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 mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
>> +		 struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
>>  {
>>  	int cntr_id;
>>  
> 
> Reinette
> 

-- 
Thanks
Babu Moger