When supported "mbm_event" mode offers "num_mbm_cntrs" number of counters
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@amd.com>
---
v14: Updated the changelog little bit.
     Updated the code documentation for mbm_cntr_alloc() and  mbm_cntr_get().
     Passed struct mon_evt to resctrl_assign_cntr_event() that way to avoid
     back and forth calls to get event details.
     Updated the code documentation about the failure when counters are exhasted.
     Changed subject line to fs/resctrl.

v13: Updated changelog.
     Changed resctrl_arch_config_cntr() to return void instead of int.
     Just passing evtid is to resctrl_alloc_config_cntr() and
     resctrl_assign_cntr_event(). Event configuration value can be easily
     obtained from mon_evt list.
     Introduced new function mbm_get_mon_event() to get event configuration value.
     Added prototype descriptions to mbm_cntr_get() and mbm_cntr_alloc().
     Resolved conflicts caused by the recent FS/ARCH code restructure.
     The files monitor.c/rdtgroup.c have been split between FS and ARCH directories.

v12: Fixed typo in the subjest line.
     Replaced several counters with "num_mbm_cntrs" counters.
     Changed the check in resctrl_alloc_config_cntr() to reduce the indentation.
     Fixed the handling error on first failure.
     Added domain id and event id on failure.
     Fixed the return error override.
     Added new parameter event configuration (evt_cfg) to get the event configuration
     from user space.

v11: Patch changed again quite a bit.
     Moved the functions to monitor.c.
     Renamed rdtgroup_assign_cntr_event() to resctrl_assign_cntr_event().
     Refactored the resctrl_assign_cntr_event().
     Added functionality to exit on the first error during assignment.
     Simplified mbm_cntr_free().
     Removed the function mbm_cntr_assigned(). Will be using mbm_cntr_get() to
     figure out if the counter is assigned or not.
     Updated commit message and code comments.

v10: Patch changed completely.
     Counters are managed at the domain based on the discussion.
     https://lore.kernel.org/lkml/CALPaoCj+zWq1vkHVbXYP0znJbe6Ke3PXPWjtri5AFgD9cQDCUg@mail.gmail.com/
     Reset non-architectural MBM state.
     Commit message update.

v9: Introduced new function resctrl_config_cntr to assign the counter, update
    the bitmap and reset the architectural state.
    Taken care of error handling(freeing the counter) when assignment fails.
    Moved mbm_cntr_assigned_to_domain here as it used in this patch.
    Minor text changes.

v8: Renamed rdtgroup_assign_cntr() to rdtgroup_assign_cntr_event().
    Added the code to return the error if rdtgroup_assign_cntr_event fails.
    Moved definition of MBM_EVENT_ARRAY_INDEX to resctrl/internal.h.
    Updated typo in the comments.

v7: New patch. Moved all the FS code here.
    Merged rdtgroup_assign_cntr and rdtgroup_alloc_cntr.
    Adde new #define MBM_EVENT_ARRAY_INDEX.
---
 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.
+ */
+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)
+{
+	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));
+}
+
+/**
+ * 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;
+
+	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.
+ *
+ * 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.
+ */
+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.
+	 */
+	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.
+ */
+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;
+}
-- 
2.34.1

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 ..."?

> 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@amd.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 /**. 

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

> + */
> +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).

> +}
> +
> +/**
> + * 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.

> +	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"

> + *

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.

> + * 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"

> + */
> +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?

> +	 */
> +	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"

> + */
> +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

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@amd.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