Re: [PATCH RFC v3 06/15] arm_mpam: Support memory-level MSCs and ABMC per class

[Richard Cheng <icheng@nvidia.com>]

On Mon, Nov 09, 2026 at 01:24:18PM +0800, Fenghua Yu wrote:
> Some platforms place MBWU counters on a memory MSC above L3 while CSU
> occupancy may remain on the L3 cache MSC. The driver previously assumed
> all monitors and ABMC state lived on the L3 resource, which
> mis-associates MBA counters, breaks mbm_L3_assignments when multiple
> events share a class, and uses the wrong domain ID space for
> memory-level MSCs.
> 
> Teach MPAM resctrl to map monitor classes to L3 or MBA resources,
> initialise ABMC on the resource that owns the MBWU monitor, select the
> node-scope MBM total event for memory-side counters, and test
> mbm_cntr_assignable instead of inferring assignment support from
> whichever monitor happens to share res->class first.
> 
> Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
> Signed-off-by: Fenghua Yu <fenghuay@nvidia.com>
> ---
>  drivers/resctrl/mpam_resctrl.c | 112 ++++++++++++++++++++++++---------
>  1 file changed, 81 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
> index ca2ae4b5cc8a..47a7b18d841d 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -45,7 +45,7 @@ static struct mpam_resctrl_res mpam_resctrl_controls[RDT_NUM_RESOURCES];
>   * to those supported by MPAM.
>   * Class pointer may be NULL.
>   */
> -#define MPAM_MAX_EVENT QOS_L3_MBM_TOTAL_EVENT_ID
> +#define MPAM_MAX_EVENT QOS_NODE_MBM_TOTAL_EVENT_ID
>  static struct mpam_resctrl_mon mpam_resctrl_counters[MPAM_MAX_EVENT + 1];
>  
>  #define for_each_mpam_resctrl_mon(mon, eventid)					\
> @@ -88,6 +88,11 @@ bool resctrl_arch_alloc_capable(void)
>  	return false;
>  }
>  
> +static bool mpam_class_memory(struct mpam_class *class)
> +{
> +	return class && class->type == MPAM_CLASS_MEMORY && class->level > 3;
> +}
> +
>  bool resctrl_arch_mon_capable(void)
>  {
>  	struct mpam_resctrl_res *res = &mpam_resctrl_controls[RDT_RESOURCE_L3];
> @@ -121,7 +126,13 @@ void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_l3_mon_domain *d
>  
>  bool resctrl_arch_mbm_cntr_assign_enabled(struct rdt_resource *r)
>  {
> -	return (r == &mpam_resctrl_controls[RDT_RESOURCE_L3].resctrl_res);
> +	/*
> +	 * mbm_cntr_assignable is set only when ABMC is initialised on this
> +	 * resource. Multiple monitor events may share res->class (e.g.
> +	 * occupancy and MBWU), so assignment support must not be inferred
> +	 * from mon->assigned_counters via a class lookup on the wrong event.
> +	 */
> +	return r->mon.mbm_cntr_assignable;
>  }
>  
>  int resctrl_arch_mbm_cntr_assign_set(struct rdt_resource *r, bool enable)
> @@ -181,24 +192,41 @@ static void resctrl_reset_task_closids(void)
>  	read_unlock(&tasklist_lock);
>  }
>  
> -static void mpam_resctrl_monitor_sync_abmc_vals(struct rdt_resource *l3)
> +static struct
> +mpam_resctrl_res *mpam_resctrl_res_from_mon(struct mpam_resctrl_mon *mon)
>  {
> -	struct mpam_resctrl_mon *mon = &mpam_resctrl_counters[QOS_L3_MBM_TOTAL_EVENT_ID];
> +	struct mpam_resctrl_res *res;
> +	enum resctrl_res_level rid;
>  
>  	if (!mon->class)
> -		return;
> +		return NULL;
> +
> +	for_each_mpam_resctrl_control(res, rid) {
> +		if (res->class == mon->class)
> +			return res;
> +	}
> +
> +	return NULL;
> +}
> +
> +static struct mpam_resctrl_mon *mpam_resctrl_mbm_total_mon(void)
> +{
> +	if (mpam_resctrl_counters[QOS_NODE_MBM_TOTAL_EVENT_ID].class)
> +		return &mpam_resctrl_counters[QOS_NODE_MBM_TOTAL_EVENT_ID];
> +
> +	return &mpam_resctrl_counters[QOS_L3_MBM_TOTAL_EVENT_ID];
> +}
> +
> +static void mpam_resctrl_monitor_sync_abmc_vals(struct rdt_resource *r)
> +{
> +	struct mpam_resctrl_mon *mon = mpam_resctrl_mbm_total_mon();
>  
> -	if (!mon->assigned_counters)
> +	if (!mon->class || !mon->assigned_counters)
>  		return;
>  
> -	l3->mon.num_mbm_cntrs = mon->class->props.num_mbwu_mon;
> +	r->mon.num_mbm_cntrs = mon->class->props.num_mbwu_mon;
>  	if (cdp_enabled)
> -		l3->mon.num_mbm_cntrs /= 2;
> -
> -	/*
> -	 * Continue as normal even if enabling cdp causes there to be
> -	 * zero counters. This avoids giving resctrl mixed messages.
> -	 */
> +		r->mon.num_mbm_cntrs /= 2;
>  }
>  
>  int resctrl_arch_set_cdp_enabled(struct rdt_resource *r, struct resctrl_ctrl *ctrl,
> @@ -404,6 +432,7 @@ static int resctrl_arch_mon_ctx_alloc_no_wait(enum resctrl_event_id evtid)
>  		return mpam_alloc_csu_mon(mon->class);
>  	case QOS_L3_MBM_LOCAL_EVENT_ID:
>  	case QOS_L3_MBM_TOTAL_EVENT_ID:
> +	case QOS_NODE_MBM_TOTAL_EVENT_ID:
>  		return USE_PRE_ALLOCATED;
>  	default:
>  		return -EOPNOTSUPP;
> @@ -1160,7 +1189,10 @@ static void mpam_resctrl_pick_counters(void)
>  			 * and it's equivalent to mbm_total and so always use
>  			 * mbm_total.
>  			 */
> -			counter_update_class(QOS_L3_MBM_TOTAL_EVENT_ID, class);
> +			if (class->type == MPAM_CLASS_MEMORY)
> +				counter_update_class(QOS_NODE_MBM_TOTAL_EVENT_ID, class);
> +			else
> +				counter_update_class(QOS_L3_MBM_TOTAL_EVENT_ID, class);
>  		}
>  	}
>  }
> @@ -1187,7 +1219,7 @@ void resctrl_arch_config_cntr(struct rdt_resource *r, struct rdt_l3_mon_domain *
>  {
>  	struct mpam_resctrl_mon *mon = &mpam_resctrl_counters[evtid];
>  
> -	if (evtid != QOS_L3_MBM_TOTAL_EVENT_ID) {
> +	if (!resctrl_is_mbm_total_event(evtid)) {
>  		pr_debug("unexpected event id\n");
>  		return;
>  	}
> @@ -1204,7 +1236,7 @@ void resctrl_arch_config_cntr(struct rdt_resource *r, struct rdt_l3_mon_domain *
>  		__config_cntr(mon, cntr_id, CDP_NONE, closid, rmid, assign);
>  	}
>  
> -	resctrl_arch_reset_cntr(r, d, closid, rmid, cntr_id, QOS_L3_MBM_TOTAL_EVENT_ID);
> +	resctrl_arch_reset_cntr(r, d, closid, rmid, cntr_id, evtid);
>  }
>  
>  static int mpam_resctrl_control_init(struct mpam_resctrl_res *res)
> @@ -1303,10 +1335,10 @@ static int mpam_resctrl_pick_domain_id(int cpu, struct mpam_component *comp)
>   */
>  static int mpam_resctrl_monitor_init_abmc(struct mpam_resctrl_mon *mon)
>  {
> -	struct mpam_resctrl_res *res = &mpam_resctrl_controls[RDT_RESOURCE_L3];
>  	size_t num_rmid = resctrl_arch_system_num_rmid_idx();
> -	struct rdt_resource *l3 = &res->resctrl_res;
>  	struct mpam_class *class = mon->class;
> +	struct mpam_resctrl_res *res;
> +	struct rdt_resource *r;
>  	u16 num_mbwu_mon;
>  	int *cntrs;
>  
> @@ -1317,6 +1349,12 @@ static int mpam_resctrl_monitor_init_abmc(struct mpam_resctrl_mon *mon)
>  	}
>  	memset(rmid_array, -1, num_rmid * sizeof(*rmid_array));
>  
> +	res = mpam_resctrl_res_from_mon(mon);
> +	if (!res)
> +		return -EINVAL;
> +
> +	r = &res->resctrl_res;
> +
>  	num_mbwu_mon = class->props.num_mbwu_mon;
>  	cntrs = __alloc_mbwu_array(mon->class, num_mbwu_mon);
>  	if (IS_ERR(cntrs))
> @@ -1324,12 +1362,12 @@ static int mpam_resctrl_monitor_init_abmc(struct mpam_resctrl_mon *mon)
>  	mon->assigned_counters = cntrs;
>  	mon->mbwu_idx_to_mon = no_free_ptr(rmid_array);
>  
> -	l3->mon.mbm_cntr_assignable = true;
> -	l3->mon.mbm_assign_on_mkdir = true;
> -	l3->mon.mbm_cntr_configurable = false;
> -	l3->mon.mbm_cntr_assign_fixed = true;
> +	r->mon.mbm_cntr_assignable = true;
> +	r->mon.mbm_assign_on_mkdir = true;
> +	r->mon.mbm_cntr_configurable = false;
> +	r->mon.mbm_cntr_assign_fixed = true;
>  
> -	mpam_resctrl_monitor_sync_abmc_vals(l3);
> +	mpam_resctrl_monitor_sync_abmc_vals(r);
> 

Hi Fenghua,

Maybe update the call in resctrl_arch_set_cdp_enbled()?
It still calls mpam_resctrl_monitor_sync_abmc_vals(l3), so enabling CDP
doesn't halve the NODE/MBA counter capacity.

With 16 physical NODE counters, the allocator still allows logical counter 8.
Under CDP, that maps to assigned_counters[17], outside the 16-entry
array.

Best regards,
Richard Cheng.

 
>  	return 0;
>  }
> @@ -1337,8 +1375,15 @@ static int mpam_resctrl_monitor_init_abmc(struct mpam_resctrl_mon *mon)
>  static int mpam_resctrl_monitor_init(struct mpam_resctrl_mon *mon,
>  				     enum resctrl_event_id type)
>  {
> -	struct mpam_resctrl_res *res = &mpam_resctrl_controls[RDT_RESOURCE_L3];
> -	struct rdt_resource *l3 = &res->resctrl_res;
> +	struct mpam_resctrl_res *res;
> +	struct rdt_resource *r;
> +
> +	if (mpam_class_memory(mon->class))
> +		res = &mpam_resctrl_controls[RDT_RESOURCE_MBA];
> +	else
> +		res = &mpam_resctrl_controls[RDT_RESOURCE_L3];
> +
> +	r = &res->resctrl_res;
>  
>  	lockdep_assert_cpus_held();
>  
> @@ -1365,8 +1410,13 @@ static int mpam_resctrl_monitor_init(struct mpam_resctrl_mon *mon,
>  	 * monitoring class.
>  	 * Setting name is necessary on monitor only platforms.
>  	 */
> -	l3->name = "L3";
> -	l3->mon_scope = RESCTRL_L3_CACHE;
> +	if (mpam_class_memory(mon->class)) {
> +		r->name = "MB";
> +		r->mon_scope = RESCTRL_NODE;
> +	} else {
> +		r->name = "L3";
> +		r->mon_scope = RESCTRL_L3_CACHE;
> +	}
>  
>  	/*
>  	 * num-rmid is the upper bound for the number of monitoring groups that
> @@ -1376,9 +1426,9 @@ static int mpam_resctrl_monitor_init(struct mpam_resctrl_mon *mon,
>  	 * this does mean userspace needs to know the architecture to correctly
>  	 * interpret this value.
>  	 */
> -	l3->mon.num_rmid = resctrl_arch_system_num_rmid_idx();
> +	r->mon.num_rmid = resctrl_arch_system_num_rmid_idx();
>  
> -	if (type == QOS_L3_MBM_TOTAL_EVENT_ID) {
> +	if (type == QOS_L3_MBM_TOTAL_EVENT_ID || type == QOS_NODE_MBM_TOTAL_EVENT_ID) {
>  		int err;
>  
>  		err = mpam_resctrl_monitor_init_abmc(mon);
> @@ -1386,13 +1436,13 @@ static int mpam_resctrl_monitor_init(struct mpam_resctrl_mon *mon,
>  			return err;
>  
>  		static_assert(MAX_EVT_CONFIG_BITS == 0x7f);
> -		l3->mon.mbm_cfg_mask = MAX_EVT_CONFIG_BITS;
> +		r->mon.mbm_cfg_mask = MAX_EVT_CONFIG_BITS;
>  	}
>  
>  	if (!resctrl_enable_mon_event(type, false, 0, NULL))
>  		return -EINVAL;
>  
> -	l3->mon_capable = true;
> +	r->mon_capable = true;
>  
>  	return 0;
>  }
> -- 
> 2.53.0
>