Re: [PATCH v16 23/34] fs/resctrl: Support counter read/reset with mbm_event assignment mode

[Reinette Chatre <reinette.chatre@intel.com>]

Hi Babu,

On 7/25/25 11:29 AM, 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_mbm_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. Report
> 'Unassigned' in case the user attempts to read the event without assigning
> a hardware counter.
> 
> Declare mbm_cntr_get() in fs/resctrl/internal.h to make it accessible to
> other functions within fs/resctrl.

From what I can tell this is not needed by this patch. It is also a hint that
there may be some monitoring specific code outside of monitor.c. Looks like this
is done to support later patch #29 "fs/resctrl: Introduce mbm_L3_assignments to
list assignments in a group" where mbm_L3_assignments_show() should rather
be in monitor.c

> 
> Suggested-by: Reinette Chatre <reinette.chatre@intel.com>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
...

> ---
>  Documentation/filesystems/resctrl.rst |  6 ++++
>  fs/resctrl/ctrlmondata.c              | 22 +++++++++---
>  fs/resctrl/internal.h                 |  5 +++
>  fs/resctrl/monitor.c                  | 52 ++++++++++++++++++++-------
>  4 files changed, 67 insertions(+), 18 deletions(-)
> 
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index 446736dbd97f..4c24c5f3f4c1 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -434,6 +434,12 @@ When monitoring is enabled all MON groups will also contain:
>  	for the L3 cache they occupy). These are named "mon_sub_L3_YY"
>  	where "YY" is the node number.
>  
> +	When the 'mbm_event' counter assignment mode is enabled, reading
> +	an MBM event of a MON group returns 'Unassigned' if no hardware
> +	counter is assigned to it. For CTRL_MON groups, 'Unassigned' is
> +	returned if the MBM event does not have an assigned counter in the
> +	CTRL_MON group nor in any of its associated MON groups.
> +
>  "mon_hw_id":
>  	Available only with debug option. The identifier used by hardware
>  	for the monitor group. On x86 this is the RMID.
> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
> index ad7ffc6acf13..31787ce6ec91 100644
> --- a/fs/resctrl/ctrlmondata.c
> +++ b/fs/resctrl/ctrlmondata.c
> @@ -563,10 +563,15 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>  	rr->r = r;
>  	rr->d = d;
>  	rr->first = first;
> -	rr->arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, evtid);
> -	if (IS_ERR(rr->arch_mon_ctx)) {
> -		rr->err = -EINVAL;
> -		return;
> +	if (resctrl_arch_mbm_cntr_assign_enabled(r) &&
> +	    resctrl_is_mbm_event(evtid)) {
> +		rr->is_mbm_cntr = true;
> +	} else {
> +		rr->arch_mon_ctx = resctrl_arch_mon_ctx_alloc(r, evtid);
> +		if (IS_ERR(rr->arch_mon_ctx)) {
> +			rr->err = -EINVAL;
> +			return;
> +		}
>  	}
>  
>  	cpu = cpumask_any_housekeeping(cpumask, RESCTRL_PICK_ANY_CPU);
> @@ -582,7 +587,8 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r,
>  	else
>  		smp_call_on_cpu(cpu, smp_mon_event_count, rr, false);
>  
> -	resctrl_arch_mon_ctx_free(r, evtid, rr->arch_mon_ctx);
> +	if (rr->arch_mon_ctx)
> +		resctrl_arch_mon_ctx_free(r, evtid, rr->arch_mon_ctx);
>  }
>  
>  int rdtgroup_mondata_show(struct seq_file *m, void *arg)
> @@ -653,10 +659,16 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
>  
>  checkresult:
>  
> +	/*
> +	 * -ENOENT is a special case, set only when "mbm_event" counter assignment
> +	 * mode is enabled and no counter has been assigned.
> +	 */
>  	if (rr.err == -EIO)
>  		seq_puts(m, "Error\n");
>  	else if (rr.err == -EINVAL)
>  		seq_puts(m, "Unavailable\n");
> +	else if (rr.err == -ENOENT)
> +		seq_puts(m, "Unassigned\n");
>  	else
>  		seq_printf(m, "%llu\n", rr.val);
>  
> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
> index 216588842444..eeee83a5067a 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_mbm_cntr: Is the counter valid? true if "mbm_event" counter assignment mode is
> + *	   enabled and it is an MBM event.

Since a counter may not be assigned to event being read I do not believe that "Is the counter
valid?" is accurate and should rather be dropped. Rest of text looks accurate to me.  

>   * @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_mbm_cntr;
>  	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);
>  

Not necessary? mbm_cntr_get() can remain internal to monitor.c

>  #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 070965d45770..a8b53b0ad0b7 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -362,13 +362,25 @@ static int __mon_event_count(struct rdtgroup *rdtgrp, struct rmid_read *rr)
>  	u32 closid = rdtgrp->closid;
>  	u32 rmid = rdtgrp->mon.rmid;
>  	struct rdt_mon_domain *d;
> +	int cntr_id = -ENOENT;
>  	struct cacheinfo *ci;
>  	struct mbm_state *m;
>  	int err, ret;
>  	u64 tval = 0;
>  
> +	if (rr->is_mbm_cntr) {
> +		cntr_id = mbm_cntr_get(rr->r, rr->d, rdtgrp, rr->evtid);
> +		if (cntr_id < 0) {
> +			rr->err = -ENOENT;
> +			return -EINVAL;
> +		}
> +	}
> +
>  	if (rr->first) {
> -		resctrl_arch_reset_rmid(rr->r, rr->d, closid, rmid, rr->evtid);
> +		if (rr->is_mbm_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_mbm_cntr)
> +			rr->err = resctrl_arch_cntr_read(rr->r, rr->d, closid, rmid, cntr_id,
> +							 rr->evtid, &tval);
> +		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_mbm_cntr)
> +			err = resctrl_arch_cntr_read(rr->r, d, closid, rmid, cntr_id,
> +						     rr->evtid, &tval);
> +		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;
> @@ -613,11 +633,16 @@ static void mbm_update_one_event(struct rdt_resource *r, struct rdt_mon_domain *
>  	rr.r = r;
>  	rr.d = d;
>  	rr.evtid = evtid;
> -	rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> -	if (IS_ERR(rr.arch_mon_ctx)) {
> -		pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> -				    PTR_ERR(rr.arch_mon_ctx));
> -		return;
> +	if (resctrl_arch_mbm_cntr_assign_enabled(r) &&
> +	    resctrl_arch_mbm_cntr_assign_enabled(r)) {

Duplicate check?

> +		rr.is_mbm_cntr = true;
> +	} else {
> +		rr.arch_mon_ctx = resctrl_arch_mon_ctx_alloc(rr.r, rr.evtid);
> +		if (IS_ERR(rr.arch_mon_ctx)) {
> +			pr_warn_ratelimited("Failed to allocate monitor context: %ld",
> +					    PTR_ERR(rr.arch_mon_ctx));
> +			return;
> +		}
>  	}
>  
>  	__mon_event_count(rdtgrp, &rr);
> @@ -629,7 +654,8 @@ static void mbm_update_one_event(struct rdt_resource *r, struct rdt_mon_domain *
>  	if (is_mba_sc(NULL))
>  		mbm_bw_count(rdtgrp, &rr);
>  
> -	resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
> +	if (rr.arch_mon_ctx)
> +		resctrl_arch_mon_ctx_free(rr.r, rr.evtid, rr.arch_mon_ctx);
>  }
>  
>  static void mbm_update(struct rdt_resource *r, struct rdt_mon_domain *d,
> @@ -983,8 +1009,8 @@ static void rdtgroup_assign_cntr(struct rdt_resource *r, struct rdt_mon_domain *
>   * 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;
>  

Not necessary?

Reinette