Re: [PATCH v14 31/32] fs/resctrl: Introduce the interface to switch between monitor modes

[Moger, Babu]

Hi Reinette,

On 6/25/25 18:40, Reinette Chatre wrote:
> Hi Babu,
> 
> On 6/13/25 2:05 PM, Babu Moger wrote:
>> Resctrl subsystem can support two monitoring modes, "mbm_event" or
>> "default". In mbm_event mode, monitoring event can only accumulate data
>> while it is backed by a hardware counter. In "default" mode, resctrl
>> assumes there is a hardware counter for each event within every CTRL_MON
>> and MON group.
>>
>> Introduce interface to switch between mbm_event and default modes.
> 
> "Introduce interface" -> "Introduce mbm_assign_mode resctrl file"
> 
Sure.

>>
>> Example:
>> To list the MBM monitor modes supported:
>> $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> [mbm_event]
>> default
>>
>> To enable the "mbm_event" monitoring mode:
>> $ echo "mbm_event" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>>
>> To enable the "default" monitoring mode:
>> $ echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>>
>> MBM event counters are automatically reset as part of changing the mode.
>> Clear both architectural and non-architectural event states to prevent
>> overflow conditions during the next event read. Also clear assignable
>> counter configuration on all the domains.
>>
>> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
>> ---
> 
> ...
> 
>> ---
>>  Documentation/filesystems/resctrl.rst | 23 +++++++-
>>  fs/resctrl/internal.h                 |  2 +
>>  fs/resctrl/monitor.c                  | 27 ++++++++++
>>  fs/resctrl/rdtgroup.c                 | 78 +++++++++++++++++++++++++--
>>  4 files changed, 126 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>> index cd82c2966ed7..7e62c7fdcefa 100644
>> --- a/Documentation/filesystems/resctrl.rst
>> +++ b/Documentation/filesystems/resctrl.rst
>> @@ -259,7 +259,9 @@ with the following files:
>>  
>>  "mbm_assign_mode":
>>  	The supported monitoring modes. The enclosed brackets indicate which mode
>> -	is enabled.
>> +	is enabled. The MBM events (mbm_total_bytes and/or mbm_local_bytes) associated
> 
> Since there may be more events in future I think the "(mbm_total_bytes and/or
> mbm_local_bytes)" can be dropped.

Sure.

> 
>> +	with counters may reset when "mbm_assign_mode" is changed.
>> +
>>  	::
>>  
>>  	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> @@ -279,6 +281,15 @@ with the following files:
>>  	of counters available is described in the "num_mbm_cntrs" file. Changing the
>>  	mode may cause all counters on the resource to reset.
>>  
>> +	Moving to mbm_event mode require users to assign the counters to the events.
> 
> "Moving to mbm_event mode require" -> "mbm_event counter assignment mode requires"

Sure.

> 
>> +	Otherwise, the MBM event counters will return 'Unassigned' when read.
>> +
>> +	The mode is beneficial for AMD platforms that support more CTRL_MON
>> +	and MON groups than available hardware counters. By default, this
>> +	feature is enabled on AMD platforms with the ABMC (Assignable Bandwidth
>> +	Monitoring Counters) capability, ensuring counters remain assigned even
>> +	when the corresponding RMID is not actively used by any processor.
>> +
>>  	"default":
>>  
>>  	In default mode, resctrl assumes there is a hardware counter for each
>> @@ -288,6 +299,16 @@ with the following files:
>>  	result in misleading values or display "Unavailable" if no counter is assigned
>>  	to the event.
>>  
>> +	* To enable "mbm_event" monitoring mode:
>> +	  ::
>> +
>> +	    # echo "mbm_event" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +
>> +	* To enable "default" monitoring mode:
>> +	  ::
>> +
>> +	    # echo "default" > /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
>> +
>>  "num_mbm_cntrs":
>>  	The maximum number of counter IDs (total of available and assigned counters)
>>  	in each domain when the system supports mbm_event mode.
>> diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
>> index 14d99c723ea5..adc9ff3efdfd 100644
>> --- a/fs/resctrl/internal.h
>> +++ b/fs/resctrl/internal.h
>> @@ -414,6 +414,8 @@ void resctrl_unassign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *
>>  				 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);
>> +void resctrl_reset_rmid_all(struct rdt_resource *r, struct rdt_mon_domain *d);
>> +void mbm_cntr_free_all(struct rdt_resource *r, struct rdt_mon_domain *d);
>>  
>>  #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 618c94cd1ad8..504b869570e6 100644
>> --- a/fs/resctrl/monitor.c
>> +++ b/fs/resctrl/monitor.c
>> @@ -1045,6 +1045,33 @@ static void mbm_cntr_free(struct rdt_mon_domain *d, int cntr_id)
>>  	memset(&d->cntr_cfg[cntr_id], 0, sizeof(struct mbm_cntr_cfg));
>>  }
>>  
>> +/**
>> + * mbm_cntr_free_all() - Clear all the counter ID configuration details in the
>> + *			 domain @d. Called when mbm_assign_mode is changed.
>> + */
>> +void mbm_cntr_free_all(struct rdt_resource *r, struct rdt_mon_domain *d)
>> +{
>> +	memset(d->cntr_cfg, 0, sizeof(*d->cntr_cfg) * r->mon.num_mbm_cntrs);
>> +}
>> +
>> +/**
>> + * resctrl_reset_rmid_all() - Reset all non-architecture states for all the
>> + *			      supported RMIDs.
>> + */
>> +void resctrl_reset_rmid_all(struct rdt_resource *r, struct rdt_mon_domain *d)
> 
> struct rdt_resource *r is unused? At this time it seems unnecessary to check if
> an MBM event belongs to particular resource since at this point I expect only L3
> is possible. Even so, to be consistent and robust I think it would make flows
> easier to understand by always ensureing that mon_evt::rid matches
> expected resource.

Agree. But in this we dont access mon_evt structure here.

> 
>> +{
>> +	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>> +	enum resctrl_event_id evt;
>> +	int idx;
>> +
>> +	for_each_mbm_event_id(evt) {
>> +		if (!resctrl_is_mon_event_enabled(evt))
>> +			continue;
>> +		idx = MBM_STATE_IDX(evt);
>> +		memset(d->mbm_states[idx], 0, sizeof(struct mbm_state) * idx_limit);
> 
> sizeof(*d->mbm_states[0])?
> 

Sure.

>> +	}
>> +}
>> +
>>  /**
>>   * 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.
>> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
>> index 8c67e0897f25..6bb61fcf8673 100644
>> --- a/fs/resctrl/rdtgroup.c
>> +++ b/fs/resctrl/rdtgroup.c
>> @@ -1876,6 +1876,77 @@ static int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
>>  	return 0;
>>  }
>>  
>> +static ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of,
>> +					     char *buf, size_t nbytes, loff_t off)
>> +{
>> +	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
>> +	struct rdt_mon_domain *d;
>> +	int ret = 0;
>> +	bool enable;
>> +
>> +	/* Valid input requires a trailing newline */
>> +	if (nbytes == 0 || buf[nbytes - 1] != '\n')
>> +		return -EINVAL;
>> +
>> +	buf[nbytes - 1] = '\0';
>> +
>> +	cpus_read_lock();
>> +	mutex_lock(&rdtgroup_mutex);
>> +
>> +	rdt_last_cmd_clear();
>> +
>> +	if (!strcmp(buf, "default")) {
>> +		enable = 0;
>> +	} else if (!strcmp(buf, "mbm_event")) {
>> +		if (r->mon.mbm_cntr_assignable) {
>> +			enable = 1;
>> +		} else {
>> +			ret = -EINVAL;
>> +			rdt_last_cmd_puts("mbm_event mode is not supported\n");
>> +			goto write_exit;
> 
> write_exit -> out_unlock
> 

Sure.


>> +		}
>> +	} else {
>> +		ret = -EINVAL;
>> +		rdt_last_cmd_puts("Unsupported assign mode\n");
>> +		goto write_exit;
>> +	}
>> +
>> +	if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
>> +		ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
>> +		if (ret)
>> +			goto write_exit;
>> +
>> +		/* Update the visibility of BMEC related files */
>> +		resctrl_bmec_files_show(r, !enable);
>> +
>> +		/*
>> +		 * Initialize the default memory transaction values for
>> +		 * total and local events.
>> +		 */
>> +		if (resctrl_is_mon_event_enabled(QOS_L3_MBM_TOTAL_EVENT_ID))
>> +			resctrl_set_mon_evt_cfg(QOS_L3_MBM_TOTAL_EVENT_ID,
>> +						MAX_EVT_CONFIG_BITS);
>> +		if (resctrl_is_mon_event_enabled(QOS_L3_MBM_LOCAL_EVENT_ID))
>> +			resctrl_set_mon_evt_cfg(QOS_L3_MBM_LOCAL_EVENT_ID,
>> +						READS_TO_LOCAL_MEM |
>> +						READS_TO_LOCAL_S_MEM |
>> +						NON_TEMP_WRITE_TO_LOCAL_MEM);
> 
> Nice, yes, this belongs in resctrl fs.
> 
>> +		/*
>> +		 * Reset all the non-achitectural RMID state and assignable counters.
>> +		 */
>> +		list_for_each_entry(d, &r->mon_domains, hdr.list) {
>> +			mbm_cntr_free_all(r, d);
>> +			resctrl_reset_rmid_all(r, d);
>> +		}
>> +	}
>> +
>> +write_exit:
>> +	mutex_unlock(&rdtgroup_mutex);
>> +	cpus_read_unlock();
>> +
>> +	return ret ?: nbytes;
>> +}
>> +
>>  static int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
>>  				      struct seq_file *s, void *v)
>>  {
>> @@ -2203,8 +2274,8 @@ static int resctrl_process_assign(struct rdt_resource *r, struct rdtgroup *rdtgr
>>  	struct mon_evt *mevt;
>>  	int assign_state;
>>  	char domain[10];
>> +	int ret = 0;
>>  	bool found;
>> -	int ret;
>>  
>>  	mevt = mbm_get_mon_event_by_name(r, event);
>>  	if (!mevt) {
>> @@ -2249,7 +2320,7 @@ static int resctrl_process_assign(struct rdt_resource *r, struct rdtgroup *rdtgr
>>  
>>  	switch (assign_state) {
>>  	case ASSIGN_NONE:
>> -		ret = resctrl_unassign_cntr_event(r, d, rdtgrp, mevt);
>> +		resctrl_unassign_cntr_event(r, d, rdtgrp, mevt);
>>  		break;
>>  	case ASSIGN_EXCLUSIVE:
>>  		ret = resctrl_assign_cntr_event(r, d, rdtgrp, mevt);
> 
> Two stray hunks?
> 

Yes. Fixed it.


>> @@ -2463,9 +2534,10 @@ static struct rftype res_common_files[] = {
>>  	},
>>  	{
>>  		.name		= "mbm_assign_mode",
>> -		.mode		= 0444,
>> +		.mode		= 0644,
>>  		.kf_ops		= &rdtgroup_kf_single_ops,
>>  		.seq_show	= resctrl_mbm_assign_mode_show,
>> +		.write		= resctrl_mbm_assign_mode_write,
>>  		.fflags		= RFTYPE_MON_INFO | RFTYPE_RES_CACHE,
>>  	},
>>  	{
> 
> Reinette
> 

-- 
Thanks
Babu Moger