Re: [PATCH v14 12/32] fs/resctrl: Introduce interface to display number of assignable counter IDs

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

Hi Reinette,

On 6/24/25 18:05, Reinette Chatre wrote:
> Hi Babu,
> 
> There seems to be many places referring to user space assigning "counter IDs",
> as I understand the interface the user has no control over the actual ID of the
> counter being assigned. Please correct me if I am wrong.

Yes. Agree. Users have no control over which counter is assigned.

> Considering this, how about:
> 	fs/resctrl: Add resctrl file to display number of assignable counters
> 
> If you agree, please check the whole series as this seems to be an often
> copy&pasted term.

Yes. Sure.

> 
> On 6/13/25 2:04 PM, Babu Moger wrote:
>> The "mbm_event" mode allows users to assign a hardware counter ID to an
> 
> "a hardware counter ID" -> "a hardware counter"?
> 
>> RMID, event pair and monitor bandwidth usage as long as it is assigned.
>> The hardware continues to track the assigned counter until it is
>> explicitly unassigned by the user.
>>
>> Create 'num_mbm_cntrs' resctrl file that displays the number of counter
>> IDs supported in each domain. 'num_mbm_cntrs' is only visible to user
> 
> "number of counter IDs" -> "number of counters"?
> 
>> space when the system supports "mbm_event" mode.
>>
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
> 
> ...
> 
>> ---
>>  Documentation/filesystems/resctrl.rst | 11 ++++++++++
>>  fs/resctrl/monitor.c                  |  4 ++++
>>  fs/resctrl/rdtgroup.c                 | 30 +++++++++++++++++++++++++++
>>  3 files changed, 45 insertions(+)
>>
>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>> index 4e76e4ac5d3a..801914de0c81 100644
>> --- a/Documentation/filesystems/resctrl.rst
>> +++ b/Documentation/filesystems/resctrl.rst
>> @@ -288,6 +288,17 @@ with the following files:
>>  	result in misleading values or display "Unavailable" if no counter is assigned
>>  	to the event.
>>  
>> +"num_mbm_cntrs":
>> +	The maximum number of counter IDs (total of available and assigned counters)
> 
> "number of counter IDs" -> "number of counters"

Sure.

> 
>> +	in each domain when the system supports mbm_event mode.
>> +
>> +	For example, on a system with maximum of 32 memory bandwidth monitoring
>> +	counters in each of its L3 domains:
>> +	::
>> +
>> +	  # cat /sys/fs/resctrl/info/L3_MON/num_mbm_cntrs
>> +	  0=32;1=32
>> +
>>  "max_threshold_occupancy":
>>  		Read/write file provides the largest value (in
>>  		bytes) at which a previously used LLC_occupancy
>> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
>> index dcc6c00eb362..92a87aa97b0f 100644
>> --- a/fs/resctrl/monitor.c
>> +++ b/fs/resctrl/monitor.c
>> @@ -924,6 +924,10 @@ int resctrl_mon_resource_init(void)
>>  	else if (resctrl_is_mon_event_enabled(QOS_L3_MBM_TOTAL_EVENT_ID))
>>  		mba_mbps_default_event = QOS_L3_MBM_TOTAL_EVENT_ID;
>>  
>> +	if (r->mon.mbm_cntr_assignable)
>> +		resctrl_file_fflags_init("num_mbm_cntrs",
>> +					 RFTYPE_MON_INFO | RFTYPE_RES_CACHE);
>> +
>>  	return 0;
>>  }
>>  
>> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
>> index ba7a9a68c5a6..967e4df62a19 100644
>> --- a/fs/resctrl/rdtgroup.c
>> +++ b/fs/resctrl/rdtgroup.c
>> @@ -1829,6 +1829,30 @@ static int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
>>  	return 0;
>>  }
>>  
>> +static int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
>> +				      struct seq_file *s, void *v)
>> +{
>> +	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
>> +	struct rdt_mon_domain *dom;
>> +	bool sep = false;
>> +
>> +	cpus_read_lock();
>> +	mutex_lock(&rdtgroup_mutex);
>> +
>> +	list_for_each_entry(dom, &r->mon_domains, hdr.list) {
>> +		if (sep)
>> +			seq_putc(s, ';');
>> +
>> +		seq_printf(s, "%d=%d", dom->hdr.id, r->mon.num_mbm_cntrs);
>> +		sep = true;
>> +	}
>> +	seq_putc(s, '\n');
>> +
>> +	mutex_unlock(&rdtgroup_mutex);
>> +	cpus_read_unlock();
>> +	return 0;
>> +}
>> +
>>  /* rdtgroup information files for one cache resource. */
>>  static struct rftype res_common_files[] = {
>>  	{
>> @@ -1866,6 +1890,12 @@ static struct rftype res_common_files[] = {
>>  		.seq_show	= rdt_default_ctrl_show,
>>  		.fflags		= RFTYPE_CTRL_INFO | RFTYPE_RES_CACHE,
>>  	},
>> +	{
>> +		.name		= "num_mbm_cntrs",
>> +		.mode		= 0444,
>> +		.kf_ops		= &rdtgroup_kf_single_ops,
>> +		.seq_show	= resctrl_num_mbm_cntrs_show,
>> +	},
>>  	{
>>  		.name		= "min_cbm_bits",
>>  		.mode		= 0444,
> 
> Patch looks good.
> 
> Reinette
> 

-- 
Thanks
Babu Moger