Re: [PATCH v12 14/26] x86/resctrl: Add the functionality to assign MBM events

[Reinette Chatre]

Hi Babu,

On 4/15/25 7:20 AM, Moger, Babu wrote:
> Hi Reinette,
> 
> On 4/11/25 16:04, Reinette Chatre wrote:
>> Hi Babu,
>>
>> On 4/3/25 5:18 PM, Babu Moger wrote:
>>> The mbm_cntr_assign mode offers "num_mbm_cntrs" number of counters that
>>> can be assigned to an RMID, event pair and monitor the bandwidth as long
>>> as it is assigned.
>>
>> Above makes it sound as though multiple counters can be assigned to
>> an RMID, event pair.
>>
> 
> Yes. Multiple counter-ids can be assigned to RMID, event pair.

oh, are you referring to the assignments of different counters across multiple
domains?

> 
>>>
>>> Add the functionality to allocate and assign the counters to RMID, event
>>> pair in the domain.
>>
>> "assign *a* counter to an RMID, event pair"?
> 
> Sure.
> 
>>
>>>
>>> If all the counters are in use, the 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@xxxxxxx>
>>> ---
>>
>> ...
>>
>>> ---
>>>  arch/x86/kernel/cpu/resctrl/internal.h |   2 +
>>>  arch/x86/kernel/cpu/resctrl/monitor.c  | 124 +++++++++++++++++++++++++
>>>  2 files changed, 126 insertions(+)
>>>
>>> diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
>>> index 0b73ec451d2c..1a8ac511241a 100644
>>> --- a/arch/x86/kernel/cpu/resctrl/internal.h
>>> +++ b/arch/x86/kernel/cpu/resctrl/internal.h
>>> @@ -574,6 +574,8 @@ bool closid_allocated(unsigned int closid);
>>>  int resctrl_find_cleanest_closid(void);
>>>  void arch_mbm_evt_config_init(struct rdt_hw_mon_domain *hw_dom);
>>>  unsigned int mon_event_config_index_get(u32 evtid);
>>> +int resctrl_assign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
>>> +			      struct rdtgroup *rdtgrp, enum resctrl_event_id evtid, u32 evt_cfg);
>>
>> This is internal to resctrl fs. Why is it needed to provide both the event id
>> and the event configuration? Event configuration can be determined from event ID?
> 
> Yes. It can be done. Then I have to export the functions like
> mbm_get_assign_config() into monitor.c. To avoid that I passed it from
> here which I felt much more cleaner.

>From what I can tell, for example by looking at patch #22, callers of
resctrl_assign_cntr_event() now need to call mbm_get_assign_config()
every time before calling resctrl_assign_cntr_event(). Calling
mbm_get_assign_config() from within resctrl_assign_cntr_event() seems
simpler to me and that may result in mbm_get_assign_config() moving to 
monitor.c as an extra benefit.

...

>>> +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;
>>> +
>>> +	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;
>>> +}
>>> +
>>> +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;
>>> +}
>>> +
>>> +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));
>>> +}
>>> +
>>> +/*
>>> + * Allocate a fresh counter and configure the event if not assigned already.
>>> + */
>>> +static int resctrl_alloc_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
>>> +				     struct rdtgroup *rdtgrp, enum resctrl_event_id evtid,
>>> +				     u32 evt_cfg)
>>
>> Same here, why are both evtid and evt_cfg provided as arguments? 
> 
> Yes. It can be done. Then I have to export the functions like
> mbm_get_assign_config() into monitor.c. To avoid that I passed it from
> here which I felt much more cleaner.

Maybe even resctrl_assign_cntr_event() does not need to call mbm_get_assign_config()
but only resctrl_alloc_config_cntr() needs to call mbm_get_assign_config(). Doing so
may avoid more burden on callers while reducing parameters needed throughout.

Reinette