Re: [PATCH v16 20/34] fs/resctrl: Introduce counter ID read, reset calls in mbm_event mode

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

Hi Babu,

On 7/25/25 11:29 AM, Babu Moger wrote:
> When supported, "mbm_event" counter assignment mode allows users to assign
> a hardware counter to an RMID, event pair and monitor the bandwidth usage
> as long as it is assigned. The hardware continues to track the assigned
> counter until it is explicitly unassigned by the user.
> 
> Introduce the architecture calls resctrl_arch_cntr_read() and
> resctrl_arch_reset_cntr() to read and reset event counters when "mbm_event"
> mode is supported. Function names are chosen to match existing

(apologies if I gave you the text ... trying to polish with more focus on
imperative tone now)
"Function names are chosen to match" -> "Function names match"?

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

...

> ---
>  include/linux/resctrl.h | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 50e38445183a..4d37827121a6 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -613,6 +613,44 @@ void resctrl_arch_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
>  			      enum resctrl_event_id evtid, u32 rmid, u32 closid,
>  			      u32 cntr_id, bool assign);
>  
> +/**
> + * resctrl_arch_cntr_read() - Read the event data corresponding to the counter ID
> + *			      assigned to the RMID, event pair for this resource
> + *			      and domain.
> + * @r:			Resource that the counter should be read from.
> + * @d:			Domain that the counter should be read from.
> + * @closid:		CLOSID that matches the RMID.
> + * @rmid:		RMID used for counter ID assignment.

Can this be more specific, for example:
			The RMID to which @cntr_id is assigned.

> + * @cntr_id:		The counter ID whose event data should be read. Valid when
> + *			"mbm_event" mode is enabled and @eventid is MBM event.

Would the counter ID not always be valid? Specifically,  resctrl_arch_cntr_read() is
_only_ called when "mbm_event" mode is enabled and @eventid is _always_
an MBM event, no? If you agree, the @cntr_id description can be something like below
with the calling context details moved to general function description:

	 @cntr_id: The counter to read.

> + * @eventid:		eventid used for counter ID assignment, such as
> + *			QOS_L3_MBM_TOTAL_EVENT_ID or QOS_L3_MBM_LOCAL_EVENT_ID.

The "@eventid is an MBM event" can move here? For example:
			The MBM event to which @cntr_id is assigned.			

> + * @val:		Result of the counter read in bytes.
> + *

It looks to me as though some of the @cntr_id text could move to be the
function description. The description can also be expanded to include where this
will be called from. For example, 

	Called on a CPU that belongs to domain @d when "mbm_event" mode is enabled.
	Called from a non-migrateable process context via smp_call_on_cpu() unless
	all CPUs are nohz_full, in which case it is called via IPI (smp_call_function_any()).
	
The goal is to make information specific. Please feel free to improve.

> + * Return:
> + * 0 on success, or -EIO, -EINVAL etc on error.
> + */
> +int resctrl_arch_cntr_read(struct rdt_resource *r, struct rdt_mon_domain *d,
> +			   u32 closid, u32 rmid, int cntr_id,
> +			   enum resctrl_event_id eventid, u64 *val);
> +
> +/**
> + * resctrl_arch_reset_cntr() - Reset any private state associated with counter ID.
> + * @r:		The domain's resource.
> + * @d:		The counter ID's domain.
> + * @closid:	CLOSID that matches the RMID.
> + * @rmid:	RMID used for counter ID assignment.
> + * @cntr_id:	The counter ID whose event data should be reset. Valid when
> + *		"mbm_event" mode is enabled and @eventid is MBM event.
> + * @eventid:	eventid used for counter ID assignment, such as
> + *		QOS_L3_MBM_TOTAL_EVENT_ID or QOS_L3_MBM_LOCAL_EVENT_ID.

Above should similarly be specific.

> + *
> + * This can be called from any CPU.
> + */
> +void resctrl_arch_reset_cntr(struct rdt_resource *r, struct rdt_mon_domain *d,
> +			     u32 closid, u32 rmid, int cntr_id,
> +			     enum resctrl_event_id eventid);
> +
>  extern unsigned int resctrl_rmid_realloc_threshold;
>  extern unsigned int resctrl_rmid_realloc_limit;
>  

Reinette