Message-ID: <bc29115c-c120-4911-9ac2-4d70838c4188@amd.com>
Date: Thu, 7 Aug 2025 14:59:43 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 tony.luck@...el.com, james.morse@....com, tglx@...utronix.de,
 mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com
Cc: Dave.Martin@....com, x86@...nel.org, hpa@...or.com,
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 Neeraj.Upadhyay@....com, david@...hat.com, arnd@...db.de, fvdl@...gle.com,
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 gautham.shenoy@....com, chang.seok.bae@...el.com, linux-doc@...r.kernel.org,
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Subject: Re: [PATCH v16 20/34] fs/resctrl: Introduce counter ID read, reset
 calls in mbm_event mode

Hi Reinette,

On 7/30/25 14:59, Reinette Chatre wrote:
> 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"?

Looks good.

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

Sure.

> 
>> + * @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.

Yes. that is fine.

> 
>> + * @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.	

Sure.
		
> 
>> + * @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.

Looks good.

> 
>> + * 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.
> 

Sure.

>> + *
>> + * 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
> 

-- 
Thanks
Babu Moger

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