linux-kernel - Re: [PATCH v3 26/26] x86/resctrl: Update Documentation for package events

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Message-ID: <8256d312-ba54-4fec-9a0a-db7d7f461a3f@intel.com>
Date: Fri, 18 Apr 2025 22:40:27 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghuay@...dia.com>, "Maciej
 Wieczor-Retman" <maciej.wieczor-retman@...el.com>, Peter Newman
	<peternewman@...gle.com>, James Morse <james.morse@....com>, Babu Moger
	<babu.moger@....com>, Drew Fustini <dfustini@...libre.com>, Dave Martin
	<Dave.Martin@....com>, Anil Keshavamurthy <anil.s.keshavamurthy@...el.com>
CC: <linux-kernel@...r.kernel.org>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v3 26/26] x86/resctrl: Update Documentation for package
 events

Hi Tony,

On 4/7/25 4:40 PM, Tony Luck wrote:
> Each "mon_data" directory is now divided between L3 events and package
> events.
> 
> The "info/PERF_PKG_MON" directory contains parameters for perf events.
> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  Documentation/filesystems/resctrl.rst | 38 ++++++++++++++++++++-------
>  1 file changed, 28 insertions(+), 10 deletions(-)
> 
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index 6768fc1fad16..b89a188b0321 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -167,7 +167,7 @@ with respect to allocation:
>  			bandwidth percentages are directly applied to
>  			the threads running on the core
>  
> -If RDT monitoring is available there will be an "L3_MON" directory
> +If RDT L3 monitoring is available there will be an "L3_MON" directory

I think "RDT" can just be dropped.

>  with the following files:
>  
>  "num_rmids":
> @@ -261,6 +261,17 @@ with the following files:
>  		bytes) at which a previously used LLC_occupancy
>  		counter can be considered for re-use.
>  
> +If RDT PERF monitoring is available there will be an "L3_PERF_PKG" directory

"L3_PERF_PKG" -> "PERF_PKG_MON" ?

I understand that the existing L3 documentation contains this term but I do not
see a reason why the documentation should make this new monitoring Intel/RDT specific.

Also, I do not think user can be expected to know what "perf monitoring" is.

> +with the following files:
> +
> +"num_rmids":
> +		The guaranteed number of hardware countes supporting RMIDs.

countes -> counters?

The use of "hardware counters" is a bit unexpected ... the series did not mention
this or I must have missed this.

> +		If more "CTRL_MON" + "MON" groups than this number are created,
> +		the system may report that counters are "unavailable" when read.

To be precise it is "Unavailable" ... but I do not think that is a good interface.

> +
> +"mon_features":
> +		Lists the perf monitoring events that are enabled on this system.

"PERF" (all caps) at top and "perf" lower case here?

> +
>  Finally, in the top level of the "info" directory there is a file
>  named "last_cmd_status". This is reset with every "command" issued
>  via the file system (making new directories or writing to any of the
> @@ -366,15 +377,22 @@ When control is enabled all CTRL_MON groups will also contain:
>  When monitoring is enabled all MON groups will also contain:
>  
>  "mon_data":
> -	This contains a set of files organized by L3 domain and by
> -	RDT event. E.g. on a system with two L3 domains there will
> -	be subdirectories "mon_L3_00" and "mon_L3_01".	Each of these
> -	directories have one file per event (e.g. "llc_occupancy",
> -	"mbm_total_bytes", and "mbm_local_bytes"). In a MON group these
> -	files provide a read out of the current value of the event for
> -	all tasks in the group. In CTRL_MON groups these files provide
> -	the sum for all tasks in the CTRL_MON group and all tasks in
> -	MON groups. Please see example section for more details on usage.
> +	This contains a set of directories, one for each instance
> +	of an L3 cache, or of a processor package. The L3 cache
> +	directories are named "mon_L3_00", "mon_L3_01" etc. The
> +	package directories "mon_PERF_PKG_00", "mon_PERF_PKG_01" etc.
> +
> +	Within each directory there is one file per event. In
> +	the L3 directories: "llc_occupancy", "mbm_total_bytes",
> +	and "mbm_local_bytes".	In the PERF_PKG directories: "core_energy",

stray tab here

> +	"activity", etc.
> +
> +	In a MON group these files provide a read out of the current
> +	value of the event for all tasks in the group. In CTRL_MON groups
> +	these files provide the sum for all tasks in the CTRL_MON group
> +	and all tasks in MON groups. Please see example section for more
> +	details on usage.
> +
>  	On systems with Sub-NUMA Cluster (SNC) enabled there are extra
>  	directories for each node (located within the "mon_L3_XX" directory
>  	for the L3 cache they occupy). These are named "mon_sub_L3_YY"

Reinette