linux-kernel - Re: [PATCH v7 08/10] fs/resctrl: Introduce interface to display io

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Message-ID: <4efddbf1-1e98-4ee5-8057-7b3ce5adbec2@amd.com>
Date: Mon, 4 Aug 2025 13:14:36 -0500
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, corbet@....net,
 tony.luck@...el.com, Dave.Martin@....com, james.morse@....com,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, akpm@...ux-foundation.org,
 paulmck@...nel.org, rostedt@...dmis.org, Neeraj.Upadhyay@....com,
 david@...hat.com, arnd@...db.de, fvdl@...gle.com, seanjc@...gle.com,
 thomas.lendacky@....com, pawan.kumar.gupta@...ux.intel.com,
 yosry.ahmed@...ux.dev, sohil.mehta@...el.com, xin@...or.com,
 kai.huang@...el.com, xiaoyao.li@...el.com, peterz@...radead.org,
 me@...aill.net, mario.limonciello@....com, xin3.li@...el.com,
 ebiggers@...gle.com, ak@...ux.intel.com, chang.seok.bae@...el.com,
 andrew.cooper3@...rix.com, perry.yuan@....com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 08/10] fs/resctrl: Introduce interface to display
 io_alloc CBMs

Hi Reinette,

On 7/21/25 18:42, Reinette Chatre wrote:
> Hi Babu,
> 
> On 7/10/25 10:16 AM, Babu Moger wrote:
>> The io_alloc feature in resctrl enables system software to configure
>> the portion of the cache allocated for I/O traffic.
>>
>> Add "io_alloc_cbm" resctrl file to display CBMs (Capacity Bit Mask) o
>> fio_alloc feature.
> 
> "o fio_alloc" -> "of the io_alloc"
> 

Sure.

>>
>> The CBM interface file io_alloc_cbm will reside in the info directory
> 
> "will reside" -> "resides"
> 

Sure.

>> (e.g., /sys/fs/resctrl/info/L3/). Displaying the resource name is not
>> necessary. Pass the resource name to show_doms() and print it only if
>> the name is valid. For io_alloc, pass NULL to suppress printing the
>> resource name.
>>
>> When CDP is enabled, io_alloc routes traffic using the highest CLOSID
>> associated with an L3CODE resource. However, CBMs can be accessed via
>> either L3CODE or L3DATA resources.
> 
> Seems like something is missing here since this is motivation for a behavior
> but no mention of the behavior being motivated. Also please use imperative tone.

Sure. Added motivation for this.

> 
>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> 
> ...
> 
>> ---
>>  Documentation/filesystems/resctrl.rst | 18 +++++++++++
>>  fs/resctrl/ctrlmondata.c              |  8 +++--
>>  fs/resctrl/internal.h                 |  2 ++
>>  fs/resctrl/rdtgroup.c                 | 43 ++++++++++++++++++++++++++-
>>  4 files changed, 67 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>> index 189c1ccb92d6..c22a9dd667cd 100644
>> --- a/Documentation/filesystems/resctrl.rst
>> +++ b/Documentation/filesystems/resctrl.rst
>> @@ -176,6 +176,24 @@ related to allocation:
>>  		When CDP is enabled, io_alloc routes I/O traffic using the highest
>>  		CLOSID allocated for the instruction cache (L3CODE).
>>  
>> +"io_alloc_cbm":
>> +		CBMs(Capacity Bit Masks) that describe the portions of cache instances
>> +		to which I/O traffic from supported I/O devices are routed.
> 
> "are routed" -> "are routed when "io_alloc" is enabled"?
> 

Sure.

>> +
>> +		CBMs are displayed in the following format:
>> +
>> +			<cache_id0>=<cbm>;<cache_id1>=<cbm>;...
>> +
>> +		Example::
>> +
>> +			# cat /sys/fs/resctrl/info/L3/io_alloc_cbm
>> +			0=ffff;1=ffff
>> +
>> +		When CDP is enabled "io_alloc_cbm" associated with the DATA and CODE
>> +		resources may reflect the same values. For example, values read from and
>> +		written to /sys/fs/resctrl/info/L3DATA/io_alloc_cbm may be reflected by
>> +		/sys/fs/resctrl/info/L3CODE/io_alloc_cbm and vice versa.
>> +
>>  Memory bandwidth(MB) subdirectory contains the following files
>>  with respect to allocation:
>>  
>> diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
>> index d98e0d2de09f..e78828b0408a 100644
>> --- a/fs/resctrl/ctrlmondata.c
>> +++ b/fs/resctrl/ctrlmondata.c
>> @@ -381,7 +381,8 @@ ssize_t rdtgroup_schemata_write(struct kernfs_open_file *of,
>>  	return ret ?: nbytes;
>>  }
>>  
>> -static void show_doms(struct seq_file *s, struct resctrl_schema *schema, int closid)
>> +void show_doms(struct seq_file *s, struct resctrl_schema *schema, char *resource_name,
> 
> show_doms() can remain static within ctrlmondata.c by moving resctrl_io_alloc_cbm_show()
> to ctrlmondata.c
> 

Yes. Moved it to ctrlmondata.c.
Thanks
Babu Moger