linux-kernel - Re: [PATCH v9 10/10] fs/resctrl: Update bit_usage to reflect io

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Message-ID: <fe8138c4-e9a0-4df7-988b-f31d75201280@amd.com>
Date: Fri, 19 Sep 2025 16:05:42 -0500
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 Babu Moger <babu.moger@....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, kas@...nel.org,
 rick.p.edgecombe@...el.com, akpm@...ux-foundation.org, paulmck@...nel.org,
 pmladek@...e.com, pawan.kumar.gupta@...ux.intel.com, rostedt@...dmis.org,
 kees@...nel.org, arnd@...db.de, fvdl@...gle.com, seanjc@...gle.com,
 thomas.lendacky@....com, manali.shukla@....com, perry.yuan@....com,
 sohil.mehta@...el.com, xin@...or.com, peterz@...radead.org,
 mario.limonciello@....com, gautham.shenoy@....com, nikunj@....com,
 dapeng1.mi@...ux.intel.com, ak@...ux.intel.com, chang.seok.bae@...el.com,
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 linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev, kvm@...r.kernel.org
Subject: Re: [PATCH v9 10/10] fs/resctrl: Update bit_usage to reflect io_alloc

Hi Reinette,

On 9/18/2025 1:08 AM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 9/2/25 3:41 PM, Babu Moger wrote:
>> When the io_alloc feature is enabled, a portion of the cache can be
>> configured for shared use between hardware and software.
> 
> (repetitive)
> 
>>
>> Update bit_usage representation to reflect the io_alloc configuration.
>> Revise the documentation for "shareable_bits" and "bit_usage" to reflect
>> the impact of io_alloc feature.
> 
> Attempt at new version, please feel free to improve:
> 
> 	The "shareable_bits" and "bit_usage" resctrl files associated with cache
> 	resources give insight into how instances of a cache is used.
>                                                                                  
> 	Update the annotated capacity bitmasks displayed by "bit_usage" to include the
> 	cache portions allocated for I/O via the "io_alloc" feature. "shareable_bits" is
> 	a global bitmask of shareable cache with I/O and can thus not present the
> 	per-domain I/O allocations possible with the "io_alloc" feature. Revise the
> 	"shareable_bits" documentation to direct users to "bit_usage" for accurate
> 	cache usage information.
> 

Looks good. Thanks

>>
>> Signed-off-by: Babu Moger <babu.moger@....com>
>> ---
> 
> ...
> 
>> ---
>>   Documentation/filesystems/resctrl.rst | 35 ++++++++++++++++-----------
>>   fs/resctrl/ctrlmondata.c              |  2 +-
>>   fs/resctrl/internal.h                 |  2 ++
>>   fs/resctrl/rdtgroup.c                 | 21 ++++++++++++++--
>>   4 files changed, 43 insertions(+), 17 deletions(-)
>>
>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>> index 7e3eda324de5..72ea6f3f36bc 100644
>> --- a/Documentation/filesystems/resctrl.rst
>> +++ b/Documentation/filesystems/resctrl.rst
>> @@ -90,12 +90,19 @@ related to allocation:
>>   		must be set when writing a mask.
>>   
>>   "shareable_bits":
>> -		Bitmask of shareable resource with other executing
>> -		entities (e.g. I/O). User can use this when
>> -		setting up exclusive cache partitions. Note that
>> -		some platforms support devices that have their
>> -		own settings for cache use which can over-ride
>> -		these bits.
>> +		Bitmask of shareable resource with other executing entities
>> +		(e.g. I/O). Applies to all instances of this resource. User
>> +		can use this when setting up exclusive cache partitions.
>> +		Note that some platforms support devices that have their
>> +		own settings for cache use which can over-ride these bits.
>> +
>> +		When "io_alloc" is enabled, a portion of each cache instance can
>> +		be configured for shared use between hardware and software.
>> +		"bit_usage" should be used to see which portions of each cache
>> +		instance is configured for hardware use via "io_alloc" feature
>> +		because every cache instance can have its "io_alloc" bitmask
>> +		configured independently via io_alloc_cbm.
> 
> io_alloc_cbm -> "io_alloc_cbm" (to consistently place names of resctrl files in quotes)

Sure.

> 
>> +
>>   "bit_usage":
>>   		Annotated capacity bitmasks showing how all
>>   		instances of the resource are used. The legend is:
>> @@ -109,16 +116,16 @@ related to allocation:
>>   			"H":
>>   			      Corresponding region is used by hardware only
>>   			      but available for software use. If a resource
>> -			      has bits set in "shareable_bits" but not all
>> -			      of these bits appear in the resource groups'
>> -			      schematas then the bits appearing in
>> -			      "shareable_bits" but no resource group will
>> -			      be marked as "H".
>> +			      has bits set in "shareable_bits" or "io_alloc_cbm"
>> +			      but not all of these bits appear in the resource
>> +			      groups' schematas then the bits appearing in
> 
> I understand that you are just copying this but "schemata" is plural of "schema". Since you
> are copying this text, could you please fix "schematas" to be "schemata" while doing so?

Sure.

Thanks
Babu