Re: [PATCH v8 10/10] fs/resctrl: Update bit_usage to reflect io_alloc

[Reinette Chatre]

Hi Babu,

On 8/26/25 3:51 PM, Moger, Babu wrote:
> Hi Reinette,
> 
> On 8/7/2025 8:54 PM, Reinette Chatre wrote:
>> Hi Babu
>>
>> On 8/5/25 4:30 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.
>>>
>>> Update the bit_usage representation to reflect the io_alloc configuration.
>> ... but no update to the bit_usage docs :(
> 
> 
> Yes. Missed that.  Will update the text.
> 
> 
>>
>>> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
>>> ---
>> ..
>>
>>> ---
>>>   Documentation/filesystems/resctrl.rst | 19 +++++++++++++------
>>>   fs/resctrl/ctrlmondata.c              |  2 +-
>>>   fs/resctrl/internal.h                 |  2 ++
>>>   fs/resctrl/rdtgroup.c                 | 18 ++++++++++++++++--
>>>   4 files changed, 32 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
>>> index d955e8525af0..1e46231b929c 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.
>>> +
>>>   "bit_usage":
>> More ignored feedback. I was expecting changes to the "bit_usage" section.
>> https://lore.kernel.org/lkml/94d075e0-6703-449f-9c0c-8e5973349dff@xxxxxxxxx/
> 
> Yea.  Added following text now.
> 
> 
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index 273c9c9389a4..0a56829407c9 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -124,8 +124,11 @@ related to allocation:
>                         "X":
>                               Corresponding region is available for sharing and
>                               used by hardware and software. These are the
> -                             bits that appear in "shareable_bits" as
> -                             well as a resource group's allocation.
> +                             bits that appear in "shareable_bits" as well as a
> +                             resource group's allocation. When io_alloc is enabled,
> +                             the capacity bitmasks configured via io_alloc_cbm will
> +                             also appear here, indicating the cache regions shared
> +                             with I/O devices.

This sounds as though when a bit is set in io_alloc_cbm then its corresponding position
will contain an "X". An "X" will only be displayed if io_alloc_cbm has the corresponding
bit set *and* the bit appears in a resource group's allocation.

I think that patch #7 adds a very good definition of io_alloc_cbm and that it is
unnecessary to duplicate it. Simply referring to io_alloc_cbm should thus be fine with
user's search for it in the doc leading to a good description.

Considering this, how about just:
                "X":
                      Corresponding region is available for sharing and
                      used by hardware and software. These are the
                      bits that appear in "shareable_bits" or "io_alloc_cbm" as
                      well as a resource group's allocation.


Please also update the "H" section.

Reinette