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

["Moger, Babu" <babu.moger@amd.com>]

Hi Reinette,

On 8/28/2025 10:11 PM, Reinette Chatre wrote:
> 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@amd.com>
>>>> ---
>>> ..
>>>
>>>> ---
>>>>    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@intel.com/
>> 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.


Looks good.

>
>
> Please also update the "H" section.


Sure.

Thanks

Babu