Re: [PATCH v12 06/10] fs/resctrl: Add user interface to enable/disable io_alloc feature

[Babu Moger <bmoger@amd.com>]

Hi Reinette,

On 11/20/25 22:40, Reinette Chatre wrote:
> Hi Babu,
>
> On 11/20/25 10:35 AM, Babu Moger wrote:
>> Hi Reinette,
>>
>> On 11/12/25 18:57, Babu Moger wrote:
>>> AMD's SDCIAE forces all SDCI lines to be placed into the L3 cache portions
>>> identified by the highest-supported L3_MASK_n register, where n is the
>>> maximum supported CLOSID.
>>>
>>> To support AMD's SDCIAE, when io_alloc resctrl feature is enabled, reserve
>>> the highest CLOSID exclusively for I/O allocation traffic making it no
>>> longer available for general CPU cache allocation.
>>>
>>> Introduce user interface to enable/disable io_alloc feature and encourage
>>> users to enable io_alloc only when running workloads that can benefit from
>>> this functionality. On enable, initialize the io_alloc CLOSID with all
>>> usable CBMs across all the domains.
>>>
>>> Since CLOSIDs are managed by resctrl fs, it is least invasive to make
>>> "io_alloc is supported by maximum supported CLOSID" part of the initial
>>> resctrl fs support for io_alloc. Take care to minimally (only in error
>>> messages) expose this use of CLOSID for io_alloc to user space so that this
>>> is not required from other architectures that may support io_alloc
>>> differently in the future.
>>>
>>> When resctrl is mounted with "-o cdp" to enable code/data prioritization,
>>> there are two L3 resources that can support I/O allocation: L3CODE and
>>> L3DATA.  From resctrl fs perspective the two resources share a CLOSID and
>>> the architecture's available CLOSID are halved to support this.  The
>>> architecture's underlying CLOSID used by SDCIAE when CDP is enabled is the
>>> CLOSID associated with the CDP_CODE resource, but from resctrl's perspective
>>> there is only one CLOSID for both CDP_CODE and CDP_DATA. CDP_DATA is thus
>>> not usable for general (CPU) cache allocation nor I/O allocation. Keep the
>>> CDP_CODE and CDP_DATA I/O alloc status in sync to avoid any confusion to
>>> user space. That is, enabling io_alloc on CDP_CODE does so on CDP_DATA and
>>> vice-versa, and keep the I/O allocation CBMs of CDP_CODE and CDP_DATA in
>>> sync.
>>>
>>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>>> ---
>>> v12: Minor format fix in resctrl.rst.
>>>        Added text about writable files in the info section.
>>>        Removed Reviewed-by tag from Reinette as there are some new text changes from Dave.
>> Only this patch needs "Reviewed-by" tag.
>>
>> Gentle reminder with upcoming holidays.
> Thank you. I just added my "Reviewed-by" tag.


Thank you.

>
>> Hoping this series will be queued for next merge window.
>>
> I think it is getting late for new things.
>

Oh, okay. The series is ready now. It’s a pretty simple one, so I’ll let 
you decide

Thanks

Babu