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

[Babu Moger]

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@xxxxxxx>
> > > ---
> > > 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