Re: RE: [PATCH 1/2] x86/resctrl: Add io_alloc_min_cbm_all interface for CBM reset

[Babu Moger]

Hi Tony,

On 11/10/25 11:50, Luck, Tony wrote:
> > Does the following option work for you?
> >
> > # echo "*=0" > /sys/fs/resctrl/info/L3/io_alloc_cbm
> >
> >
> > Here,|*| represents all domains.
> >
> >
> > This functionality was introduced when adding support for the*"mbm_event" assign mode* (see [1]).
> > [1]https://lore.kernel.org/lkml/b894ad853e6757d40da1469bf9fca4c64684df65.1757108044.git.babu.moger@xxxxxxx/ <https://lore.kernel.org/lkml/b894ad853e6757d40da1469bf9fca4c64684df65.1757108044.git.babu.moger@xxxxxxx/> <https://lore.kernel.org/lkml/b894ad853e6757d40da1469bf9fca4c64684df65.1757108044.git.babu.moger@xxxxxxx/>
> > Also, this needs to be done for all the settings like L3, MBA also SMBA.
> >
> > # echo "L3:*=f" > /sys/fs/resctrl/schemata
> >
> > # echo "MB:*=128" > /sys/fs/resctrl/schemata
> >
> > I’d like to hear from Reinette and Tony if this seems like an acceptable
> > approach.
> >
> > Thanks
> Babu,
>
> It does look like a logical extension of the mbm_event assignment syntax.
>
> But might be awkward to use if the system has asymmetric domains. We don't
> currently. But if we wanted to support L2 cache allocation on hybrid platforms
> with a mix of P-core and E-core, those have historically supported different
> bit masks because the L2 caches may allow 12 bits for one core type and
> 16 for another. On such a platform:
>
> # echo "L2:*=fff" > schemata
>
> would work,. But
>
> # echo "L2:*=ffff" > schemata
>
> would try to set unimplemented bits on some cores and would fail.


I would consider this a user error, as the user is expected to know the 
supported value for the domain.
This situation can occur even now — we simply report the error and exit.

Thanks

Babu