Re: [PATCH v3 01/12] x86/resctrl: Support Privilege-Level Zero Association (PLZA)

[Moger, Babu]

Hi Reinette,

On 6/11/2026 6:23 PM, Reinette Chatre wrote:
> Hi Babu,
>
> On 4/30/26 4:24 PM, Babu Moger wrote:
> > Customers have identified an issue while using the QoS resource Control
>
> "Control" -> "control"?

ack

> > feature. If a memory bandwidth associated with a CLOSID is aggressively
>
> "a memory bandwidth" -> "memory bandwidth"?

ack.

> > throttled, and it moves into Kernel mode, the Kernel operations are also
>
> What does "it" refer to here? From text it seems to be the "CLOSID" but that
> does not sound right? Should "it" instead be something like "a task with that
> CLOSID"?

sure.

> "Kernel" -> "kernel"?

ack.
> > aggressively throttled. This can stall forward progress and eventually
> > degrade overall system performance. AMD hardware supports a feature
> > Privilege-Level Zero Association (PLZA) to change the association of the
> > thread as soon as it begins executing.
>
> "change the association of the thread as soon as it begins executing." I am
> not able to parse this.

How about ?

Customers have identified an issue while using the QoS resource Control
feature. If memory bandwidth associated with a CLOSID is aggressively
throttled, and a task with that CLOSID moves into kernel mode, the 
kernel operations are also aggressively throttled. This can stall 
forward progress and eventually degrade overall system performance.
AMD hardware supports a feature Privilege-Level Zero Association (PLZA)
to change the CPU association at the user-to-kernel transition, so the 
kernel execution can use a different association than user mode.

Privilege-Level Zero Association (PLZA) allows the user to specify a 
CLOSID and/or RMID associated with execution in Privilege-Level Zero. 
When enabled on a CPU, as the CPU enters Privilege-Level Zero, 
allocation and monitoring for that CPU will be associated with the PLZA 
CLOSID and/or RMID. Otherwise, the CPU will be associated with the 
CLOSID and RMID given by PQR_ASSOC.


> > Privilege-Level Zero Association (PLZA) allows the user to specify a CLOSID
> > and/or RMID associated with execution in Privilege-Level Zero. When enabled
> > on a HW thread, when the thread enters Privilege-Level Zero, transactions
>
> Could you please use consistent terminology throughout this series? This patch
> uses "HW thread"/"thread", the next patch then switches to "logical processor",
> and then by patch #4 the term seems to settle on "CPU". Could this just be
> "CPU" from here and throughout series to be consistent and easier to read?
>
> What is meant with "transactions"?  Is this just about memory transactions?
> Using this term combined with earlier "memory bandwidth" related problem description
> hints that this feature just impacts memory bandwidth allocation but from what
> I understand this impacts all allocation (CLOSID of all resources) and monitoring.
>
> Could "transactions" be replaced with "allocation and monitoring" and be
> more accurate?
>
> > associated with that thread will be associated with the PLZA CLOSID and/or
> > RMID. Otherwise, the HW thread will be associated with the CLOSID and RMID
> > identified by PQR_ASSOC.
> >
> > Add PLZA support to resctrl and introduce a kernel parameter that allows
> > enabling or disabling the feature at boot time.
> >
> > The GLBE feature details are documented in:
>
> "GLBE" -> "PLZA"?

ack.

> >    AMD64 Zen6 Platform Quality of Service (PQOS) Extensions:
> >    Publication # 69193 Revision: 1.00, Issue Date: March 2026
> >
> > available at https://bugzilla.kernel.org/show_bug.cgi?id=206537
>
> Please follow same style as what you used in the assignable counter enabling where
> this URL is provided via a "Link:" tag and then the text can refer to it. Specifically,
> 	Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 # [1]

Sure.

> > Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> > ---
> > v3: Code did not change. Patch order cahnged.
> >      Added documentation link.
> >
> > v2: Rebased on top of the latest tip.
> > ---
> >   Documentation/admin-guide/kernel-parameters.txt | 2 +-
> >   arch/x86/include/asm/cpufeatures.h              | 1 +
> >   arch/x86/kernel/cpu/resctrl/core.c              | 2 ++
> >   arch/x86/kernel/cpu/scattered.c                 | 1 +
>
> Please split changes to other subsystems and make these changes
> obvious with their own subject prefix to avoid sneaking changes into
> other subsystems via resctrl.

Ok. Will be two patches.
1. For Documentation/admin-guide/kernel-parameters.txt
2.  arch/x86/include/asm/cpufeatures.h
    arch/x86/kernel/cpu/resctrl/core.c
    arch/x86/kernel/cpu/scattered.c

thanks
Babu