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

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

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@amd.com>
>> ---
>> 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