linux-kernel - Re: [RFC PATCH 00/19] x86,fs/resctrl: Support for Global Bandwidth Enforcement and Priviledge Level Zero Association

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Message-ID: <d2ccabb1-e1de-4767-a7b0-9d72982e52af@intel.com>
Date: Mon, 9 Feb 2026 16:27:47 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: "Luck, Tony" <tony.luck@...el.com>, Babu Moger <babu.moger@....com>, "Drew
 Fustini" <fustini@...nel.org>, James Morse <james.morse@....com>, Dave Martin
	<Dave.Martin@....com>, Ben Horgan <ben.horgan@....com>
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Subject: Re: [RFC PATCH 00/19] x86,fs/resctrl: Support for Global Bandwidth
 Enforcement and Priviledge Level Zero Association

Adding Ben

On 2/3/26 11:58 AM, Luck, Tony wrote:
> On Wed, Jan 21, 2026 at 03:12:38PM -0600, Babu Moger wrote:
>> Privilege Level Zero Association (PLZA) 
>>
>> Privilege Level Zero Association (PLZA) allows the hardware to
>> automatically associate execution in Privilege Level Zero (CPL=0) with a
>> specific COS (Class of Service) and/or RMID (Resource Monitoring
>> Identifier). The QoS feature set already has a mechanism to associate
>> execution on each logical processor with an RMID or COS. PLZA allows the
>> system to override this per-thread association for a thread that is
>> executing with CPL=0. 
> 
> Adding Drew, and prodding Dave & James, for this discussion.
> 
> At LPC it was stated that both ARM and RISC-V already have support
> to run kernel code with different quality of service parameters from
> user code.
> 
> I'm thinking that Babu's implementation for resctrl may be over
> engineered. Specifically the part that allows users to put some
> tasks into the PLZA group, while leaving others in a mode where
> kernel code runs with same QoS parameters as user code.
> 
> That comes at a cost of complexity, and performance in the context
> switch code.
> 
> But maybe I'm missing some practical case where users want that
> behaviour.
> 
> -Tony