Re: [RFC] mpam,x86,fs/resctrl: Generic schema description Proof of Concept

[Reinette Chatre]

Hi Chenyu,

On 6/10/26 8:26 PM, Chen, Yu C wrote:
> On 6/10/2026 11:59 PM, Reinette Chatre wrote:
> [ ... ]
> 
>>
>> -  This implies that all current and future ERDT capable systems will keep
>>     supporting MSR access with the legacy "percentage based control". Is this
>>     accurate? What will behavior be on an ERDT system that does not support
>>     MSR access with the percentage-based control?
> 
> Would it make sense to encourage users to switch to MMIO-based access if the
> platform replaces MSR interfaces with MMIO-based ones? One issue with emulating
> MSR-based access is that there may not be a strict 1:1 mapping between the MSR
> range and the MMIO range. Additionally, I am unsure whether both are strictly
> linearly scalable, so it could be challenging to create a proper mapping for
> msr_value_emulated = map(mmio_value) IIUC.

resctrl needs to continue to offer the MB percentage based control to not break any
existing tools that may take a while to transition to the new control interface.

I believe all architectures will encourage their users to use the finer grained
controls while I also expect users and their tools would gradually switch by themselves
to benefit from the improved capabilities.

Reinette