Re: [PATCH] intel_idle: Fix C6S and C10 latency values for Pantherlake

[Artem Bityutskiy <dedekind1@gmail.com>]

On Tue, 2026-08-11 at 10:36 +0000, Kumar, Kaushlendra wrote:
> On Tue, 2026-08-11 at 13:47 +0530, <reviewer> wrote:
> > The current values are based on what I measured using wult/pbe tool.
> > 
> > I think it will be better to explain the problem and how this patch
> > fixes it, give some details about workload. And ideally, also provided
> > turbostat output when it runs in parallel with the workload before and
> > after this patch.
> 
> Thank you for the feedback.
> 
> Looking at other platforms in intel_idle, C-state latency values are
> generally sourced from BIOS ACPI _CST characterization data. For
> example, MTL-L C6 (exit_latency=140, target_residency=420) and ADL-L
> C6 (exit_latency=170, target_residency=500) match their respective
> ACPI _CST tables.

So there are platforms that have intel_idle table and that do not have
it.

> For PTL, I observed a discrepancy. The ACPI _CST on a Pantherlake-L
> device  reports:
> 
>   C6S: latency=127us, residency=381us
>   C10: latency=1048us, residency=3144us

Discrepancy -> difference.

> Could you clarify which reference was used for other platforms — ACPI
> _CST or wult — so we can apply a consistent methodology for PTL?

Platforms that do not have intel_idle custom table, use latency from
ACPI _CST table. It only provides latency. Target residency is
calculated as 3x latency.

I do not know about _CST numbers. I only know that in many cases they
are not what I can observe using wult tool.

Panther Lake is the only client platform that I measured with the tools
I developed, and submitted the numbers based on wult and pbe data that
I got.

Artem.