RE: [PATCH v1 0/5] cpuidle: teo: Rework the idle state selection logic

[Doug Smythies]

Hi Rafael,

Further to my reply of 2021.07.04  on this, I have
continued to work with and test this patch set.

On 2021.06.02 11:14 Rafael J. Wysocki wrote:

>This series of patches addresses some theoretical shortcoming in the
> TEO (Timer Events Oriented) cpuidle governor by reworking its idle
> state selection logic to some extent.
>
> Patches [1-2/5] are introductory cleanups and the substantial changes are
> made in patches [3-4/5] (please refer to the changelogs of these two
> patches for details).  The last patch only deals with documentation.
>
> Even though this work is mostly based on theoretical considerations, it
> shows a measurable reduction of the number of cases in which the shallowest
> idle state is selected while it would be more beneficial to select a deeper
> one or the deepest idle state is selected while it would be more beneficial to
> select a shallower one, which should be a noticeable improvement.

I am concentrating in the idle state 0 and 1 area.
When I disable idle state 0, the expectation is its
usage will fall to idle state 1. It doesn't.

Conditions:
CPU: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz
HWP: disabled
CPU frequency scaling driver: intel_pstate, active
CPU frequency scaling governor: performance.
Idle configuration: As a COMETLAKE processor, with 4 idle states.
Sample time for below: 1 minute.
Workflow: Cross core named pipe token passing, 12 threads.

Kernel 5.14-rc3: idle: teo governor

All idle states enabled: PASS
Processor: 97 watts
Idle state 0 entries: 811151
Idle state 1 entries: 140300776
Idle state 2 entries: 889
Idle state 3 entries: 8

Idle state 0 disabled: FAIL <<<<<
Processor: 96 watts
Idle state 0 entries: 0
Idle state 1 entries: 65599283
Idle state 2 entries: 364399
Idle state 3 entries: 65112651

Kernel 5.14-rc3: idle: menu governor

All idle states enabled: PASS
Processor: 102 watts
Idle state 0 entries: 169320747
Idle state 1 entries: 1860110
Idle state 2 entries: 14
Idle state 3 entries: 54

Idle state 0 disabled: PASS
Processor: 96.7 watts
Idle state 0 entries: 0
Idle state 1 entries: 141936790
Idle state 2 entries: 0
Idle state 3 entries: 6

Prior to this patch set:
Kernel 5.13: idle: teo governor

All idle states enabled: PASS
Processor: 97 watts
Idle state 0 entries: 446735
Idle state 1 entries: 140903027
Idle state 2 entries: 0
Idle state 3 entries: 0

Idle state 0 disabled: PASS
Processor: 96 watts
Idle state 0 entries: 0
Idle state 1 entries: 139308125
Idle state 2 entries: 0
Idle state 3 entries: 0

I haven't tried to isolate the issue in the code, yet.
Nor have I explored to determine if there might
be other potential idle state disabled issues.

... Doug