RE: [Update][PATCH v1.1 4/5] cpuidle: governors: teo: Adjust the classification of wakeup events

[Doug Smythies]

On 2026.01.20 07:30 Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> If differences between target residency values of adjacent idle states
> of a given CPU are relatively large, the corresponding idle state bins
> used by the teo governors are large either and the rule by which hits
> are distinguished from intercepts is inaccurate.
>
> Namely, by that rule, a wakeup event is classified as a hit if the
> sleep length (the time till the closest timer other than the tick)
> and the measured idle duration, adjusted for the entered idle state
> exit latency, fall into the same idle state bin.  However, if that bin
> is large enough, the actual difference between the sleep length and
> the measured idle duration may be significant.  It may in fact be
> significantly greater than the analogous difference for an event where
> the sleep length and the measured idle duration fall into different
> bins.
>
> For this reason, amend the rule in question with a check that will
> only allow a wakeup event to be counted as a hit if the difference
> between the sleep length and the measured idle duration is less than
> LATENCY_THRESHOLD_NS (which means that the difference between the
> sleep length and the raw measured idle duration is below the sum of
> LATENCY_THRESHOLD_NS and 1/2 of the entered idle state exit latency).
> Otherwise, the event will be counted as an intercept.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
>
> v1 -> v1.1
>   * Drop the change in teo_select() along with the corresponding
>     part of the changelog (after receiving testing feedback from
>     Christian)

With this updated patch I have not observed any difference in testing
results or power consumption between kernels without or with the
5 patch set:

c66de7fc0157 (HEAD -> rjw-1-1) cpuidle: governors: teo: Adjust the classification of wakeup events
25f70be81668 Revert "cpuidle: governors: teo: Adjust the classification of wakeup events"
f0ae302c4635 cpuidle: governors: teo: Refine intercepts-based idle state lookup
f5ad355214de cpuidle: governors: teo: Adjust the classification of wakeup events
1c5b66c336ea cpuidle: governors: teo: Refine tick_intercepts vs total events check
36148eea2ec2 cpuidle: governors: teo: Avoid fake intercepts produced by tick
8b1ad7bc8a7f cpuidle: governors: teo: Avoid selecting states with zero-size bins
0f61b1860cc3 (tag: v6.19-rc5, origin/master, origin/HEAD, master) Linux 6.19-rc5

My test system:
Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz, 6 cores 12 CPUs.
HWP: Enabled.
state0/name:POLL
state1/name:C1_ACPI
state2/name:C2_ACPI
state3/name:C3_ACPI

@Christian: I noticed that you like "idle misses" in test results. I have added
percent "idle misses" to my test results. An example graph is attached.

Legend:
rc5 = kernel 6.19-rc5
rjw = kernel 6.19-rc5 + original 5 patch set
rjw-1-1 = kernel 6.19-rc5 + current 5 patch set

See also my previous email [1] about the original 5 patch set:

[1] https://lore.kernel.org/linux-pm/003201dc895f$8cfb2540$a6f16fc0$@telus.net/

... Doug

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