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

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Message-ID: <f3d6be2f-d08d-4731-951c-3439deabdd1c@arm.com>
Date: Sun, 25 Jan 2026 19:38:41 +0000
From: Christian Loehle <christian.loehle@....com>
To: Doug Smythies <dsmythies@...us.net>,
 "'Rafael J. Wysocki'" <rafael@...nel.org>
Cc: 'LKML' <linux-kernel@...r.kernel.org>,
 'Linux PM' <linux-pm@...r.kernel.org>
Subject: Re: [Update][PATCH v1.1 4/5] cpuidle: governors: teo: Adjust the
 classification of wakeup events

On 1/25/26 17:21, Doug Smythies wrote:
> On 2026.01.20 07:30 Rafael J. Wysocki wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>
>> 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@...el.com>
>> ---
>>
>> 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.

Thanks for the test!
So rjw-1-1 looks pretty much the same on rc5 as well, that's good.
I guess since the v1 of 4/5 change that did have an affect was added by Rafael
to mitigate the more liberal intercept counting, that should be fine then.
Interestingly here (in overall idle_misses) rjw (with 4/5 v1) has significantly
fewer idle_misses, while in state2 aboves it was much worse as per your previous
test results.

> 
> 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
>