linux-kernel - Re: [PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

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Message-ID: <f46bb011-83b1-4037-bc6f-eb7e72800e38@arm.com>
Date: Thu, 20 Nov 2025 13:35:00 +0000
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
 Doug Smythies <dsmythies@...us.net>
Cc: Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
 Reka Norman <rekanorman@...omium.org>, Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

On 11/20/25 11:02, Rafael J. Wysocki wrote:
> On Wed, Nov 19, 2025 at 11:52 PM Doug Smythies <dsmythies@...us.net> wrote:
>>
>> On 2025.11.13 07:22 Christian Loehle wrote:
>>> On 11/12/25 16:21, Rafael J. Wysocki wrote:
>>>> Hi,
>>>>
>>>> This is a bunch of teo cpuidle governor improvements, some of which are related
>>>> to a bug report discussed recently:
>>>>
>>>> https://lore.kernel.org/linux-pm/CAEmPcwsNMNnNXuxgvHTQ93Mx-q3Oz9U57THQsU_qdcCx1m4w5g@mail.gmail.com/
>>>>
>>>> The first patch fixes a bug that may cause an overly deep idle state
>>>> to be selected when the scheduler tick has been already stopped.
>>>>
>>>> Patch [2/4] removes an unnecessary function argument.
>>>>
>>>> Patch [3/4] makes teo_update() to use s64 as the data type for its local
>>>> variables more consistently.
>>>>
>>>> The last patch reworks the governor's decay implementation to also decay
>>>> metric values lower than 8.
>>>>
>>>
>>> Tested-by: Christian Loehle <christian.loehle@....com>
>>>
>>> Test results below, although there really isn't anything interesting in there.
>>> teo-1 to teo-4 (patches 1 to 4 respectively are essentially indistinguishable from
>>> teo-m = mainline)
>>
>> I tested the 4 patch set also, and also found no differences in results above
>> repeatability noise levels.
>>
>> Additionally, I added another patch (patch 5 of 4):
>> "cpuidle: governors: teo: Rework the handling of tick wakeups" [1]
>> Similar findings.
>>
>> Additionally, I added another patch (patch 6 of 4):
>> "sched/idle: disable tick in idle=poll idle entry" [2]
>> And found only one significant improvement, for only one test,
>> but only for the TEO idle governor:
>>
>> Kernel 6.18-rc4:
>> For a 6 pair fast ping-pong test (meaning no work per token stop):
>> teo: 5.53 uSec per loop, reference test
>> 4 of 4 patches: 5.53 uSec per loop, 0%
>> 5 of 4 patches: 5.54 uSec per loop, 0.2% (noise)
>> 6 of 4 patches: 4.77 uSec per loop, 13% better
>> 6 of 4 patches (again): 4.81 uSec per loop, 13% better
>> menu: 5.29 uSec per loop, 4.4% better
>> menu + patch 6 of 4: 5.28 uSec per loop, 4.5% better
>>
>> Idle state 0 usage:
>> 18% with patch 6, teo
>> 11% with menu
>> ~1% with mainline and not patch 6, teo.
>>
>> Idle state 1 usage:
>> almost 0 with patch 6, teo
>> ~6% with menu
>> 27% with mainline and not patch 6, teo.
>>
>> Power: About 100 watts. Patch 6 and teo does increase power use by about a watt or 2.
>>
>> Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz, 6 cores 12 CPUs.
>>
>> For clarity my branch log:
>> 3993913d7f81 (HEAD -> rjw-teo) sched/idle: disable tick in idle=poll idle entry
>> d9b12b8d62bf cpuidle: governors: teo: Rework the handling of tick wakeups
>> e47178c87272 cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold
>> 7fe32e411c2b cpuidle: governors: teo: Use s64 consistently in teo_update()
>> 490e6118e45d cpuidle: governors: teo: Drop redundant function parameter
>> 8f627f86062e cpuidle: governors: teo: Drop incorrect target residency check
>> 6146a0f1dfae (tag: v6.18-rc4, origin/master, origin/HEAD, master) Linux 6.18-rc4
>>
>> [1] https://lore.kernel.org/linux-pm/6228387.lOV4Wx5bFT@rafael.j.wysocki/
>> [2] https://lore.kernel.org/linux-pm/aQiWfnnSzxsnwa2o@tpad/
> 
> Thanks for the feedback, much appreciated!
> 
> I will likely have some more teo updates in the next cycle.

You're welcome, looking forward to reviewing them too.
I haven't tried to see what this would ideally look like for the -stable branches.
Just backport everything until the most recent applicable Fixes:?