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

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Message-ID: <CAJZ5v0ic91RriXEHJkEFn0EkPKykmdEANimbKjAtdR0SwCZ4OA@mail.gmail.com>
Date: Thu, 20 Nov 2025 12:02:18 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Doug Smythies <dsmythies@...us.net>
Cc: Christian Loehle <christian.loehle@....com>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	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 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.