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

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Message-ID: <CAJZ5v0i2hf_npzB+btX53VBDP+29Xy3sbuo5y36mOTZVe39O+Q@mail.gmail.com>
Date: Thu, 20 Nov 2025 14:38:08 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Christian Loehle <christian.loehle@....com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Doug Smythies <dsmythies@...us.net>, 
	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 Thu, Nov 20, 2025 at 2:35 PM Christian Loehle
<christian.loehle@....com> wrote:
>
> 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:?

I've added a list to this commit:

https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=14c66155c4609f1a1207d4e716c5e722b8bf920e