Re: [PATCH v1 0/2] cpuidle: teo: Refine handling of short idle intervals

[Rafael J. Wysocki]

On Wed, Apr 9, 2025 at 4:36 PM Doug Smythies <dsmythies@xxxxxxxxx> wrote:
>
> On 2025.04.03 12:16 Rafael J. Wysocki wrote:
>
> > Hi Everyone,
>
> Hi Rafael,
>
> > This series is intended to address an issue with overly aggressive selection
> > of idle state 0 (the polling state) in teo on x86 in some cases when timer
> > wakeups dominate the CPU wakeup pattern.
> >
> > In those cases, timer wakeups are not taken into account when they are
> > within the LATENCY_THRESHOLD_NS range and the idle state selection may
> > be based entirely on non-timer wakeups which may be rare.  This causes
> > the prediction accuracy to be low and too much energy may be used as
> > a result.
> >
> > The first patch is preparatory and it is not expected to make any
> > functional difference.
> >
> > The second patch causes teo to take timer wakeups into account if it
> > is about to skip the tick_nohz_get_sleep_length() invocation, so they
> > get a chance to influence the idle state selection.
> >
> > I have been using this series on my systems for several weeks and observed
> > a significant reduction of the polling state selection rate in multiple
> > workloads.
>
> I ran many tests on this patch set.
> In general, there is nothing significant to report.
>
> There seemed to be a little less power use for the adrestia test and it took a little longer to execute, but the average wakeup latency was the same.
>
> I am still having noise and repeatability issues with my main periodic tests, where CPU is swept from low to high at serveral work sleep frequencies.
> But I didn't observe anything significant.
>
> In order to use more shallow idle states with a periodic workflow, I launched 2000 threads with each at 113 Hertz work/sleep frequency and almost no work to do for each work packet.
> The patched version used between 1 and 1.5 less processor package power, at around 85 watts.
> The patched version spent about 3.5% in idle state 0 verses about 5% for the unpatched version.
> The patched version spent about 31.8% in idle state 1 verses about 30.2% for the unpatched version.
>
> Test computer:
> Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz
> Distro: Ubuntu 24.04.1, server, no desktop GUI.
> CPU frequency scaling driver: intel_pstate
> HWP: disabled.
> CPU frequency scaling governor: performance
> Ilde driver: intel_idle
> Idle governor: teo
> Idle states: 4: name : description:
>   state0/name:POLL                desc:CPUIDLE CORE POLL IDLE
>   state1/name:C1_ACPI          desc:ACPI FFH MWAIT 0x0
>   state2/name:C2_ACPI          desc:ACPI FFH MWAIT 0x30
>   state3/name:C3_ACPI          desc:ACPI FFH MWAIT 0x60
>
> ... Doug

Thank you!