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SubjectRe: [PATCH 2/3] cpuidle: teo: Avoid expecting unrealistic idle times
On Fri, Nov 15, 2019 at 2:24 AM Doug Smythies <dsmythies@telus.net> wrote:
>
> On 2019.11.14 15:51 Rafael J. Wysocki wrote:
> > On Wed, Nov 13, 2019 at 1:11 AM Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> >>
> >> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >>
> >> If an idle state shallower than the one "matching" the time till the
> >> next timer event is considered for selection, expect the idle duration
> >> to fall in the middle of the "bin" corresponding to that state rather
> >> than at the beginning of it which is unrealistic.
> >>
> >> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >> ---
> >> drivers/cpuidle/governors/teo.c | 9 ++++++++-
> >> 1 file changed, 8 insertions(+), 1 deletion(-)
> >>
> >> Index: linux-pm/drivers/cpuidle/governors/teo.c
> >> ===================================================================
> >> --- linux-pm.orig/drivers/cpuidle/governors/teo.c
> >> +++ linux-pm/drivers/cpuidle/governors/teo.c
> >> @@ -360,7 +360,14 @@ static int teo_select(struct cpuidle_dri
> >>
> >> if (max_early_idx >= 0) {
> >> idx = max_early_idx;
> >> - duration_ns = drv->states[idx].target_residency_ns;
> >> + /*
> >> + * Expect the idle duration to fall in the middle of the
> >> + * "bin" corresponding to idx (note that the maximum
> >> + * state index is guaranteed to be greater than idx at
> >> + * this point).
> >> + */
> >> + duration_ns = (drv->states[idx].target_residency_ns +
> >> + drv->states[idx+1].target_residency_ns) / 2;
> >> }
> >> }
> >
> > This change turns out to cause the governor to choose idle states that
> > are too deep or too shallow too often, so I'm withdrawing it.
>
> O.K. thanks for letting us know.
> I did see some differences in the testing I did so far, but hadn't drilled down
> into it yet.
> I am somewhat wondering about the above and below stats in general.
>
> By the way, I had a daft mistake in my post processing program, such that the
> "below" graph for idle state 0 was always plotting 0.
>
> Reference for that sweep test that I do (which is as far I got so far):
> http://www.smythies.com/~doug/linux/idle/teo-2019-11/sweep/index.html
>
> Legend:
>
> teo-v2: re-run of previous teo-v2 so that I could get non-zero idle state "below" data
> linux-next 2019.11.07 + cpuidle: Consolidate disabled state checks +
> [PATCH v2] cpuidle: Use nanoseconds as the unit of time
>
> teo-v3: teo-v2 + cpuidle: teo: Exclude cpuidle overhead from computations
>
> teo-v4: linux-pm + linux-next 2019.11.12 +
> cpuidle: teo: Avoid code duplication in conditionals
> cpuidle: teo: Avoid expecting unrealistic idle times
> cpuidle: teo: Avoid using "early hits" incorrectly
>
> teo-v5: teo-v4 + cpuidle: teo: Exclude cpuidle overhead from computations

Thanks for running the tests, appreciated!

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