Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Thu, 27 Jul 2023 22:12:56 +0200 | Subject | Re: [PATCH v1] cpuidle: teo: Update idle duration estimate when choosing shallower state |
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On Thu, Jul 27, 2023 at 10:05 PM Rafael J. Wysocki <rjw@rjwysocki.net> wrote: > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > The TEO governor takes CPU utilization into account by refining idle state > selection when the utilization is above a certain threshold. The idle state > selection is then refined by choosing an idle state shallower than the > previously selected one. > > However, when this is done, the idle duration estimate needs to be updated > so as to prevent the scheduler tick from being stopped while the candidate > idle state is shallow, which may lead to excessive energy usage if the CPU > is not interrupted quickly enough going forward. Moreover, in case the > scheduler tick has been stopped already and the new idle duration estimate > is too small, the replacement candidate state cannot be used. > > Modify the relevant code to take the above observations into account. > > Fixes: 9ce0f7c4bc64 ("cpuidle: teo: Introduce util-awareness") > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > --- > > @Peter: This doesn't attempt to fix the tick stopping problem, it just makes > the current behavior consistent. > > @Anna-Maria: This is likely to basically prevent the tick from being stopped > at all if the CPU utilization is above a certain threshold. I'm wondering if > your results will be affected by it and in what way. > > --- > drivers/cpuidle/governors/teo.c | 33 ++++++++++++++++++++++++++------- > 1 file changed, 26 insertions(+), 7 deletions(-) > > Index: linux-pm/drivers/cpuidle/governors/teo.c > =================================================================== > --- linux-pm.orig/drivers/cpuidle/governors/teo.c > +++ linux-pm/drivers/cpuidle/governors/teo.c > @@ -397,13 +397,22 @@ static int teo_select(struct cpuidle_dri > * the shallowest non-polling state and exit. > */ > if (drv->state_count < 3 && cpu_data->utilized) { > - for (i = 0; i < drv->state_count; ++i) { > - if (!dev->states_usage[i].disable && > - !(drv->states[i].flags & CPUIDLE_FLAG_POLLING)) { > - idx = i; > + /* > + * If state 0 is enabled and it is not a polling one, select it > + * right away and update the idle duration estimate accordingly, > + * unless the scheduler tick has been stopped. > + */ > + if (!idx && !(drv->states[0].flags & CPUIDLE_FLAG_POLLING)) { > + s64 span_ns = teo_middle_of_bin(0, drv); > + > + if (teo_time_ok(span_ns)) { > + duration_ns = span_ns; > goto end; > } > } > + /* Assume that state 1 is not a polling one and select it. */
Well, I should also check if it is not disabled. Will send a v2 tomorrow.
> + idx = 1; > + goto end; > } > > /* > @@ -539,10 +548,20 @@ static int teo_select(struct cpuidle_dri > > /* > * If the CPU is being utilized over the threshold, choose a shallower > - * non-polling state to improve latency > + * non-polling state to improve latency, unless the scheduler tick has > + * been stopped already and the shallower state's target residency is > + * not sufficiently large. > */ > - if (cpu_data->utilized) > - idx = teo_find_shallower_state(drv, dev, idx, duration_ns, true); > + if (cpu_data->utilized) { > + s64 span_ns; > + > + i = teo_find_shallower_state(drv, dev, idx, duration_ns, true); > + span_ns = teo_middle_of_bin(i, drv); > + if (teo_time_ok(span_ns)) { > + idx = i; > + duration_ns = span_ns; > + } > + } > > end: > /* > > >
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