Re: [PATCH] cpuidle: menu: Fall back to polling if next timer event is near
From: Rafael J. Wysocki
Date: Mon Mar 21 2016 - 09:53:28 EST
On Saturday, March 19, 2016 11:54:39 PM Doug Smythies wrote:
> On 2016.03.19 17:34 Rafael J. Wysocki wrote:
> > Commit a9ceb78bc75c (cpuidle,menu: use interactivity_req to disable
> > polling) changed the behavior of the fallback state selection part
> > of menu_select() so it looks at interactivity_req instead of
> > data->next_timer_us when it makes its decision. That effectively
> > caused polling to be used more often as fallback idle which led to
> > significant increases of energy consumption in some cases.
> > Commit e132b9b3bc7f (cpuidle: menu: use high confidence factors
> > only when considering polling) changed that logic again to be more
> > predictable, but that didn't help with the increased energy
> > consumption problem.
> > For this reason, go back to making decisions on which state to fall
> > back to based on data->next_timer_us which is the time we know for
> > sure something will happen rather than a prediction (which may be
> > inaccurate and turns out to be so often enough to be problematic).
> > However, take the target residency of the first proper idle state
> > (C1) into account, so that state is not used as the fallback one
> > if its target residency is greater than data->next_timer_us.
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > ---
> > Doug, can you please see if this patch helps to address the problem
> > you're seeing?
> Yes, it appears to work great.
> > Commit e132b9b3bc7f is in linux-next only ATM, but it is a rebased
> > version of https://patchwork.kernel.org/patch/8602101/.
> So, I applied it to my existing kernel 4.5-rc7 work, i.e. the not
> rebased version.
> My reference = rvr7:
> Kernel 4.5-rc7 +
> Rafael's 3 patch set version 10 "cpufreq: Replace timers with utilization update callbacks" +
> Rik's patch (rvr5) "cpuidle: menu: use high confidence factors only when considering polling" +
> Rafael's patch from herein.
> My reference: k45rc7-rjw10-rvr7
> Aggregate Idle States in minutes for 2000 second test (some old data re-stated for reference):
> State k45rc7-rjw10 k45rc7-rjw10-reverted k45rc7-rjw10-rvr7
> 0.00 18.07 0.92 0.41
> 1.00 12.35 19.51 21.17
> 2.00 3.96 4.28 4.40
> 3.00 1.55 1.53 1.66
> 4.00 138.96 141.99 150.77
> total 174.90 168.24 178.41
> >>>> Kernel 4.5-rc7-rjw10: 61983 Joules
> >>>> Kernel 4.5-rc7-rjw10-reverted: 48409 Joules (test 2 was 55040 Joules)
> k45rc7-rjw10-rvr7: 54748 Joules
> The trace data has a record low number of long durations at 71.
I'm going to apply it for 4.6, then.