RE: [RFT][PATCH v5 7/7] cpuidle: menu: Avoid selecting shallow states with stopped tick

[Doug Smythies]

On 2018.03.19 05:47 Thomas Ilsche wrote:
> On 2018-03-15 23:19, Rafael J. Wysocki wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>> 
>> If the scheduler tick has been stopped already and the governor
>> selects a shallow idle state, the CPU can spend a long time in that
>> state if the selection is based on an inaccurate prediction of idle
>> time.  That effect turns out to be noticeable, so it needs to be
>> mitigated.
>
> What are some common causes for that situation?
> How could I trigger this for testing?

It appeared quite readily with my simple 100% load
on one CPU test. Back then (V3) there only 6 patches in the set,
and before the re-spin there ended up being a patch 7 of 6, which
made a significant difference in both package power and the
histograms of times in each idle state.

Reference:
https://marc.info/?l=linux-pm&m=152075419526696&w=2

... Doug