Re: KS/Plumbers: c-state governor BOF

[Rik van Riel <riel@redhat.com>]

On 08/24/2012 01:01 PM, Rik van Riel wrote:

> Since a good number of us will be in San Diego next week, at
> Kernel Summit / Plumbers / etc, I will organize a c-state
> governor BOF for those who are interested.

Here are the note from today's c-state governor BOF session:

- idle time estimator can be improved to return more
   conservative values
- have a trace point to verify how well idle time estimation works,
   returning expected idle time for the current algorithm, expected
   idle time for a test algorithm, and actually measured idle time
- we can objectively measure whether one idle time estimation
   algorithm is better than another
- example: last 8 idle times are 180 200 30 210 1000 150 10000 190
   - average idle time around 1500, but not typical
   - typical idle time just under 200
   - almost all idle time spent in one interval
- scheduler and cpufreq people also want idle time
   statistics, idea is to move the idle time statistics
   to the scheduler
- having idle time statistics in the scheduler allows
   the stats to be migrated when the scheduler migrates
   a task
- interface: expected idle time, demotion time
   - if we sleep much more than the expected idle time, put
     CPU into a deeper c-state
   - on x86 timed mwait could be used
   - generic timer code would be usable too
   - take into account both the idle statistics and power break-even