RFC: powerd algorithms enhancements

[Aragon Gouveia]

| By Alexander Motin <mav at FreeBSD.org>
|                                          [ 2008-11-05 22:58 +0200 ]
> 1. To make it more SMP polite. Previous version uses average CPU load 
> that leads to the often load underestimation. It make powerd with 
> default configuration unusable on systems with more then 2 CPUs. I 
> propose to use summary load instead of average one. IMO this is the best 
> we can do without specially tuned scheduler. Also as soon as measuring 
> total load on SMP systems is more useful then total idle, I have 
> switched to it.
> 
> 2. To make powerd's operation independent from number and size of 
> frequency levels I have added internal frequency counter which 
> translated into real frequencies only on a last stage and only as good 
> as gone. Some systems may have only several power levels, while mine has 
> 17 of them, so adaptation time in completely different. It would be good 
> if algorithm was not depending on it.
> 
> 3. As part of previous I have changed adaptive mode to rise frequency on 
> demand up to 2 times and fall on 1/8 per time internal.
> 
> 4. For desktop (AC-powered) systems I have added one more mode - 
> "hiadaptive". It rises frequency twice faster, drops it 4 times slower, 
> prefers twice lower CPU load and has additional delay before leaving the 
> highest frequency after the period of maximum load. This mode was 
> specially made to improve interactivity of the systems where operation 
> capabilities are more significant then power consumption, but keeping 
> maximum frequency all the time is not needed.

I've thought of some of these too so will be trying your patch very soon and
report back.  Thanks for your work!


> 5. I have reduced polling interval from 1/2 to 1/4 of second. It is not 
> important for algorithm math now, but gives better system interactivity.

Something I've wondered about is the value of having a variable polling
interval.  My thinking is that on a workstation that stays powered 24/7 and
is unmanned for hours at a time, it might be useful for the polling
interval to drop significantly over time if load remains low.

Something else that'd be useful is an interface to allow operators to change
powerd's behaviour without restarting it with different paramters.


Regards,
Aragon