RPi and powerd, was: Re: RPI4 clock speeds and serial port ( temperatures idle and -j4 buildworld buildkernel )

[bob prohaska]

On Sat, Mar 20, 2021 at 09:20:36PM -0700, Mark Millard wrote:
> 
> You are getting the vast majority of the time
> benefit from powerd use compared to my build
> context (based on the world build times). Avoiding
> building to allow compiling non-arm could cut
> your time noticeably, possibly around 30 minutes
> for world.
>

Half an hour I can wait 8-) More likely I'll botch the changes.
 
After trying powerd on the Pi4 with success it was applied
to Pi3 and Pi2. Powerd seemed to work well on the Pi3, but
the Pi2 v1.1 stalled consistently in the building libraries
phase. The stall was unresponsive to the debugger escape.
After power-cycling and disabling powerd, the Pi2 picked
up where it left off. Not sure if this is a property of 
powerd or an artifact of my setup on the Pi2, being
14.0-CURRENT FreeBSD 14.0-CURRENT #13 main-f5e930b369:
executing
make -j4 -DWITH_META_MODE  buildworld 

There was an effect from powerd on the Pi2, but only
600MHz > 900MHz. The Pi3 went from 600 to 1200, the
Pi4 600 to 1500. There was no obvious serial console
disruption on any of the three machines. 


At least on the Pi4 and Pi3 use of -DWITH_META_MODE seems
notably faster than before, much more like use of -DNO_CLEAN.
Quite a bit has changed since my earlier gripes about needless
recompiles so it's hard to fairly credit the improvement. 

> 
> > The RPi4 support for powerd (cpufreq) was added
> > on 2020-Jun-20 but my RPi4B activity started
> > well before then. That is why I did not go down
> > the powerd path in how I configured things. It
> > will be interesting to compare to your time.
> > 

I always thought of powerd as a complication inflicted to
conserve battery life. I had no idea it could be used for
performance enhancement. Thank you, Klaus!

bob prohaska