Yo Achim! On Sun, 03 Jul 2016 23:20:10 +0200 Achim Gratz <strom...@nexgo.de> wrote:
> Gary E. Miller writes:
> >> No. That used to be "force_turbo=1", but is not needed anymore.
> >
> > As of what kernel? I notice RasPi's have all sorts of weird kernel
> > versions and patchsets.
>
> I've not kept notes, but the first Raspbian installation from about
> two years ago already didn't need it (until you wanted to void the
> warranty by overvolting also).
Thanks.
> > Worse my Odroid is at 3.10!
>
> Leave those out of the discussion, they aren't RasPi.
They run the same Gentoo as RasPi, just an older kernel. Not sure why.
> > Do I need to do this, or is 'performance' enough? What would you
> > put in config.txt to set the performance governor?
>
> If you haven't done any setup for lower and higher frequencies, the
> governor will never change frequencies (since there is only one to
> chose from).
When I had 'ondemand' set (the default), and nothing else set, my RasPi it
would toggle between a high and a low frequency. And that took some time to
settle.
> > How are you measuring? Eyeballing 'ntpq -p' or running a week of
> > gnuplots?
>
> Looking at the distribution of PPS arrival times and the resulting
> time offset in the loopstats.
You'll need some automated tools to see 5% changes.
> As long as there's no thunderstorm around it'll keep time
> within +-3ms range for the raw offsets taken every 16 seconds and
> +-300µs averaged over 3.5 minutes.
A GPS HAT will beat that by over 100x. If that matters to you.
Plug and play.
> Based on your time plots I'm probably not able to see that small an
> improvement. I was trying out the nohz=off in hope to get rid of PPS
> spikes that are alway 100ms or 200ms late,
I see something like that, just not as big a spike. Turned out to be
cron jobs. I'm now nice-ing my cron jobs.
> >> Keep in mind that the PPS
> >> timestamping is actually done by the VC4 and not the ARM in the BCM
> >> SoC.
> >
> > Very interesting. That is a new twist. Got a citation for that?
>
> The BCM SoC actually is a media processor with an ARM subsystem and
> not the other way around as typically found elsewhere. The timestamp
> counter and all I/O is provided by the VC4.
Got a citation for that?
RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
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