RPI4 clock speeds and serial port ( temperatures idle and -j4 buildworld buildkernel )

[tech-lists]

On Fri, Mar 19, 2021 at 11:29:51AM -0700, Mark Millard via freebsd-arm wrote:

>Back to temperature. See:
>
>https://www.raspberrypi.org/documentation/hardware/raspberrypi/frequency-management.md
>
>It indicates that 85C is the maximum temperature,
>though lower figures can be set. It also reports
>that a form of throttling starts at 80C by default.

I use -j6 [1] for buildworld/kernel steps on stable/13 and highest temp seen has 
been 72 degC at 25 ambient [2], when it's compiling clang and friends. Not measured
timings but it's less than a day. I'll have to try the .clang flags
you've posted elsewhere. What I do have, which cuts down compile time,
is a load of WITHOUT_SOMETHING= statements in /etc/src.conf covering stuff that'll
never be used in this particular context.

[1] still has enough horsepower to run eg mutt+vim and a nginx webserver comfortably. 
     I didn't choose -j6 out of anything more scientific than "well there's 4 cores so 
     let's make it j6 to keep it busy"
[2] implying maximum ambient is 33 for this case.

-- 
J.
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