RPI4 clock speeds and serial port

Having now got an 8GB Pi4 to use for FreeBSD the machine seems to
be relatively slow at buildworld, taking some 18 hours for a clean
start buildworld. Sysctl -a | grep freq reports in part:

....
 
hw.cpufreq.turbo: 0
hw.cpufreq.sdram_freq: 400000000
hw.cpufreq.core_freq: 200000000
hw.cpufreq.arm_freq: 600000000
hw.clock.108MHz-clock.frequency: 0
hw.clock.27MHz-clock.frequency: 0
hw.clock.otg.frequency: 0
hw.clock.osc.frequency: 0
dev.iicbus.0.frequency: 100000
dev.cpufreq.0.freq_driver: bcm2835_cpufreq0
dev.cpufreq.0.%parent: cpu0
dev.cpufreq.0.%pnpinfo: 
dev.cpufreq.0.%location: 
dev.cpufreq.0.%driver: cpufreq
dev.cpufreq.0.%desc: 
dev.cpufreq.%parent: 
dev.bcm2835_cpufreq.0.freq_settings: 1500/-1 600/-1
dev.bcm2835_cpufreq.0.%parent: cpu0
dev.bcm2835_cpufreq.0.%pnpinfo: 
dev.bcm2835_cpufreq.0.%location: 
dev.bcm2835_cpufreq.0.%driver: bcm2835_cpufreq
dev.bcm2835_cpufreq.0.%desc: CPU Frequency Control
dev.bcm2835_cpufreq.%parent: 
dev.cpu.0.freq_levels: 1500/-1 600/-1
dev.cpu.0.freq: 600
dev.iichb.0.frequency: 100000

/boot/msdos/config.txt contains

root@nemesis:~ # more /boot/msdos/config.txt
[all]
arm_64bit=1
dtparam=audio=on,i2c_arm=on,spi=on
dtoverlay=mmc
dtoverlay=disable-bt
device_tree_address=0x4000
kernel=u-boot.bin

[pi4]
#hdmi_safe=1
armstub=armstub8-gic.bin

There is no /boot/msdos/cmdline.txt file.

Can one change the cpu speed without disturbing the serial console
by using something like 

arm_freq=1750

in config.txt, provided adequate cooling provisions are made?

I'd rather not complicate use of the serial console at this point.
 
Thanks for reading!

bob prohaska
 

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