[LAU] System Configuration: kernel, CPU frequency, hardware timers

[Len Ovens]

On Mon, 27 Aug 2018, Kevin Cosgrove wrote:

> #   | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
> sudo touch /etc/rc.d/rc.local
> cp /etc/rc.d/rc.local rc.local_cpufreq
> cat << EOF >> rc.local_cpufreq
> #!/bin/sh

Some things have changed with cpufreq.
- in days of old there was /etc/rc.d/*ondemand that ran 60 seconds after
 	startup. This means no matter what you set for cpufreq it gets
 	down graded 60 sec later. disable ondemand if your os comes with
 	it.
- Now days there is kernel modules that need to be loaded and effective
 	before changing cpufreq stuff, otherwise it doesn't work... and
 	ondemand has been moved to systemd to ensure this. So it is best
 	if your os uses systemd to move you cpufreq setting script to
 	systemd to replace ondemand. BTW this ondemand also waits 60
 	seconds.
- newer intel cpus have a thing called "Boost" that can change your cpus
 	frequency up and down above what performance sets it to. There are
 	three choices here: Turn boost off in bios. Turn it off at run
 	time. Set performances minimum and max speed to compensate...
 	maybe higher than performance would. (yes I have more xruns at
 	low latencies with Boost on)

Setting performance is not about making sure your cpu runs as fast as 
possible. It is about making sure the cpu speed does not change, It seems 
at speed down changes I get xruns. However, I have set cpu governor to 
USER and set it hard to 800Mhz (lowest possible) and still very good xrun 
performance (like none in 8 hours running) while ondemand still gives 
xruns. So choose your speed and monitor cpu temperature and run it at the 
speed that gives you the highest temperature you are comfortable with.

IMO you should be monitoring temperature anyway to catch dust build up or 
fan failure.

--
Len Ovens
www.ovenwerks.net