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

Ralf Mardorf ralf.mardorf at alice-dsl.net
Tue Aug 28 08:53:07 CEST 2018


Hi,

some things seems to be distro specific and other depend on the used
CPU.

On Mon, 2018-08-27 at 15:58 -0700, Len Ovens wrote:
> 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 might use 'powersave' instead of 'ondemand' and the
default could be the one chosen by the kernel's config. I still don't
understand this relatively new GOV_SCHEDUTIL thingy, but I didn't have
done any research to learn something about it ;).

Regarding Ubuntu (at least for Xenial) there indeed is 'ondemand' in
/etc/rc.d/, /etc/init.d/. However, I stay with 'powersave' or 'ondemand'
as default and change the governor to 'performance' if I run an audio
session on all of my Linux installs. Batterie charge OTOH might suffer
from 'ondemand'. Thanks to this thread I might understand this
GOV_SCHEDUTIL thingy, INTEL_PSTATE seems to affect the defaults.

"Note: The intel_pstate driver supports only the performance and
powersave governors, but they both provide dynamic scaling. The
performance governor should give better power saving functionality than
the old ondemand governor
[ https://www.phoronix.com/scan.php?page=news_item&px=MTM3NDQ ]."
- https://wiki.archlinux.org/index.php/CPU_frequency_scaling#Scaling_governors

I noticed that 'irqbalance' is there, too. 

I don't have a link at hand, but IIRC it shouldn't be used with audio
real-time.

Just in case I run 'sudo apt purge irqbalance' right now, but usually
I'm using Arch where it never was installed.

Regards,
Ralf


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