[systemd-devel] Disabling cpufreq/boost at boot time sometimes fails

[Thomas HUMMEL]

On 13/07/2022 00:35, Silvio Knizek wrote:
> Am Dienstag, dem 12.07.2022 um 18:55 +0200 schrieb Thomas HUMMEL:


> Hi,

Hello,

thanks for your answer

> 
> first of all, no need for /sys in /etc/fstab. /sys will _always_ be
> mounted by systemd.

Ok. This must be put by our image generating tool.

> Second, this sounds really depending on your used driver (acpi, amd, or
> intel). Check out the documentation at
> https://docs.kernel.org/admin-guide/pm/cpufreq.html

Well, this states:

"During the initialization of the kernel, the CPUFreq core creates a 
sysfs directory (kobject) called cpufreq under /sys/devices/system/cpu/."

This must explain why my modprobe.d (of acpi_cpufreq) seems to always 
work but not why tmpfiles.d or a .service unit :

As a matter of fact, I assume that since the /sys files seem to be 
created "at initialisation" or more precisely for the boost file, at 
driver, is exposed by the kernel module, this should be done long before 
systemd-tmpfiles-setup.service or my custom service are run ?

The only reason I can think of for those 2 latter setup to fail is that 
driver has not been loaded yet, hence the 
/sys/devices/system/cpu/cpufreq/boost file not existing yet, but I find 
this weird.


> Question I have is: why do you want to disable boosting?

One reason is because of rack density/input pdu power ratio.
Another might be performance consistency (at least for benching)

Thanks for your help

--
Thomas HUMMEL