[fast/warm-reboot] add cpufreq.default_governor=performance to BOOT_OPTIONS

[stepanblyschak]

What I did

Set cpufreq.default_governor to performance for faster boot time. We observe consistent 1 sec improvement across several devices.

NOTE: This will apply to upgrades starting from 202405 since this is set in shutdown path to avoid any extra scripts running at boot time. Upgrade from older versions/branches will require a runtime patch to fast-reboot and warm-reboot script.

How I did it

Append this option to BOOT_OPTIONS variable.

How to verify it

Run fast-reboot or warm-reboot. Check:

admin@sonic:~$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
performance

After boot is finalized check that it is reset back to default:

admin@sonic:~$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
schedutil

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)

[nazariig]

@stepanblyschak let's add another check here:
/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
to make sure performance is really supported by CPU.
If not - log a relevant message and fallback to default

[stepanblyschak]

@nazariig governor is not a cpu feature, governor talks to the scaling driver (cpu specific) to set a target. scaling_available_governors - This list appears to be formed from the global cpufreq_governor_list in the cpufreq driver, where all governors that are included in the kernel are registered.

This cmdline param is fairly new (>5.9) but it is very appealing to use in this case (no need to wait for user space and sysfs to be available to set the governor from user space).

When this won't work - if the next kernel is not built with performance governor as a builtin driver it won't work (governor will not change).
For that, we would have to extract the kernel config from the next image rather then checking current image scaling_available_governors. And I generally don't think we would ever remove features from kernel in next releases.