Re: CpuFreq Laptop Scaling broken?

[Viresh Kumar <viresh.kumar@linaro.org>]

On 25 August 2014 17:58, Harry van Haaren <harryhaaren@gmail.com> wrote:
> I'm attempting to squeeze the lowest audio-latency out of a laptop as possible,
> and in doing so would like to set the CPU to performance.
>
> CPU in laptop: Intel(R) Core(TM)2 Duo CPU T7300 @ 2.00GHz
>
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors
> ondemand performance
>
> $ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
> acpi-cpufreq
>
> # Attempt to set performance governer
> $ echo "performance" >/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
> bash: echo: write error: Invalid argument
>
> # Attempt to set min freq of 2GHz (max) of this core2duo
> $ echo 2000000 > /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq
> bash: /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq: Permission denied

You tried both these as root? Even 'sudo' may not work..

I haven't seen the rt code since sometime, what tag should I look at ?

I don't think there should be any such issues there..

> As far as I can tell, it is currently impossible on the -rt kernel to
> change CPU governer?
> This is necessary for reliable low-latency audio for laptop musicians.
>
> What is necessary to fix cpufreq on -rt? Cheers, -Harry
>
> PS: I've CC'd maintainers of cpufreq, I hope that's OK, otherwise
> please inform me of
> normal practices on linux-rt-users ML

That's fine I suppose.