[LAU] Xruns :(

[Len Ovens]

On Sat, 22 Nov 2014, Will Godfrey wrote:

> Eventually I found the cause. Going from linux kernel 3.2 to 3.16 :(
> This, apparently, does very aggressive CPU frequency scaling. Drop back to 3.2
> and all is sweetness and light again.

Frequency scaling does seem to cause problems

> The question is whether there is a reasonably straightforward way to stop this
> behaviour. Doing the usual searches doesn't seem to turn up anything useful.
>
> Any help gratefully appreciated.
>
> I would add that I've double checked that the bios is set for 'performance'.

Performance in the bios is probably not the cpu governor. In fact if that 
turns "Boost" on, that is bad. I thought I knew the answer to this.... but 
looking at this computer (atom based) I am not seeing what I would expect.

First, there is a file in /etc/init.d/ called ondemand. It deals with a 
directory:

/sys/devices/system/cpu/cpu0/cpufreq/

(actually a set of directories the cpu0 will also be cpu1 2 3 or whatever 
depemding on the number of cores, plus double if hyperthreading is on)

Ondemand first checks scaling_available_governors and then sets 
scaling_governor to ondemand. If you have this directory you should be 
able to (as root) set this to performance instead. Or edit the file in 
/etc/init.d/ to force performance instead of ondemand.

I am running 3.13.0-39-lowlatency here and will check some other machines 
to see if this directory is missing there too.


--
Len Ovens
www.ovenwerks.net