[PlanetCCRMA] problems with cpupower under ccrma kernels for Fedora

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Tue Aug 11 17:17:41 PDT 2015

On 08/11/2015 12:47 PM, Roman Hershkovich wrote:
> I have similar issue - my CPU always run underclocked and making latency
> while transferring to faster or slower mode.
> Is there a solution for this someone?

What distro version and what kernel? Which cpu do you have in your computer?

With current Intel cpus and current kernels (post 3.10.x, I think) the 
kernel support for power/clock management has changed. "Governors" are 
no longer used, although they seem to still be listed, instead a kernel 
module called intel_pstate is used. See if you have this:

ls -l /sys/devices/system/cpu/intel_pstate/

If so, you can control to a degree the performance with what is there, 
for example:

echo "100" > /sys/devices/system/cpu/intel_pstate/min_perf_pct

will force all cores to run at the fastest speed possible. If you look 
at the core speed you will actually see if fluctuate slightly anyway 
(although it will be near the top possible for your cpu).

I have found that for best low latency performance I have to set 
min_perf_pct to 100 and also disable hyperthreading either at the BIOS 
level or by stopping the hyperthreaded cores in the cpu (this is for 
when I run multithreaded apps that use a lot of cpu for sound 
processing, all orchestrated by jack of course).

Hope this helps...
-- Fernando

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