[PlanetCCRMA] Performance degradation with kernel-rt-3.14.17-200.rt9.1.fc20.ccrma.x86_64

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Fri Sep 5 15:17:40 PDT 2014

On 09/05/2014 12:35 PM, Oleg Samarin wrote:
> Hello!


> I use Fedora 20 with PlanetCCRMA realtime kernel.
> After upgrading the kernel from kernel-rt-3.12.12-300.rt19.1.fc20.ccrma to
> the last one - kernel-rt-3.14.17-200.rt9.1.fc20.ccrma, the huge sound
> distortion started occurring. When I boot my station with kernel-rt-3.12.12,
> everything seems all right.

Did you try to confirm by, for example, looking at the output of top in 
both cases? Can you confirm that the cpus are stuck to low frequencies? 
What does /proc/cpuinfo report in your case?

> The most probably reason is a bug in intel_pstate driver, that prevents CPU
>   speeding up: https://bugzilla.kernel.org/show_bug.cgi?id=70941,  There is a
> patch that should solve this problem.

Is your system actually using the pstate_intel driver? If so, what 
happens if you try to get all cpus to run as fast as possible:

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

Does that make a difference?

> Could you include this patch in the next build of kernel-rt?

Sure, but it would be nice to get more feedback.
-- Fernando

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