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

[Oleg Samarin]

I've made more testing

> > echo "100" > /sys/devices/system/cpu/intel_pstate/min_perf_pct increases
> > CPU does not speed up so much so it cann't be a workaround.
> 
> How much faster does it go with min_perf_pct set to 100?

Seems, it solves the issue:

3.4.17, min_perf_pct=100:
        Core [core-id]  :Actual Freq (Mult.)	  C0%   Halt(C1)%  C3 %   C6 %
        Core 1 [0]:	  4420.54 (44.21x)      26.8      56    8.22       1
        Core 2 [1]:	  4483.19 (44.83x)      49.9     8.1    25.2       1
        Core 3 [2]:	  4509.71 (45.10x)      9.28    21.2    65.5       1
        Core 4 [3]:	  4559.41 (45.59x)      57.7    1.32    19.1    2.19

> It would seem the thresholds for changing the frequency have changed. Or 
> the underlying algorithm. But setting min_perf_pct to 100 should bypass 
> that. What do you see in the other variables in 
> /sys/devices/system/cpu/intel_pstate?

There are only three variables:

(3.4.17)
max_perf_pct without=100
min_perf_pct=33
no_turbo=0

> 
> Did you try to run without the intel_pstate driver? 
> (intel_pstate=disable in the kernel boot line).

There is somee sound distortion:

3.4.17 intel_pstate=disable ondemand
       Core [core-id]  :Actual Freq (Mult.)	  C0%   Halt(C1)%  C3 %   C6 %
        Core 1 [0]:	  2404.26 (24.05x)	43.8    46.2    21.9       1
        Core 2 [1]:	  3508.47 (35.09x)      15.3    29.9    53.3       1
        Core 3 [2]:	  2814.05 (28.15x)	38.5    45.9    21.2       1
        Core 4 [3]:	  3180.39 (31.81x)      53.8    29.1    18.9    1.72

3.12.12 intel_pstate=disable ondemand
       Core [core-id]  :Actual Freq (Mult.)	  C0%   Halt(C1)%  C3 %   C6 %
        Core 1 [0]:	  2372.48 (23.72x)      62.6      45    10.3       1
        Core 2 [1]:	  2319.15 (23.19x)      45.8    42.3    16.6    9.89
        Core 3 [2]:	  1886.32 (18.86x)      15.3    89.5       1       1
        Core 4 [3]:	  1970.62 (19.71x)	42.7      34    31.9    9.36