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

[Oleg Samarin]

В Вс, 07/09/2014 в 16:12 -0700, Fernando Lopez-Lezcano пишет:
> On 09/07/2014 03:26 AM, Oleg Samarin wrote:
> >
> > I recompiled kernel-rt-3.14.17 with the latest intel_pstate
> > driver from
> > https://github.com/torvalds/linux/blob/16405f98bca8eb39a23b3ce03e241ca19e7af370/drivers/cpufreq/intel_pstate.c
> > The behaviour rest the same as with intel_pstate from kernel-rt-3.14.17.
> 
> That's not good news :-(
> Just out of curiosity, what processor do you have?

Intel i7-2600K 3.4 GHz. The maximum multipliers for turbo burst have
been set in BIOS to 48, 47, 46, 45 (4.8 GHz when 1 active core, 4.7 -
when two, 4.6 - when three and 4.5 when all cores are active)

> 
> > I made more testing.
> >
> > Under 3.14.17, when I just play GO, jack DSP load becomes 100%, but CPU core speed
> > leaves 1600-1800 mhz and the sound is terrible.
> >
> > Here is a i7z
> 
> (Ah, cool, I did not know about this program.)

https://code.google.com/p/i7z/

> 
> >output at that time:
> >
> >          Core [core-id]  :Actual Freq (Mult.)	  C0%   Halt(C1)%  C3 %   C6 %
> >          Core 1 [0]:	  2143.82 (21.44x)      31.1    44.8    33.5    2.09
> >          Core 2 [1]:	  1994.62 (19.95x)      47.9    60.4    10.5       1
> >          Core 3 [2]:	  2077.24 (20.77x)      34.7    33.2    44.7       1
> >          Core 4 [3]:	  2284.95 (22.85x)      45.4    29.5    34.3    5.74
> >
> >
> > If I run mprime torture
> > test (a tool that loads CPU hard) with 1 single thread, the CPU speed
> > becomes 4500-4800 mhz, jack dsp load decreases and I can play GO without
> > any sound problems. It could be a temporary workaround for me.
> >
> > Here is a i7z output with one mprime thread:
> >
> >          Core [core-id]  :Actual Freq (Mult.)	  C0%   Halt(C1)%  C3 %   C6 %
> >          Core 1 [0]:	  4284.18 (42.85x)        31    39.3    20.6       1
> >          Core 2 [1]:	  4305.80 (43.07x)      30.6      38    22.2       1
> >          Core 3 [2]:	  4102.73 (41.04x)      98.4       0       0       0
> >          Core 4 [3]:	  4131.24 (41.32x)      38.2    24.2    28.3       1
> >
> >
> > 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?

I will test it tonorrow.

> > Under 3.12.12 playing GO activates CPU speed up itself, so running
> > mprime is not necessary.
> 
> 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?
> 
> Did you try to run without the intel_pstate driver? 
> (intel_pstate=disable in the kernel boot line).

Yes, I tested it but the result was better under 3.12 than under 3.14.
I'll post the i7z output tomorrow.

> Here:
> http://ccrma.stanford.edu/planetccrma/mirror/fedora/linux/planetcore/20/SRPMS/repoview/kernel.html
> 
> By the way, this only happens in the rt patched kernels? What is the 
> behavior in the latest Fedora kernel?

Unfortunally, I can not even start jack with the standard kernel with my
parameters:

jackd -S -R -P40 -dalsa -dhw:NVidia_560,7 -r96000 -p64 -n5 -s -P

Altering them may seriously change the CPU load.