Re: kernel performance: 3.16 vs. 4.9
Am 05.02.2017 um 09:03 schrieb Matthias Bodenbinder:
> Hi,
>
> I have upgraded my PC to newest chipset and CPU: Kaby Lake, Z270 with i7-7700K.
>
> Out of curiosity I did a kernel benchmark. Comparing darktable performance with kernel 3.16.0-4-amd64 and 4.9.0-1-amd64. I use the following command to run darktable:
> darktable-cli test.CR2 test.jpg --core -d perf -d opencl
>
> The results are surprising for me. Kernel 4.9 very much outperformance kernel 3.16. Here are the results with and without opencl (using a Geforce GTX750TI):
>
> kernel 3.16 kernel 4.9
> with opencl 16 s 9 s
> without opencl 120 s 23 s
>
> Without opencl, that is with pure CPU performance, the difference is a factor of 5!
>
> Why is that? What am I missing? I can hardly believe that kernel 4.9 is so much faster.
>
> Matthias
>
>
>
>
Hi,
the issue is solved. It is related to the CPU frequency driver acpi-cpufreq vs. intel_pstate and the governor powersave vs.
performance.
With kernel 4.9 the default CPU frequency driver for my hardware is intel_pstate. And I had the governor set to "powersave" in /etc/default/cpufrequtils. I do not see big performance differences between "powersave" and "performance" settings with intel_pstate.
But with kernel 3.16 the default CPU frequency driver is acpi-cpufreq. With my settings in /etc/default/cpufrequtils it running in "powersave" mode which is giving this dramatic performance collapse. With governor "ondemand" or "performance" kernel 3.16 is as fast as kernel 4.9.
Sorry for the confusion.
Matthias
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