Am 06.02.2017 um 00:12 schrieb Ben Caradoc-Davies: > On 06/02/17 09:59, Matthias Bodenbinder wrote: >> 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 > > Matthias that is very interesting. Your findings seem different to those > reported on Phoronix; no doubt the p-state driver is undergoing some changes > to improve Kaby Lake support: > http://www.phoronix.com/scan.php?page=article&item=pstate-cpufreq-kbl&num=1 > http://www.phoronix.com/scan.php?page=article&item=pstate-cpufreq-kbl&num=2 > https://www.phoronix.com/scan.php?page=news_item&px=P-State-Kabylake-Patching > > Kind regards, >
The phoronix article only compares the performance governors. It does not investigate the performance decrease with acpi-cpufreq+powersave. Based on the articles I made another test with kernel 4.9 + acpi-cpufreq + performance and compared it to kernel 4.9 + intel_pstate + performance. The difference after several runs is minimal 23-24 s for intel_pstate vs. 22 s for acpi-cpufreq. Not sure if that is meaningful but it seems to support what phoronix is reporting. Matthias
