XPS13 (9343), intel_pstate: stuck to minimum cpu-frequency

Question

Hi, analyzing a performance issue (not knowing whether my expectations are too high but assuming performance is too low...) I had to realize that cpu-frequency seems to be stuck to it's minimum (500 MHz) all the time. 1) Environment:    Dell XPS13 (9343)    Intel i5-5200 CPU@2.20 GHz    BIOS A05    Intel Wireless 7265    intel_pstate    Ubuntu 15.04  / 14.04 LTS    Kernel: several versions,                most of the time 3.19.0-28                but also tested with 4.0.0., 4.2.02) How did I check the scaling_driver?     cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver    intel_pstate3) How did I check the cpu-frequency?    a) lscpu |grep MHz    b) sudo watch -n 0,3 cat /sys/devices/system/cpu/cpu{0..3}/cpufreq/cpuinfo_cur_freq    c) cpufreq-info    d) powertop (Tab to 'Frequency stats')    On XPS13 powertop displays only two frequencies in 'Frequency stats':    500 MHz, 600 MHz.    On a different notebook (booted with the same  USB-stick) 'Frequency stats'    shows a whole bunch of different frequencies, from min-frequency up to max-frequency    (min-/max-freq. as reported by lscpu).4) How did I try to influence the (stuck) cpu-frequency?    a) by creating workload    b) by increasing minimum cpu-frequency:       cat /sys/devices/system/cpu/intel_pstate/min_perf_pct       18       echo '30' | sudo tee /sys/devices/system/cpu/intel_pstate/min_perf_pct       On the other notebook, booted with the same USB-stick, this changes       the cpu-frequency immediately to a higher value.       You can see cpu-frequency scaling up/down; it looks like not undergoing the       frequency defined via min_perf_pct.       On my XPS13 the CPU-frequency is tumbling around 500MHz,       mostly 499,984 MHz never higher than 500,240 MHz.       Trying to change CPU-frequency as described fails - no reaction at all.       The frequency always remains at ~500MHz.5) I have tested with several kernels, same results/behavior      Exception: With kernel 4.2.0 powertop two counted times showed additional     frequencies to 500 and 600 MHz: 1.100MHz, 2,7 GHz.     I can not reproduce this , it  did not happen by creating workload like starting     a program, etc. During program starts (Firefox, Writer, VMware-player...) the     frequencies displayed are  only 500, 600 MHz.     The system was pretty idle, Firefox was running, displaying the firefox-standard     -startpage (google) when additional frequencies have been displayed for a moment.6) Strange or confusing:     (Only) when running the system with acpi-cpufreq driver CPU frequencies are not stuck.    Under load they go up to  ~2.2 GHz. However, the performance does not increase    as one would expect.    (Pl. see:en.community.dell.com/.../20824758    and below)Questions:a) Do I have a problem of understanding?b) Could the stuck-to-min-cpu-frequency be a hardware issue? How likely is this? Thanks for any hint / support!

TheNitai · Answer

Not sure if this helps, but I see that the Xps13 has CPU throttling set. In order to change it you can do:

echo 1 > /sys/module/processor/parameters/ignore_ppc

and edit /etc/default/grub with

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash processor.ignore_ppc=1"

update-grub

However, this has an impact on battery life.

n13260 · Answer

Thank you for the hint,however setting ignore_ppc does not make a difference.

Doug Smythies · Answer

for this:

> 6) Strange or confusing:
> (Only) when running the system with acpi-cpufreq driver CPU frequencies are not stuck.
> Under load they go up to ~2.2 GHz. However, the performance does not increase
> as one would expect.

Please know that the acpi-cpyfreq driver reports CPU frequencies that have been asked for (p-states, really) and not what the CPU frequency actually is. Whereas the intel_pstate driver reports what the CPU frequencies actually were during the times that the CPU was in the C0 state during the last sample interval. When using the acpi-cpufreq driver, suggest you use turbostat to get information on the actual CPU frequencies.

n13260 · Answer

turbostat made the issue quite obvious: CPU frequency was in fact stucked. Dell replaced the mainboard and now everything is performing very :-) well! Doug, thank you so much for this hint!

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