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XPS13 (9343), intel_pstate: stuck to minimum cpu-frequency
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., 4.2.0
2) How did I check the scaling_driver?
cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
intel_pstate
3) 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
15 Posts
0
October 7th, 2015 17:00
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
7 Posts
0
October 8th, 2015 00:00
Thank you for the hint,
however setting ignore_ppc does not make a difference.
Doug Smythies
5 Posts
1
October 9th, 2015 09:00
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
7 Posts
0
November 3rd, 2015 09:00
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!