Arch Linux

gnufied

Member

Registered: 2015-04-15

Posts: 13

[SOLVED] T450s and odd problems with CPU frequency scaling

Following is my system configuration:

~> uname -a
Linux hyperion 4.1.2-2-ARCH #1 SMP PREEMPT Wed Jul 15 08:30:32 UTC 2015 x86_64 GNU/Linux

~>  cat /proc/cpuinfo
processor       : 3
vendor_id       : GenuineIntel
cpu family      : 6
model           : 61
model name      : Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz
stepping        : 4
microcode       : 0x1d
cpu MHz         : 800.007
cache size      : 4096 KB
physical id     : 0
siblings        : 4
core id         : 1
cpu cores       : 2
apicid          : 3
initial apicid  : 3
fpu             : yes
fpu_exception   : yes
cpuid level     : 20
wp              : yes

First thing is, when I had virtualization (VT-d and VT-x) enabled in BIOS, my machine was almost always running on 3.xGHz speed even when idling on battery, with powersave intel pstate governor.

Then I went in BIOS and disabled both VT-d and VT-x and rebooted the machine and now the processor frequency will not go beyond 800Mhz when running on battery. This is rather odd and it feels to me that, Pstate is not working as it should. I am not using any other cpu frequency driver fwiw:

  ~>cpupower frequency-info
  analyzing CPU 0:
  driver: intel_pstate
  CPUs which run at the same hardware frequency: 0
  CPUs which need to have their frequency coordinated by software: 0
  maximum transition latency: 0.97 ms.
  hardware limits: 500 MHz - 3.20 GHz
  available cpufreq governors: performance, powersave
  current policy: frequency should be within 500 MHz and 512 MHz.
                  The governor "powersave" may decide which speed to use
                  within this range.
  current CPU frequency is 800 MHz (asserted by call to hardware).
  boost state support:
    Supported: yes
    Active: yes

Last edited by gnufied (2015-07-31 15:56:18)

gnufied

Member

Registered: 2015-04-15

Posts: 13

Re: [SOLVED] T450s and odd problems with CPU frequency scaling

Another oddity is:

~> cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq 
520200

Which is rather low! I was thinking if my BIOS is setting the low limit:

~> cat /sys/devices/system/cpu/cpu0/cpufreq/bios_limit 
2600000

Which appears to be fine. I am not entirely sure, why scaling_max_freq is rather low.

Last edited by gnufied (2015-07-23 02:49:15)

gnufied

Member

Registered: 2015-04-15

Posts: 13

Re: [SOLVED] T450s and odd problems with CPU frequency scaling

my problem I think is unrelated to P-State driver or acpu-cpufreq driver. Using either driver when on battery, the machine runs on low frequency (800Mhz for PState and 500Mhz for acpi-cpufreq).  This is very new machine and I am not sure if I have a failing battery or adapter (which seems to trigger the problem in other cases reported by users).

Also, I booted with Arch Installation CD again in battery mode and it seems to use frequencies between 800-2600MHz nicely, so I am not entirely sure if this is a hardware problem. Unfortunately I got rid of Windows when I installed Arch. But I guess I am going to try and do that next.

gnufied

Member

Registered: 2015-04-15

Posts: 13

Re: [SOLVED] T450s and odd problems with CPU frequency scaling

I installed Fedora 22 on this machine and frequency scaling seems to be proper now. As in, when running on battery the frequency isn't locked to 800MHz anymore and it scales depending on load (as it should).

I think, there is something off in latest kernel vis-a-vis frequency scaling.

gnufied

Member

Registered: 2015-04-15

Posts: 13

Re: [SOLVED] T450s and odd problems with CPU frequency scaling

So I ended up reinstalling Arch after briefly trying out Fedora and I don't see this problem anymore. I am not sure what was causing it.