[SOLVED] What's keeping my CPU from scaling down?

replica9000 · 03-02-2015, 12:09 PM

My install is about 5 years old, and has been through a few CPUs (previously i7-2600k and Phenom II X4 965 BE). I currently have an i7-4790K. I've noticed that the CPU rarely scales down below 4000MHz. It ranges from 4800MHz to 800MHz. It should scale down to about 800MHz when idle.

The running kernel:

Code:

# uname -a
Linux siduxion 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt4-3 (2015-02-03) x86_64 GNU/Linux

Both my system and LM17.1 have the same cpu related packages installed

Code:

# dpkg --get-selections | grep -i cpu
cpufrequtils                                    install
libcpufreq0                                     install

This is a screenshot from Linux Mint 17.1 LiveCD with i7z (0.27.2+git2013.10.12-g5023138-2).

This is from my install, same i7z.

Top doesn't show any significant CPU usage preventing the CPU from scaling.

smallpond · 03-02-2015, 12:29 PM

The default governor for CPUfreq is "performance" which will only slow your CPUs when they are on fire. Change to "ondemand" if you want low power when idle and max performance under load.

replica9000 · 03-02-2015, 12:54 PM

Quote:

Originally Posted by smallpond

The default governor for CPUfreq is "performance" which will only slow your CPUs when they are on fire. Change to "ondemand" if you want low power when idle and max performance under load.

Code:

# cpufreq-info
cpufrequtils 008: cpufreq-info (C) Dominik Brodowski 2004-2009
Report errors and bugs to cpufreq@vger.kernel.org, please.
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: 800 MHz - 4.80 GHz
  available cpufreq governors: performance, powersave
  current policy: frequency should be within 800 MHz and 4.80 GHz.
                  The governor "powersave" may decide which speed to use
                  within this range.
  current CPU frequency is 4.47 GHz (asserted by call to hardware).

I don't have the ondemand governor. Only performance and powersave. Even with powersave, it stays the same.

metaschima · 03-02-2015, 01:29 PM

Firefox is the most likely culprit.

replica9000 · 03-02-2015, 01:37 PM

Quote:

Originally Posted by metaschima

Firefox is the most likely culprit.

Nope. Stays the same, even without X running.

Also, I believe cpufreq has no control of the intel_pstate driver.

TobiSGD · 03-02-2015, 01:48 PM

Try to throw out cpufrequtils (it is deprecated anyways) and replace it with cpupower, see if that works.
Which governors are available depends on your kernel configuration, check if the ondemand governor is available there.

metaschima · 03-02-2015, 03:26 PM

Quote:

Originally Posted by replica9000

Nope. Stays the same, even without X running.

Also, I believe cpufreq has no control of the intel_pstate driver.

I recommend disabling the Intel Pstate driver and instead using:
CONFIG_X86_ACPI_CPUFREQ

I also recommend the ondemand governor for desktop systems.

replica9000 · 03-03-2015, 01:52 AM

I didn't realize Linux Mint was using the acpi-cpufreq driver by default. cpupower seems to be able to control that driver, whereas the intel_pstate driver seems to ignore any changes made by cpupower.

The downside to the acpi-cpufreq driver is that /proc/cpuinfo doesn't show the turbo frequencies.

gradinaruvasile · 03-07-2015, 07:00 AM

Try cpufreq-aperf.

Code:

sudo modprobe msr
sudo cpufreq-aperf

replica9000 · 03-07-2015, 03:29 PM

Quote:

Originally Posted by gradinaruvasile

Try cpufreq-aperf.

Code:

sudo modprobe msr
sudo cpufreq-aperf

Thanks for the info. I had written a script for get the current frequencies. Seems to work alright. I might play with the output of cpufreq-aperf too.

Code:

#!/bin/bash

# Get CPU's max non-turbo frequency
max_freq=$(rdmsr 0xce -f 15:8 -d | awk '{print $1*100,$2}')

socket0_aperf=0
socket0_mperf=0

while true; do

# Get aperf/mperf for all cores
socket0_aperf2=$(rdmsr -a 0xe8 -d 2> /dev/null)
socket0_mperf2=$(rdmsr -a 0xe7 -d 2> /dev/null)

# Calculate difference between aperf/mperf
socket0_aperf_diff=$(paste <(echo "$socket0_aperf2") <(echo "$socket0_aperf") | awk '{print $1-$2,$3}')
socket0_mperf_diff=$(paste <(echo "$socket0_mperf2") <(echo "$socket0_mperf") | awk '{print $1-$2,$3}')

socket0_aperf=$socket0_aperf2
socket0_mperf=$socket0_mperf2

CPUFREQ=$(paste <(echo "$socket0_aperf_diff") <(echo "$socket0_mperf_diff") | awk '{print ($1*'"$max_freq"')/$2,$3}' | awk -F "." '{print $1}' | sed 's/\s*$//g')

# The output
CORE00=$(echo "$CPUFREQ" | head -1); echo "Core 0: $CORE00 MHz"
CORE01=$(echo "$CPUFREQ" | head -2 | tail -1); echo "Core 1: $CORE01 MHz"
CORE02=$(echo "$CPUFREQ" | head -3 | tail -1); echo "Core 2: $CORE02 MHz"
CORE03=$(echo "$CPUFREQ" | head -4 | tail -1); echo "Core 3: $CORE03 MHz"
CORE04=$(echo "$CPUFREQ" | head -4 | tail -1); echo "Core 4: $CORE04 MHz"
CORE05=$(echo "$CPUFREQ" | head -4 | tail -1); echo "Core 5: $CORE05 MHz"
CORE06=$(echo "$CPUFREQ" | head -4 | tail -1); echo "Core 6: $CORE06 MHz"
CORE07=$(echo "$CPUFREQ" | head -4 | tail -1); echo "Core 7: $CORE07 MHz"
echo " "

sleep 1

done

exit