CPU always in Turbo Boost frequency

[mariumotea]

Hi,

I buy a new system to be used as home server with Proxmox and i saw that cpuinfo report cpu frequency to be 4.0Ghz even when load is 0, while the nominal speed is 2.8Ghz (core i5-8400). I try to play with bios settings with no luck. In the end i boot Ubuntu 18.04 desktop from USB stick and i saw the cpu stay at 800Mhz when there is no load, so the problem must be related only to OS. I play also with scaling_governor but with no luck (echo powersave > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor)

root@pve:~# cat /proc/cpuinfo | grep "MHz"
cpu MHz         : 3898.811
cpu MHz         : 3899.243
cpu MHz         : 3895.974
cpu MHz         : 3890.933
cpu MHz         : 3893.654
cpu MHz         : 3892.945
root@pve:~#
root@pve:~# uname -r
4.15.18-4-pve
root@pve:~# top
top - 20:19:03 up 11 min,  1 user,  load average: 0.09, 0.19, 0.15
Tasks: 266 total,   1 running, 169 sleeping,   0 stopped,   0 zombie
%Cpu0  :  2.1 us,  2.1 sy,  0.0 ni, 95.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu1  :  2.1 us,  4.2 sy,  0.0 ni, 93.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu2  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu3  :  0.0 us,  2.2 sy,  0.0 ni, 97.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu4  :  2.1 us,  2.1 sy,  0.0 ni, 95.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu5  :  2.1 us,  2.1 sy,  0.0 ni, 95.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st

I'm using GPU passthrough, but there is no change when all vm's are stopped.

 

[mariumotea]

I go forward with this problem and found to be an issue with intel_pstate driver. I undo all my changes to modules made by me for GPU passthrough, just to be sure my customization did not create this problem. Then i added on grub intel_pstate=disable and i saw my cpu was running with different frequency based on realtime load.

root@pve:~# cat /proc/cpuinfo | grep "MHz" 
cpu MHz         : 1800.127 
cpu MHz         : 1800.139 
cpu MHz         : 1800.545 
cpu MHz         : 1800.551 
cpu MHz         : 1800.142 
cpu MHz         : 1800.080 
root@pve:~#  
root@pve:~#  
root@pve:~#  
root@pve:~# cat /proc/cpuinfo | grep "MHz" 
cpu MHz         : 900.468 
cpu MHz         : 900.651 
cpu MHz         : 900.062 
cpu MHz         : 900.584 
cpu MHz         : 900.184 
cpu MHz         : 900.047 
root@pve:~#  
root@pve:~#  
root@pve:~# cat /proc/cpuinfo | grep "MHz" 
cpu MHz         : 1363.916 
cpu MHz         : 1639.019 
cpu MHz         : 1777.989 
cpu MHz         : 1794.991 
cpu MHz         : 1564.574 
cpu MHz         : 1571.208

 

[wolfgang]

Hi,

if you use pstate throttling you will get VM stability problems.

 

[mariumotea]

So far i did not had any issues with intel_pstate disabled. But is not a problem if the cpu is in that high frequency all the time? I made a quick test and in idle the cpu is with 3°C hotter on 4Ghz vs ~1.2Ghz.

Marius.