Intel CPU is forced to 400Mhz on all cores

[Gabor Kulcsar]

Recently my system became really sluggish - turned out that all 12of my CPU cores were running at about 400Mhz, despite the hardware limits reported by cpufreq-info:

hardware limits: 1.20 GHz - 3.20 GHz

Setting the governor to "performance" did not help. Then I noticed that there is an unkown driver marked as active besides the NVIDIA drivers:

"Using Processor microcode firmware for Intel CPUs from intel-microcode (proprietary)"

Disabling this driver and rebooting fixed the performance issues and CPU frequencies are now normal.

$ uname -a
Linux 3.19.0-25-generic #26-Ubuntu SMP Fri Jul 24 21:17:31 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

$ lsb_release -rd
Description: Ubuntu 15.04
Release: 15.04

$ apt-cache policy intel-microcode
intel-microcode:
  Installed: (none)
  Candidate: 3.20150121.1

$ cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 63
model name : Intel(R) Xeon(R) CPU E5-2620 v3 @ 2.40GHz
stepping : 2
microcode : 0x25
cpu MHz : 2912.343
cache size : 15360 KB
physical id : 0
siblings : 12
core id : 0
cpu cores : 6
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 15
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid xsaveopt
bugs :
bogomips : 4789.35
clflush size : 64
cache_alignment : 64
address sizes : 46 bits physical, 48 bits virtual
power management:
(...)

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: intel-microcode (not installed)
ProcVersionSignature: Ubuntu 3.19.0-25.26-generic 3.19.8-ckt2
Uname: Linux 3.19.0-25-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.17.2-0ubuntu1.1
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Aug 6 14:21:13 2015
InstallationDate: Installed on 2015-07-14 (22 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
SourcePackage: intel-microcode
UpgradeStatus: No upgrade log present (probably fresh install)