Public bug reported:

I noticed that sometimes my Ubuntu 18.10 system feels sluggish. The
other times everything works fine. I don't know what triggers this weird
state. Suspend / resume? Maybe.

At first I thought this was maybe just a "perception issue", but then
when the sluggishness happened again, I fired up i7z and it looks that
CPU frequency almost never got over ~1600 MHz, But my CPU is perfectly
capable of going up to 4000 MHz!

I tried to fix it by setting 
echo 80 > /sys/devices/system/cpu/intel_pstate/min_perf_pct
echo 80 > /sys/devices/system/cpu/intel_pstate/max_perf_pct

I hoped I would force the CPU into almost max performance state this
way. And indeed, once I ran these commands, i7z showed steady 3100+ MHz
on all cores.

Then something weird happened - when I run some mild load on the CPU,
like just starting the IDE, during the startup the frequency ** dropped
back to about 800-1600 MHz ** and returned to 3100 MHz after the load
was gone (IDE loaded).

The CPU core temperatures shown by sensors / i7z are ok and typically at
about 40-50 C when this slowdown happens, so this doesn't look like
thermal throttling.

Any ideas?

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: linux-image-4.18.0-10-generic 4.18.0-10.11
ProcVersionSignature: Ubuntu 4.18.0-10.11-generic 4.18.12
Uname: Linux 4.18.0-10-generic x86_64
ApportVersion: 2.20.10-0ubuntu13
Architecture: amd64
AudioDevicesInUse:
 USER        PID ACCESS COMMAND
 /dev/snd/controlC0:  pkolaczk   3281 F.... pulseaudio
 /dev/snd/pcmC0D0c:   pkolaczk   3281 F...m pulseaudio
CurrentDesktop: ubuntu:GNOME
Date: Sun Oct 14 22:16:50 2018
DistributionChannelDescriptor:
 # This is a distribution channel descriptor
 # For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
 canonical-oem-somerville-xenial-amd64-20160624-2
HibernationDevice: RESUME=UUID=4836842e-0116-43c4-98b4-7a56427f81f1
InstallationDate: Installed on 2017-04-12 (549 days ago)
InstallationMedia: Ubuntu 16.04 "Xenial" - Build amd64 LIVE Binary 
20160624-10:47
MachineType: Dell Inc. Precision 5520
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=pl_PL.UTF-8
 SHELL=/bin/bash
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.18.0-10-generic 
root=UUID=7f76b1f0-8fef-41cc-86a2-99e554cb4d40 ro acpi_rev_override quiet 
splash iwlwifi.power_save=1 crashkernel=384M-:128M crashkernel=384M-:128M 
vt.handoff=1
RelatedPackageVersions:
 linux-restricted-modules-4.18.0-10-generic N/A
 linux-backports-modules-4.18.0-10-generic  N/A
 linux-firmware                             1.175
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/24/2018
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 1.11.0
dmi.board.name: 06X96V
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 10
dmi.chassis.vendor: Dell Inc.
dmi.modalias: 
dmi:bvnDellInc.:bvr1.11.0:bd07/24/2018:svnDellInc.:pnPrecision5520:pvr:rvnDellInc.:rn06X96V:rvrA00:cvnDellInc.:ct10:cvr:
dmi.product.family: Precision
dmi.product.name: Precision 5520
dmi.product.sku: 07BF
dmi.sys.vendor: Dell Inc.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: Incomplete


** Tags: amd64 apport-bug cosmic

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https://bugs.launchpad.net/bugs/1797802

Title:
  Erratic behavior of intel pstate CPU frequency control

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