More observations: The problem does not happen if I disable Intel speed-step in BIOS. In this case, the CPU frequency of all cores goes to 2998 MHz whenever under load, and stays stable regardless of how long the load is applied.
The problem still happens even if intel_pstate=disable is passed to the kernel on boot. I tried forcing the CPU to its max frequency by using userspace governor and it worked only under idle load (freq ~3.9 GHz). As soon as multi-core load was applied, the CPU frequency dropped to ~1.6 GHz and went back to ~3.9 GHz only when the load was over. I observed a similar pattern when trying to force CPU only to 2.8 GHz - it still slowed down to 1.6 GHz under load, even though temperature should not be a problem in this case. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1797802 Title: Erratic behavior of intel pstate CPU frequency control Status in linux package in Ubuntu: Triaged Bug description: 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. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1797802/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
