Comment 0 for bug 1821441

This has been verified with a freshly reset bios. Every time I sleep Ubuntu and wake, the clock gets switched from TRC to HPET - and then processes such as gnome-shell take up an excessive amount of CPU (with trace showing clock_gettime being the culprit) - and general performance is severely degraded.

Here is the relevant part of syslog:
Mar 23 08:18:19 JTR4 kernel: [ 2921.476536] TSC synchronization [CPU#0 -> CPU#4]:
Mar 23 08:18:19 JTR4 kernel: [ 2921.476537] Measured 532 cycles TSC warp between CPUs, turning off TSC clock.
Mar 23 08:18:19 JTR4 kernel: [ 2921.476538] tsc: Marking TSC unstable due to check_tsc_sync_source failed
Mar 23 08:18:19 JTR4 kernel: [ 2921.476545] TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.
Mar 23 08:18:19 JTR4 kernel: [ 2921.476546] sched_clock: Marking unstable (2920879403495, 582702087)<-(2921692577659, -216036333)
Mar 23 08:18:19 JTR4 kernel: [ 2921.476773] cache: parent cpu4 should not be sleeping
Mar 23 08:18:19 JTR4 kernel: [ 2921.476839] microcode: CPU4: patch_level=0x0800820b
Mar 23 08:18:19 JTR4 kernel: [ 2921.477161] CPU4 is up
Mar 23 08:18:19 JTR4 kernel: [ 2921.477177] clocksource: Switched to clocksource hpet

This is in 18.04 LTS HWE, with an Asus Zenith Extreme Alpha motherboard and AMD Threadripper 2990WX CPU.

This looks like it is linked to this bug - as someone in the comments here shows a trace with clock_gettime using up excessive CPU, as well:
https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1773959

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-4.18.0-16-generic 4.18.0-16.17~18.04.1
ProcVersionSignature: Ubuntu 4.18.0-16.17~18.04.1-generic 4.18.20
Uname: Linux 4.18.0-16-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sat Mar 23 08:47:06 2019
InstallationDate: Installed on 2019-03-12 (11 days ago)
InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210)
SourcePackage: linux-signed-hwe
UpgradeStatus: No upgrade log present (probably fresh install)