Specifying nohz_full breaks CPU frequency reporting
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
linux-signed-lowlatency-hwe-6.5 (Ubuntu) |
Confirmed
|
Undecided
|
Unassigned |
Bug Description
With the lowlatency kernel, if I specify "nohz_full=1-15" boot parameter then CPU frequency reporting doesn't work for the logical cores 1-15. That is, only logical core 0 shows varying CPU frequency in its /sys/devices/
Steps to reproduce:
1. Add "nohz_full=1-15" (specify the core numbers to include all logical cores except 0) to kernel boot options in /etc/default/grub.
2. Run `sudo update-grub` and reboot.
3. Upon booting, run a multithreaded workload. For example, run `openssl speed -multi $(nproc --all)`.
4. In another console, monitor CPU frequencies by running `watch cat /sys/devices/
Actual results:
All cores specified in "nohz_full" parameter always report their lowest frequency.
Despite that, the actual performance seems to be as if frequency scaling actually works (i.e. according to benchmarks, the performance seems to be similar with and without the "nohz_full" parameter).
Expected results:
All cores must report their actual frequency depending on the load.
ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: linux-image-
ProcVersionSign
Uname: Linux 6.5.0-15-lowlatency x86_64
NonfreeKernelMo
ApportVersion: 2.20.11-0ubuntu82.5
Architecture: amd64
CasperMD5CheckR
CurrentDesktop: KDE
Date: Tue Jan 30 23:39:51 2024
InstallationDate: Installed on 2015-05-01 (3196 days ago)
InstallationMedia: Kubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
SourcePackage: linux-signed-
UpgradeStatus: Upgraded to jammy on 2022-05-14 (626 days ago)
Status changed to 'Confirmed' because the bug affects multiple users.