ubuntu not work with tickless kernel boot option

[Kai Qiang Wu(Kennan)]

For redhat, we have such guide like
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/pdf/Performance_Tuning_Guide/Red_Hat_Enterprise_Linux-7-Performance_Tuning_Guide-en-US.pdf

and for tickless kernel, (use dynamic tickless ways)

1. config grub with following cmdline

$ cat /etc/default/grub
# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.
# For full documentation of the options in this file, see:
# info -f grub -n 'Simple configuration'

GRUB_DEFAULT=0
GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=10
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash isolcpus=1-2 nohz_full=1-2"
GRUB_CMDLINE_LINUX=""

I used nohz_full here, and it is CPU 1, 2 here.

2. update-grub after that.
3. Then reboot system

4. execute following
$ sudo perf stat -C 1 -e irq_vectors:local_timer_entry taskset -c 1 stress -t 1 -c 1
stress: info: [3869] dispatching hogs: 1 cpu, 0 io, 0 vm, 0 hdd
stress: info: [3869] successful run completed in 1s

 Performance counter stats for 'CPU(s) 1':

               252 irq_vectors:local_timer_entry

       1.001491203 seconds time elapsed

It always 252, (the default 250 HZ), seems tickless kernel option not have any effect, whether config it or not, both have same results.

[Brad Figg (brad-figg)]

This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:

apport-collect 1587265

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Kai Qiang Wu(Kennan) (wkqwu)]

I could not run it, as

test@test-ThinkCentre-M92P:~$ apport-collect 1587265
ERROR: connecting to Launchpad failed: [Errno 110] Connection timed out
You can reset the credentials by removing the file "/home/test/.cache/apport/launchpad.credentials"

and also I am not sure if that report could collect sensitive info from my system or not, so I could not upload such log now.

I think the description is clear, so mark it confirmed now,
Let me know if have other ways to collect logs. Thanks

[Joseph Salisbury (jsalisbury)]

Did this issue start happening after an update/upgrade? Was there a kernel version where you were not having this particular problem? This will help determine if the problem you are seeing is the result of a regression, and when this regression was introduced. If this is a regression, we can perform a kernel bisect to identify the commit that introduced the problem.

[Kai Qiang Wu(Kennan) (wkqwu)]

I used the default ubuntu desktop install (amd64 14.04) version

[Dan Streetman (ddstreet)]

What specific kernel version had the problem? You can check with:

uname -a

The CONFIG_NO_HZ_FULL kernel param was turned off at some point between trusty's 3.13 and xenial's 4.4, and without that kernel param enabled the nohz_full boot param has no effect.

[Itamar Turner-Trauring (itamarst)]

This is still the case in Ubuntu 20.04:

$ cat /boot/config-5.11.0-27-generic | grep HZ_FULL
# CONFIG_NO_HZ_FULL is not set

This is problematic insofar as HZ_FULL is apparently useful for reliable benchmarking (e.g. see https://vstinner.github.io/journey-to-stable-benchmark-system.html).

Would be nice to get this fixed!

[Dominic (ubuntu1178)]

Would be nice to at least get a tickless kernel option without having to compile my own every time it's updated, it's becoming a source of frustration.