Arch Linux

Description:

Since Kernel 5.12.0, kfence is enabled by default, but using it leads to a massive increase in Load Average (my "idle" servers moved from 0.1 to 0.55, even a minimal fresh install) and CPU consumption:

Kernel 5.11.16 / 2021-05-08

type max avg current
user 1.46 1.21 1.20
system 2.50 2.00 2.04
wait 0.182 0.00364 0
interrupt 1.07 0.796 0.800
softirq 0.980 0.623 0.598


Kernel 5.12.03 / 2021-05-13
type max avg current
user 1.69 1.23 1.14
system 4.31 2.87 2.93
wait 0.239 0.00419 0
interrupt 1.51 1.01 0.955
softirq 1.56 0.834 0.732

So, user seems to be the same, but system, wait, interrupt and softirq have increased roughly by 20 percent.

I've made another tests after this :
- If the kfence.sample_interval=0 option in kernel options, we're back to the 5.11.16 report.
- If the kfence.sample_interval=500 option in kernel options as in Android Kernel, we're nearly back to the 5.11.16 report : system, interrupt and softirq have increased roughly by 5 percent.

Tests are made on 3 different computers without the patch proposed by the kfence team some weeks ago, but not integrated into the upstream release.


Additional info:
* package core/linux 5.12.3-arch1-1
* proposed patch here :20210421105132.3965998-1-elver@google.com/"> https://lore.kernel.org/linux-mm/20210421105132.3965998-1-elver@google.com/
* openSUSE disabling kfence : https://bugzilla.opensuse.org/show_bug.cgi?id=1185565


Steps to reproduce:
Install 5.12.3 kernel upgrade from 5.11.16.