Arch Linux

moep

Member

Registered: 2021-03-10

Posts: 3

Extreme lag when running niced CPU intensive process in background

I have a laptop which runs perfectly fine with Arch since years. However, recently in the last months an (unknown) update must have changed something.

My problem is as follows:
- When my laptop is connected to AC, I want to contribute to a distributed computing project (GIMPS, software is mprime which is also known for stress testing).
- mprime uses 100% CPU of course, but I have configured it to run with a nice level of 19.
- The problem is that as soon as mprime starts, my laptop gets laggy as hell now. For instance, starting an executable (something like "python -c 'print(1+1)'") or opening a new tab in Firefox will take a few seconds. Effectively, the laptop is unusable.
- It wasn't like this the years before, back then I didn't even notice when mprime was running in background (besides the laptop getting hot).
- I didn't change anything with mprime configuration at all.

How to debug this? I suspect some CPU scheduling algorithm has changed which prefers the already running processes before it starts new ones.

# cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
performance
performance
performance
performance

Last edited by moep (2021-03-10 20:18:42)

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 21,707

Re: Extreme lag when running niced CPU intensive process in background

What CPU exactly? The scheduling default changed from intel_pstate to cpufreq/schedutil in linux 5.8 for older CPU chipsets and this might lead to this result. You can currently still force it with the

intel_pstate=active

parameter.