From time to time, often after I’ve restored from sleep or finished playing a Steam game, one of my CPU cores is pinned at 100% with no indication of what might be doing it. Running htop, btop, or GNOME system monitor all show the same thing: CPU0 at 100% while the rest are doing near-nothing, and no process in particular seems to be using those resources.
If I restart, it’s back to normal, and sometimes I can play a game in Steam or let the computer go to sleep and it doesn’t do this, but it happens often enough that’s annoying/confusing so I’d like to know if there’s a way to either (a) diagnose which processes are using which CPU cores, or (b) somehow “reset” the checking of these values to make sure that something’s not just being misreported.
This is a desktop system running Arch & GNOME.
Show kernel threads, it’s a setting in the htop config menu that is off by default.
There it is! Thank you! It’s a process owned by root called kworker/0:0+kacpid. Any idea what that is?
[Edit 1] Interestingly, I can’t even kill -9 it.
[Edit 2] With kworker kacpid to work with, I did a quick search and found this SO page that has some interesting information that I only partially understand, but the following worked like a charm:
# grep -Ev "^[ ]*0" /sys/firmware/acpi/interrupts/gpe?? | sort --field-separator=: --key=2 --numeric --reverse | head -1
/sys/firmware/acpi/interrupts/gpe09:11131050 STS enabled unmasked
# echo disable > /sys/firmware/acpi/interrupts/gpe09
It’s not clear to me what an interrupt is or whether this gpe09 value is meant to be persistent across reboots, or why this only seems to be happening in the last couple months, but if I can make it go away by running the above from time to time, I guess it’s alright?
An interrupt is an input that can be triggered to interrupt normal execution. It is used for e. g. hardware devices to signal the processor something has happened that requires timely processing, so that real-time behavior can be achieved (for variable definitions of real-time). Interrupts can also be triggered by software, and this explanation is a gross oversimplification, but that information is what is most likely relevant and interesting for your case at this point.
The commands you posted will sort the interrupts and output the one with the highest count (via head -1), thereby determining the interrupt that gets triggered the most. It will then disable that interrupt via the user-space interface to the ACPI interrupts.
One of the goals of ACPI is to provide a kind of general hardware abstraction without knowing the particular details about each and every hardware device. This is facilitated by offering (among other things), general purpose events - GPEs. One of these GPEs is being triggered a lot, and the processing of that interrupt is what causes your CPU spikes.
The changes you made will not persist after a reboot.
Since this is handled by kworker, you could try and investigate further via the workqueue tools: https://github.com/torvalds/linux/tree/master/tools/workqueue
In general, Linux will detect if excessive GPEs are generated (look for the term “GPE storm” in your kernel log) and stop handling the interrupts by switching to polling. If that happens, or if the interrupts are manually disabled, the system might not react to certain events in a timely manner. What that means for each particular case depends on what the interrupts are being responsible for - hard to tell without additional details.
the system might not react to certain events in a timely manner.
But still react? Resource for read more?
That’s a kernel worker for ACPI. It sounds like you may have a driver for something that is misbehaving.
To me it sounds like your root cause is either a driver problem or your hardware is misbehaving a little bit in a way the driver doesn’t expect, firing a lot of interrupts that shouldn’t normally happen.
If this seems to resolve your issue, I wouldn’t lose any sleep over it. I would think my hardware is a little bit weird or there’s a bug somewhere in the driver for it. You can also try different kernel versions if your distribution gives you the option, because kernels come with different versions of drivers.
I blame Daniel
It’s the Linux version of steam taking advantage of idle time to process shaders. It’s a critical part of making all those proton launched games working right. I wish it had better control for when to run it but it is what it is.
Just as a PSA, the feature is currently somewhat bugged and really should be avoided. For anything that’s not a low-end PC, your machine can handle the compilation during runtime easily and do it much faster.
For low-ends, it compiles so many unnecessary shaders (such as all workshop content that you might not even have), it often takes 10x longer to compile everything (which you have to recompile on every driver or game cache update) than just playing the game and watching a replay first or something.
“Critical” as in not really needed.
It is very bugged and constantly runs even if it isn’t doing anything. It will also max out your disk IO for hours at a time with an HDD for larger game storage.
I have had it off for 1.5 years across 3 OS installs and have never had a problem with stuttering or shader related problems in that time. It is really not needed anymore for 95% of games since the Linux async solutions were merged.
Maybe if one uses severely out of date kernels it is critical
I have been fighting with this for a long time, do you have an external monitor? I find this happens if I wake from light-sleep (not hibernation) while an external monitor is plugged in.
One of my ACPI interrupts just goes off the charts.
In one of the other comments, we worked out that it was definitely something to do with ACPI, but yes I do have an external monitor. This is a desktop system.
Disabling the interrupt did the job, but I don’t know why it’s happening. If this is related to the monitor, could this be an Nvidia thing?
Similar thing happens to me with my two monitor setup. No problem when I use single monitor. No problem when I use two monitor. However when I plugged out the second monitor or switch to single monitor with my script, the CPU starts doing random spikes on single cores in short intervals. Only a reboot fixes this.
It’s probably Shader compilation. Funny enough the top result of my websearch is my own post/thread in Reddit 4 years ago. I had this exact same question on my old computer: https://www.reddit.com/r/linux_gaming/comments/kyf1wf/why_is_steam_using_one_core_always_but_doing/ Shader compilation is done from time to time in the background while Steam runs. This prepares games to run better.
Look if there is a process called fosselize. That was the process name back then doing the Shader compilation.
I’d never even heard of shader compilation. Apparently for the Steam Deck, Valve provides pre-compiled shaders for some games. What Is Shader Compilation and Why Does It Make PC Games Stutter?
Yes. That’s the benefit of having a single hardware to target. Same goes for consoles. They obviously know the hardware (like in Steam Deck’s case) and can precompile and ship it. There was plans (or just talks? not sure if this was ever realized) that users can download precompiled Shaders from other users, if its the exact same hardware.
Steam can download precompiled binaries that’s suitable for any system it they exist. If you turn it on, they’ll also collect shaders from you for others to download (not P2P).
It’s often said in r/linux_gaming that you no longer need shader precompilation, though without giving any reason. In my experience turning it off doesn’t have any performance penalty. But games with baked -in shader compilation will take 10 minutes to do it themselves on every launch which is annoying af.
