One big difference that I’ve noticed between Windows and Linux is that Windows does a much better job ensuring that the system stays responsive even under heavy load.
For instance, I often need to compile Rust code. Anyone who writes Rust knows that the Rust compiler is very good at using all your cores and all the CPU time it can get its hands on (which is good, you want it to compile as fast as possible after all). But that means that for a time while my Rust code is compiling, I will be maxing out all my CPU cores at 100% usage.
When this happens on Windows, I’ve never really noticed. I can use my web browser or my code editor just fine while the code compiles, so I’ve never really thought about it.
However, on Linux when all my cores reach 100%, I start to notice it. It seems like every window I have open starts to lag and I get stuttering as the programs struggle to get a little bit of CPU that’s left. My web browser starts lagging with whole seconds of no response and my editor behaves the same. Even my KDE Plasma desktop environment starts lagging.
I suppose Windows must be doing something clever to somehow prioritize user-facing GUI applications even in the face of extreme CPU starvation, while Linux doesn’t seem to do a similar thing (or doesn’t do it as well).
Is this an inherent problem of Linux at the moment or can I do something to improve this? I’m on Kubuntu 24.04 if it matters. Also, I don’t believe it is a memory or I/O problem as my memory is sitting at around 60% usage when it happens with 0% swap usage, while my CPU sits at basically 100% on all cores. I’ve also tried disabling swap and it doesn’t seem to make a difference.
EDIT: Tried nice -n +19, still lags my other programs.
EDIT 2: Tried installing the Liquorix kernel, which is supposedly better for this kinda thing. I dunno if it’s placebo but stuff feels a bit snappier now? My mouse feels more responsive. Again, dunno if it’s placebo. But anyways, I tried compiling again and it still lags my other stuff.
The Linux kernel uses the CPU default scheduler, CFS, a mode that tries to be fair to all processes at the same time - both foreground and background - for high throughput. Abstractly think “they never know what you intend to do” so it’s sort of middle of the road as a default - every CPU cycle of every process gets a fair tick of work unless they’ve been intentionally
nice’d or whatnot. People who need realtime work (classic use is for audio engineers who need near-zero latency in their hardware inputs like a MIDI sequencer, but also embedded hardware uses realtime a lot) reconfigure their system(s) to that to that need; for desktop-priority users there are ways to alter the CFS scheduler to help maintain desktop responsiveness.Have a look to Github projects such as this one to learn how and what to tweak - not that you need to necessarily use this but it’s a good point to start understanding how the mojo works and what you can do even on your own with a few sysctl tweaks to get a better desktop experience while your rust code is compiling in the background. https://github.com/igo95862/cfs-zen-tweaks (in this project you’re looking at the set-cfs-zen-tweaks.sh file and what it’s tweaking in
/procso you can get hints on where you research goals should lead - most of these can be set with a sysctl)There’s a lot to learn about this so I hope this gets you started down the right path on searches for more information to get the exact solution/recipe which works for you.
I’d say
nicealone is a good place to start, without delving into the scheduler rabbit hole…I would agree, and would bring awareness of
ioniceinto the conversation for the readers - it can help control I/O priority to your block devices in the case of write-heavy workloads, possibly compiler artifacts etc.
“they never know what you intend to do”
I feel like if Linux wants to be a serious desktop OS contender, this needs to “just work” without having to look into all these custom solutions. If there is a desktop environment with windows and such, that obviously is intended to always stay responsive. Assuming no intentions makes more sense for a server environment.
Even for a server, the UI should always get priority, because when you gotta remote in, most likely shit’s already going wrong.
Totally agree, I’ve been in the situation where a remote host is 100%-ing and when I want to ssh into it to figure out why and possibly fix it, I can’t cause ssh is unresponsive! leaving only one way out of this, hard reboot and hope I didn’t lose data.
This is a fundamental issue in Linux, it needs a scheduler from this century.
You should look into IPMI console access, that’s usually the real ‘only way out of this’
SSH has a lot of complexity but it’s still the happy path with a lot of dependencies that can get in your way- is it waiting to do a reverse dns lookup on your IP? Trying to read files like your auth key from a saturated or failing disk? syncing logs?
With that said i am surprised people are having responsiveness issues under full load, are you sure you weren’t running out of memory and relying heavily on swapping?
100% agree. Desktop should always be a strong priority for the cpu.
One of my biggest frustrations with Linux. You are right. If I have something that works out of the box on windows but requires hours of research on Linux to get working correctly, it’s not an incentive to learn the complexities of Linux, it’s an incentive to ditch it. I’m a hobbyist when it comes to Linux but I also have work to do. I can’t be constantly ducking around with the OS when I have things to build.
I see what you mean but I feel like it’s more on the distro mainters to set niceness and prioritize the UI while under load.
What do you even mean as serious contender? I’ve been using Linux for almost 15 years without an issue on CPU, and I’ve used it almost only on very modest machines. I feel we’re not getting your whole story here.
On the other hand whenever I had to do something IO intensive on windows it would always crawl in these machines
You are getting the whole story - not sure what it is you think is missing. But I mean a serious desktop contender has to take UX seriously and have things “just work” without any custom configuration or tweaking or hacking around. Currently when I compile on Windows my browser and other programs “just works” while on Linux, the other stuff is choppy and laggy.
Wasn’t CFS replaced in 6.6 with EEDVF?
I have the 6.6 on my desktop, and I guess the compilations don’t freeze my media anymore, though I have little experience with it as of now, need more testing.
The Linux kernel uses the CPU default scheduler, CFS,
Linux 6.6 (which recently landed on Debian) changed the scheduled to EEVDF, which is pretty widely criticized for poor tuning. 100% busy which means the scheduler is doing good job. If the CPU was idle and compilation was slow, than we would look into task scheduling and scheduling of blocking operations.
Responsiveness for typical everyday usage is one of the main scenarios kernels like Zen/Liquorix and their out of the box scheduler configurations are meant to improve, and in my experience they help a lot. Maybe give them a go sometime!
Edit: For added context, I remember Zen significantly improving responsiveness under heavy loads such as the one OP is experiencing back when I was experimenting with some particularly computationally intensive tasks
https://github.com/zen-kernel/zen-kernel/wiki/Detailed-Feature-List
That’s the reason I installed Zen too and use it as the default. While Zen is meant to improve responsiveness of interactive usage on the system, it comes at a price. The overall performance might decrease and it should require more power. But if someone needs to solve the problem of the OP (need to work on the computer while under heavy load), then Zen is probably the right tool. Some distributions have the Zen Kernel in their repository and the install process is straightforward.
Very good points, it’s all trade-offs at the end of the day. I’ve always found them more than worth it myself for non server workloads, but as always YMMV.
nice +5 cargo buildnice is a program that sets priorities for the CPU scheduler. Default is 0. Goes from -19, which is max prio, to +19 which is min prio.
This way other programs will get CPU time before cargo/rustc.
So the better approach would be to spawn all desktop and base GUI things with
nice -18or something?No. This will wreak havoc. At most at -1 but I’d advise against that. Just spawn the lesser-prioritised programs with a positive value.
Could you elaborate?
Critical operating system tasks run at -19. If they don’t get priority it will create all kinds of problems. Audio often runs below 0 as well, at perhaps -2, so music doesn’t stutter under load. Stuff like that.
Ok, nice. Do you know what other undefined processes are spawned with?
Default is 0. Also, processes inherit the priority of their parent.
This is another reason why starting the desktop environment as a whole with a different prio won’t work: the compiler is started as a child of the editor or shell which is a child of the DE so it will also have the changed prio.
Damn… thanks thats complicated
It’s more of a workaround than a solution. I don’t want to have to do this for every intensive program I run. The desktop should just be responsive without any configuration.
You could give your compiler a lower priority instead of upping everything else.
I’d still need to lower the priority of my C++ compiler or whatever else intensive stuff I’d be running. I would like a general solution, not a patch just for running my Rust compiler.
How do you expect the system to know what program is important to you and which isn’t?
The windows solution is to switch tasks very often and to do a lot of accounting to ensure fair distribution. This results in a small but significant performance degradation. If you want your system to perform worse overall you can achieve this by setting the default process time slice value very low - don’t come back complaining if your builds suddently take 10-20% longer though.
The correct solution is for you to tell the system what’s important and what is not so it can do what you want properly.
You might like to configure and use the auto nice deamon: https://and.sourceforge.net/
How do you expect the system to know what program is important to you and which isn’t?
Hmm
The windows solution is to switch tasks very often and to do a lot of accounting to ensure fair distribution.
Sounds like you have a good idea already!
Yes, this is a bad solution. No program should have that privilege, it needs to be an allowlist and not a blocklist.
You could try using nice to give the rust compiler less priority (higher number) for scheduling.
This seems too complicated if I need to do that for other programs as well.
You can just alias to do this in the programs you do use
Sure, the first time you won’t have this enabled, but after that it just works.
The System76 scheduler helps to tune for better desktop responsiveness under high load: https://github.com/pop-os/system76-scheduler I think if you use Pop!OS this may be set up out-of-the-box.
I distro hop occasionally but always find myself coming back to popos. There are so many quality of life improvements that seem small but make all the difference.
Lots of bad answers here. Obviously the kernel should schedule the UI to be responsive even under high load. That’s doable; just prioritise running those over batch jobs. That’s a perfectly valid demand to have on your system.
This is one of the cases where Linux shows its history as a large shared unix system and its focus as a server OS; if the desktop is just a program like any other, who’s to say it should have more priority than Rust?
I’ve also run into this problem. I never found a solution for this, but I think one of those fancy new schedulers might work, or at least is worth a shot. I’d appreciate hearing about it if it does work for you!
Hopefully in a while there are separate desktop-oriented schedulers for the desktop distros (and ideally also better OOM handlers), but that seems to be a few years away maybe.
In the short term you may have some success in adjusting the priority of Rust with nice, an incomprehensibly named tool to adjust the priority of your processes. High numbers = low priority (the task is “nicer” to the system). You run it like this:
nice -n5 cargo build.Obviously the kernel should schedule the UI to be responsive even under high load.
Obviously… to you.
This is one of the cases where Linux shows its history as a large shared unix system and its focus as a server OS; if the desktop is just a program like any other,
Exactly.
Obviously… to you.
No. I’m sorry but if you are logged in with a desktop environment, obviously the UI of that desktop needs to stay responsive at all times, also under heavy load. If you don’t care about such a basic requirement, you could run the system without a desktop or you could tweak it yourself. But the default should be that a desktop is prioritized and input from users is responded to as quickly as possible.
This whole “Linux shouldn’t assume anything”-attitude is not helpful. It harms Linux’s potential as a replacement for Windows and macOS and also just harms its UX. Linux cannot ever truly replace Windows and macOS if it doesn’t start thinking about these basic UX guarantees, like a responsive desktop.
This is one of the cases where Linux shows its history as a large shared unix system and its focus as a server OS; if the desktop is just a program like any other,
Exactly.
You say that like it’s a good thing; it is not. The desktop is not a program like any other, it is much more important that the desktop keeps being responsive than most other programs in the general case. Of course, you should have the ability to customize that but for the default and the general case, desktop responsiveness needs to be prioritized.
Even for a server, the UI should always be priority. If you’re not using the desktop/UI, what’s the harm?
When you do need to remote into a box, it’s often when shit’s already sideways, and having an unresponsive UI (or even a sluggish shell) gets old.
A person interacting with a system needs priority.
I meant, obviously in the sense that Windows and macOS both apparently already do this and that it’s a desirable property to have, not that it’s technically easy.
“The kernel runs out of time to solve the NP-complete scheduling problem in time.”
More responsiveness requires more context-switching, which then subtracts from the available total CPU bandwidth. There is a point where the task scheduler and CPUs get so overloaded that a non-RT kernel can no longer guarantee timed events.
So, web browsing is basically poison for the task scheduler under high load. Unless you reserve some CPU bandwidth (with cgroups, etc.) beforehand for the foreground task.
Since SMT threads also aren’t real cores (about ~0.4 - 0.7 of an actual core), putting 16 tasks on a 16/8 machine is only going to slow down the execution of all other tasks on the shared cores. I usually leave one CPU thread for “housekeeping” if I need to do something else. If I don’t, some random task is going to be very pleased by not having to share a core. That “spare” CPU thread will be running literally everything else, so it may get saturated by the kernel tasks alone.
nice +5is more of a suggestion to “please run this task with a worse latency on a contended CPU.”.(I think I should benchmark make -j15 vs. make -j16 to see what the difference is)
That’s all fine, but as I said, Windows seems to handle this situation without a hitch. Why can Windows do it when Linux can’t?
Also, it sounds like you suggest there is a tradeoff between bandwidth and responsiveness. That sounds reasonable. But shouldn’t Linux then allow me to easily decide where I want that tradeoff to lie? Currently I only have workarounds. Why isn’t there some setting somewhere to say “Yes, please prioritise responsiveness even if it reduces bandwidth a little bit”. And that probably ought to be the default setting. I don’t think a responsive UI should be questioned - that should just be a given.
You’re right of course. I think the issue is that Linux doesn’t care about the UI. As far as it is concerned GUI is just another program. That’s the same reason you don’t have things like ctrl-alt-del on Linux.
To be fair, there should be some heuristics to boost priority of anything that has received input from the hardware. (a button click e.g.) The no-care-latency jobs can be delayed indefinitely.
Why can Windows do it when Linux can’t?
Windows lies to you. The only way they don’t get this problem is that they are reserving some CPU bandwidth for the UI beforehand. Which explains the 1-2% y-cruncher worse results on windows.
If that’s the solution to the problem, it’s a good solution. Linux ought to do the same thing, cause none of the suggestions in this thread have worked for me.
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nohz_fullconfusingly also helps with power usage… if the cpu doesn’t have anything to run, no point waking it up with a scheduler-tick IPI… but also no point trying to run the scheduler if a core is peaking with a single task… Withnohzthe kernel overheard basically ceases to exist for a task while the it is running. (Thought the overhead just moves to non-nohz cpu cores)
I agree that UI should always take priority. I shouldn’t have to do anything to guarantee this.
I have HZ_1000, tickless kernel with
nohz_fullset up. This all has a throughput/bandwidth cost (about 2%) in exchange for better responsiveness by default.But this is not enough, because the short burst UI tasks need near-zero wake-up latency… By the time the task scheduler has done its re-balancing the UI task is already sleeping/halted again, and this cycle repeats. So the nice/priorities don’t work very well for UI tasks. Only way a UI task can run immediately is if it can preempt something or if the system has a somewhat idle CPU to put it on.
The kernel doesn’t know any better which tasks are like this. The on-going
EEVDF,sched_extscheduler projects attempt to improve the situation. (EEVDFshould allow specifying the desired latency, whilesched_extwill likely allow tuning the latency automatically)
It really depends on your desktop. For instance gnome handles high CPU very well in my experience.
I would run your compiler in a podman container with a CPU cap.
Edit: it might be related to me using Fedora
I face similar issue when updating steam games although I think that’s related to disk read write
But either way, issues like these gonna need to be address before we finally hit the year of Linux desktop lol
Sounds like Kubuntu’s fault to me. If they provide the desktop environment, shouldn’t they be the ones making it play nice with the Linux scheduler? Linux is configurable enough to support real-time scheduling.
FWIW I run NixOS and I’ve never experienced lag while compiling Rust code.
I have a worrying feeling that if I opened a bug for the KDE desktop about this, they’d just say it’s a problem of the scheduler and that’s the kernel so it’s out of their hands. But maybe I should try?
The kde peeps are insanely nice so I guess you should try.
If you compile on windows server the same problem happens. The server is basically gone. So there seems to be some special scheduler configuration in windows client os.
I wonder if Linux should also provide server and desktop variants like Windows does, with different scheduler settings and such. The use cases are quite different after all, it’s kinda weird they use the same settings.
it’s typically up to the distribution to configure things like that, and many Linux distributions do come in both server and desktop or workstation variants like Ubuntu desktop vs Ubuntu server, or RHEL server vs RHEL Workstation
I can’t say how well they tune these things as I haven’t ran them personally, but they do exist.
So I just tried using
nice -n +19and it still lags my browser and my UI. So that’s not even a good workaround.Is your browser Firefox?
What kind of storage devices do you have? NVMe?
Did you check with tools likeiotopto see if something is going on IO wise?You assumed that the problem is caused by the CPU being utilized at 100%.
This may not be the case.A lot of us don’t run a DE at all. I myself use Awesome WM.
For non-tilers, Openbox with some toolbar would be the ideal setup.I mention this because we (non-DE users) would have no experience with some funky stuff like a possible KDE indexer running in the background killing IO performance and thrashing buffered/cached memory.
Also, some of us run firefox with
eatmydatabecause we hate fsync 🤨Neither KDE nor Gnome is peak Desktop Linux experience.
Ubuntu and its flavors is not peak distro experience either.If you want to try Desktop Linux for real, you will need to dip your toes a little bit deeper.
Yes Firefox, yes NVMe. No, there is no IO happening and again, sitting at relatively low memory usage. I was not running anything else than the compiler, my editor and Firefox. I’m fairly confident the CPU usage is the culprit as memory usage is not severely affected and disk usage by the compiler should be pretty minimal (and I don’t see how disk usage would make Firefox slow if there’s still plenty of RAM available).
Neither KDE nor Gnome is peak Desktop Linux experience. Ubuntu and its flavors is not peak distro experience either.
If you want to try Desktop Linux for real, you will need to dip your toes a little bit deeper.
I’ve heard much of the opposite - KDE is touted as an easy-to-use desktop and Ubuntu is largely a popular “just works” distro. And honestly that has been my primary experience. Mostly everything works, but there are some hiccups here and there like the problem I posted about in this thread.
What alternative would you suggest?
What alternative would you suggest?
A, rolling release first, distro (e.g. Arch or Void) with no DE installed.
But you’re probably not ready for that.
For me, a terminal and Firefox are the only GUI apps really needed. mpv too if it counts.
But I’m someone who has been running Arch+AwesomeWM for ~15 years ago (been using Arch for even longer). So I probably can’t meaningfully put myself in new users’ shoes.
Firefox on my raspberry pi grinds the thing to a halt, so I created a shortcut:
systemd-run --scope -p MemoryLimit=500M -p CPUQuota=50% firefox-esr
You say it doesn’t top out on memory, so you don’t need the -p MemoryLimit=500M parameter. Set your compiler CPUQuota to maybe 80%, or whatever you can work out with trial and error.
Found this b for your problem of limiting one specific program such as rust compiler: https://askubuntu.com/questions/1367612/how-can-i-limit-the-cpu-and-ram-usage-for-a-process
I don’t really want to limit the Rust compiler. If I leave my computer running while I take a break, I don’t want it to artificially throttle the compiler. I just want user input and responsiveness of open windows to take priority over the compiler.
OP most likely wants the opposite for the compiler…
All the comments here are great. One other suggestion I didn’t see: use chrt to start the build process with the sched_batch policy. It’s lower than sched_other, which most processes will be in, so the compilation processes should be bumped off the CPU for virtually everyone else
