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.

  • JATth@lemmy.world
    4·
    5 months ago

    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_full set 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_ext scheduler projects attempt to improve the situation. (EEVDF should allow specifying the desired latency, while sched_ext will likely allow tuning the latency automatically)