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.
JATtho
joined 2 years ago
Cryptographic CSPRNG seed? No way I'm telling that.
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)
No, I definitely want it to use as many resources it can get.
taskset -c 0 nice -n+5 bash -c 'while :; do :; done' &
taskset -c 0 nice -n+0 bash -c 'while :; do :; done'
Observe the cpu usage of nice +5 job: it's ~1/10 of the nice +0 job. End one of the tasks and the remaining jumps back to 100%.
Nice'ing doesn't limit the max allowed cpu bandwidth of a task; it only matters when there is contention for that bandwidth, like running two tasks on the same CPU thread. To me, this sounds exactly what you want: run at full tilt when there is no contention.
"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 +5 is 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)
BTW. With clang lto'd kernel 6.9. When non-Arch get the buggy updates, We have already moved on.
cries silently So no sleep until I crash. Got it.
It tastes like banana? I'm in, I have been looking for bourbon that actually tastes like banana/pineaple...
I once helped a person with their computer. They complained the they cant save the their photos. Well, their onedrive was filled to brim with crap, while the local 1Tb disk was empty because they had zero idea how storage and folders work. I had to explain her there is literally 1000x more fast disk space available, so please dont save into onedrive.
Wayland has much more up-to-date graphics technologies behind it to put it simply.
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.