this post was submitted on 16 Feb 2024
987 points (99.2% liked)
linuxmemes
21304 readers
1383 users here now
Hint: :q!
Sister communities:
- LemmyMemes: Memes
- LemmyShitpost: Anything and everything goes.
- RISA: Star Trek memes and shitposts
Community rules (click to expand)
1. Follow the site-wide rules
- Instance-wide TOS: https://legal.lemmy.world/tos/
- Lemmy code of conduct: https://join-lemmy.org/docs/code_of_conduct.html
2. Be civil
- Understand the difference between a joke and an insult.
- Do not harrass or attack members of the community for any reason.
- Leave remarks of "peasantry" to the PCMR community. If you dislike an OS/service/application, attack the thing you dislike, not the individuals who use it. Some people may not have a choice.
- Bigotry will not be tolerated.
- These rules are somewhat loosened when the subject is a public figure. Still, do not attack their person or incite harrassment.
3. Post Linux-related content
- Including Unix and BSD.
- Non-Linux content is acceptable as long as it makes a reference to Linux. For example, the poorly made mockery of
sudoin Windows. - No porn. Even if you watch it on a Linux machine.
4. No recent reposts
- Everybody uses Arch btw, can't quit Vim, and wants to interject for a moment. You can stop now.
Please report posts and comments that break these rules!
Important: never execute code or follow advice that you don't understand or can't verify, especially here. The word of the day is credibility. This is a meme community -- even the most helpful comments might just be shitposts that can damage your system. Be aware, be smart, don't fork-bomb your computer.
founded 1 year ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
I find this a highly interesting problem. How do you measure how much CPU time a program needs? The OS has ceded its control of the CPU to the program. Does it just look at the clock after it’s in charge again to derive a program’s load?
While we’re at it: How does the OS even yank the CPU away from the currently running process?
Well behaving programs give control back to the kernel as soon as they are done with what they are doing. If they don't the control is forcefully taken away after some assigned time.
It looks something like this:
Something happens – e.g. a key is pressed – a process waiting for this event is woken up and gets e.g. 100ms to do it stuff. If it can handle the key press in 50ms, kernel notes it used 50 ms of CPU time and can give control to another process waiting for an event or busy with other work. If the key press triggered long computation the process won't be done in 100ms, the kernel notes it used 100ms of CPU time and gives control to other processes with pending events or busy with other work.
After one second the kernel may have noted:
Process A: used 50ms, then nothing, then 100ms, another 100ms and another 100ms
Process B: was constantly busy doing something, so it got allocated 6 * 100ms in that one second
Process C: just got one event and handled it in 50ms
Process D: was not waken at all
So total of 1000ms was used – the CPU was 100% busy
Of that 60% was process B, 35% process A and 5% process C.
And then that information is read from the kernel by top and displayed.
Interrupts. CPU has means triggering and interrupt at a specific time. Interrupt means that CPU stops what it is doing and runs selected piece of kernel code. This piece of kernel code can save the current state of user process execution and do something else or restore saved execution of another process.