this post was submitted on 26 Mar 2024
638 points (96.4% liked)
linuxmemes
21936 readers
2038 users here now
Hint: :q!
Sister communities:
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 users for any reason. This includes using blanket terms, like "every user of thing".
- Don't get baited into back-and-forth insults. We are not animals.
- 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, <loves/tolerates/hates> systemd, 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 remove France.
founded 2 years ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
I manage a machine that runs both media transcodes and some video game servers.
The video game servers have to run in real-time, or very close to it. Otherwise players using them suffer noticeable lag.
Achieving this at the same time that an ffmpeg process was running was completely impossible. No matter what I did to limit ffmpegs use of CPU time. Even when running it at lowest priority it impacted the game server processes running at top priority. Even if I limited it to one thread, it was affecting things.
I couldn't understand the problem. There was enough CPU time to go around to do both things, and the transcode wasn't even time sensitive, while the game server was, so why couldn't the Linux kernel just figure it out and schedule things in a way that made sense?
So, for the first time I read up on how computers actually handle processes, multi-tasking and CPU scheduling.
As FFMPEG is an application that uses ALL available CPU time until a task is done, I came to the conclusion that due to how context switching works (CPU cores can only do one thing, they just switch out what they do really fast, but this too takes time) it was causing the system to fall behind on the video game processes when the system was operating with zero processing headroom. The scheduler wasn't smart enough to maintain a real-time process in the face of FFMPEG, which would occupy ALL available cycles.
I learned the solution was core pinning. Manually setting processes to run on certain cores of the CPU. I set FFMPEG to use only one core, since it doesn't matter how fast it completes. And I set the game processes to use all but that one core, so they don't accidentally end up queueing for CPU time on a core that doesn't have the headroom to allow the task to run within a reasonable time range.
This has completely solved the problem, as the game processes and FFMPEG no longer wait for CPU cycles in the same queue.
This reminded me of how I disabled processor cores in Process Lasso for programs