- cross-posted to:
- linux@lemmy.ml
- cross-posted to:
- linux@lemmy.ml
To get started with the real-time kernel for Ubuntu 24.04, check out the official documentation. One thing to keep in mind if you’re an NVIDIA GPU user is that the real-time Ubuntu kernel does not support the proprietary NVIDIA graphics drivers.
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You can just enable all of these features on any 6.8+ kernel. You don’t need Ubuntu Pro.
No, it will no radically improve your gaming performance, but it will definitely increase your energy bill.
Why would it increase your energy bill?
I guess, the governor is set to performance for a realtime kernel to work properly, thus the CPU consumes more power.
In modern processors, using performance can save power. By only powering up one core for a little while, even though it’s at a higher clock speed, some CPUs save energy by going back to sleep as soon as possible.
In my own experiments, powersave often did the opposite, keeping six or seven cores moderately active with light usage (because of the low clock speeds) and using more power than when I used performance.
Real life will vary by CPU and motherboard, of course.
Partially, but the shift is more in the amount of power required to constantly serve interrupts. That’s essentially what these flags enable. Where previously the kernel would be more lax about scheduling such things, this let’s all those interrupts off the chain. More interrupts = more power draw. The ARM and AMD extensions mean to reduce that in a meaningful way, though.
Can somebody explain real time kernel as if I am a golden retriever ?
Music recording? Idk
Yeah that’s exactly one of the niche use cases, like using a midi keyboard, though using a low latency kernel like Linux Zen would be more than enough for most users.
Who a good boy? You a good boy!
Basically tasks have a tight window of execution latency guarantee (although they can exceed that as Linux is not a deterministic hard realtime kernel)
This means potentially lower performance and other losses but it provides very low latency, which is useful for some tasks that need low latency due to their nature like high quality professional audio
An alternative definition: a real-time system is a system where the correctness of the computation depends on a deadline. For example, if I have a drone checking “with my current location + velocity will I crash into the wall in 5 seconds?”, the answer will be worthless if the system responds 10 seconds later.
A real-time kernel is an operating system that makes it easier to build such systems. The main difference is that they offer lower latency than a usual OS for your one critical program. The OS will try to give that program as much priority as it wants (to the detriment of everything else) and immediately handle all signals ASAP (instead of coalescing/combining them to reduce overhead)
Linux has real-time priority scheduling as an optional feature. Lowering latency does not always result in reduced overhead or higher throughout. This allows system builders to design RT systems (such as audio processing systems, robots, drones, etc) to utilize these features without annoying the hell out of everyone else.
So, contrary to what it seems a single CPU core can only execute a single “thing” at a time. Modern operating systems do something called “preemptive multitasking” to give the illusion that more than one things are running at a time. The OS will start your task, then after a while save its state and start another task running, then switch back. It does this fast enough that each job seems to be running concurrently.
Now if you’re running on a RaspberryPI your program might be waiting for input from a GPIO pin. And when you get that input you want to turn on some switch. Maybe an important switch. BUT It could be that your application is in the “paused” state when that pin gets input which will cause a delay between when the pin is trying to send you input and when you actually process it.
A real-time OS minimizes such delays (latency) so that you can respond quickly.
I guess i am still skipping on how real time kernel address the pause? it just never pauses or it no longer needs to be paused?
as a side note, is this similar technology they use in high precision manufacturing?
Think of it like a club with a max capacity of 10 people, where some people have VIP cards. If a person with a VIP card wants to get into the club, the bouncer will kick out one of the people inside that doesn’t have a VIP card to make space for them.
For a more technical explanation:
There are several processors on computers and each can be in use by 1 process at a time. Different processes can get different amounts of time based on their priority (called niceness in Linux) and they’ll be removed from the processor once their time is up until their next share of time.
On a real-time kernel some processes are marked as real-time (certain range of niceness values, can’t remember the exact range). If a process that is real-time says it needs some processor time, a process that isn’t real-time that’s currently running will be immediately ripped off the processor to make room for the real-time process.
I guess i am still skipping on how real time kernel address the pause? it just never pauses or it no longer needs to be paused?
When hardware has data ready for a program it generates an interrupt that lets the OS know that there is data ready for an application. My understanding is that real-time OSs give high priority to interrupts so that they’re processed quickly - usually within a fixed period of time (e.g. they may have a max time between interrupt and processing).
as a side note, is this similar technology they use in high precision manufacturing?
In those cases it may be more likely they use a micro-controller that doesn’t run any OS at all - at least not a multi-tasking one. If you’re just running a single program you don’t need to worry about latency due to other applications running.
Why are we monetizing a kernel flag?
