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Comment by TickleSteve | Hacker News Reader

Linux is general is not a real-time system, in that you cannot get deterministic response time from it.

For example I'm guessing it doesn't matter if one of your timers are a second late due to Linux deciding to swap a process out or prioritise some upgrade check but imagine if your time constraints were a lot tighter.

Similarly if you're attempting to track food on a conveyor belt and Linux decides to prioritise the file indexer on your filesystem... oops, a lettuce has been thrown on the floor.

Real-time operating systems exist for a reason.

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Our tolerance requirements for synchronicity are broad enough that we can tolerate blips like this... at the end of the day we are automating away some simple human interactions (ie; fry the fries or track the food), we aren’t performing surgery with these systems.

So far we’ve been satisfied with Linux (Ubuntu 18.04 to be exact) and it’s overall capabilities.

Also, don’t forget that cost at scale is a big factor... doing things perfectly but expensively is not profitable at 2k locations.

The point about real-time systems is not the your tolerance of 'blips' its about analysis of your worst-case timing requirements. This is what real-time control systems are all about.

Sure, you may be able to tolerate a 1 second 'blip'... how about ten seconds? a minute? do you know for sure how long Linux may put your process on hold for? Linux provides no guarantees at all.

It seems to me that what you are really creating is a traditional control system with web technologies and using the hype-of-the-day (i.e. edge computing) to justify it... with the corresponding increase in overhead and cycles.

This does not seem like a good solution to me, the only novelty here is the inappropriate use of technologies. i.e. you've managed to dig a tunnel with a spoon.

Seems like a very appropriate use of technology to me?

If they can get "good enough" results using Linux and running with technologies that the average developer is more likely to know, is it worth the investment in running a RTOS? Especially given running a RTOS will make any higher level app integration more difficult?

The benefit of running with Linux outweighs the risk of "lettuce on the floor", imo. Yes, there's probably overhead in terms of clock cycles, but there's also probably dramatically less overhead in terms of developer resources.. and when you're running off commodity hardware you can guess which overhead will cost more!

It would also be 'cheaper' to build a bridge using lego....

Correctness of the solution is important, otherwise we're just playing at being engineers.

To quote you:

> At some point, you will realise that your job is not to create an idol to the software-engineering gods but rather to have a working product.

> Does this product work? if so, its doing its job.

https://news.ycombinator.com/item?id=17824782

Have you worked with k8s yet? A lot of the things you bring up are addressed if k8s is used properly.

K8s has nothing to say about schedulability or real-time performance, its just not what it does. K8s is simply a way to coordinate containers, nothing to do with scheduling processes on this level.

Something like RTLinux however, would. (https://en.wikipedia.org/wiki/RTLinux)

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