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How do you handle real-time thread priorities and CPU affinity? I work in soft real-time software as well (feedback control for humanoid robots) and I've been w

by dljsjr 9y ago

How do you handle real-time thread priorities and CPU affinity? I work in soft real-time software as well (feedback control for humanoid robots) and I've been wanting to play around with Rust for real-time programming for a while. Given that your workload is parallel I would imagine CPU pinning is pretty important for making your deadlines. Since my current job involves maintaining a bunch of natively bridged code to add real-time scheduling to a non-realtime environment (Java) I don't wanna muck around with it until the language itself adds the stuff needed to the native API. I've been watching this RFC[1] for years waiting for some notion of progress of support for this in the language itself. Doesn't seem to be a lot of focus on it right now. [1]: https://github.com/rust-lang/rfcs/issues/819 https://github.com/rust-lang/rfcs/issues/819

rapsey 9y ago
This crate provides the functionality: https://github.com/Elzair/core_affinity_rs https://github.com/Elzair/core_affinity_rs It takes a couple of seconds to add this crate to your project. I don't see what the problem is?
- dljsjr 9y ago
  Well for one, that crate's first commit is from September from this year so it's quite new and I didn't know about it. That's the sort of information I was looking for with my question. Secondly, though, while it handles affinity it still doesn't handle priority.
  - pornel 9y ago
    If you know how to do that in C, you can call the same functions from Rust (you'll find them in libc crate or you'll need `bindgen` to convert a C header to Rust). The Rust ecosystem is still young, but on the upside maintainers are active and keen to expand their crates, so there's a high chance they'll add the feature you need if you just ask.
    - dljsjr 9y ago
      From my understanding (and also mentioned by someone in the comments on the RFC I linked), while you can do things to the threads by just directly calling through to C, what you end up with is a thread that doesn't have all of the Rust runtime niceties set up on it correctly. I'm just waiting for a full featured version of this functionality to be available in the language, but I was also sort of curious to see what OP's solution to the problem was. And like I mentioned originally, my day job is to maintain code that does the same thing but for Java. I don't wanna have to maintain it in two languages even if one is just a pet project. Since Rust is billing itself as a systems language it makes sense that this will be a feature eventually, and I'm willing to wait patiently. It's not holding me back from anything, it's just a personal curiosity.
      - steveklabnik 9y ago
        Rust doesn’t really have much of a runtime; I’m not sure what niceties you’re thinkjg of :) (I also logged that you talked about this in the issue; even knowing people want this is useful; it’s probably not in std because nobody’s ever really argued they need it!)
        dljsjr 9y ago
        Thanks for taking the time to look at this Steve! I'm not super familiar with threading in Rust, I was just going off comments made in the RFC and what little research I had done at the time I started looking in to it. This was all a few years ago and I know the runtime used to be much heavier so my info could very well be out of date. I know that this is a feature that doesn't impact a large number of people, but for the people that do need it it's pretty important. Being able to do soft real-time threading inside of an RTOS environment like Xenomai or Linux w/ the preemptive kernel (RT) patch in combination with Rust's other safety-oriented features would be a huge boon for embedded developers I think.
        steveklabnik 9y ago
        Ah ha! So, looking at the issue, at that time, Rust did have a runtime, and green threads. Today, we don't, and just have OS threads. So that's where the miscommunication lies :)

by dljsjr 9y ago

rapsey 9y ago

This crate provides the functionality: https://github.com/Elzair/core_affinity_rs https://github.com/Elzair/core_affinity_rs It takes a couple of seconds to add this crate to your project. I don't see what the problem is?

dljsjr 9y ago
Well for one, that crate's first commit is from September from this year so it's quite new and I didn't know about it. That's the sort of information I was looking for with my question. Secondly, though, while it handles affinity it still doesn't handle priority.
- pornel 9y ago
  If you know how to do that in C, you can call the same functions from Rust (you'll find them in libc crate or you'll need `bindgen` to convert a C header to Rust). The Rust ecosystem is still young, but on the upside maintainers are active and keen to expand their crates, so there's a high chance they'll add the feature you need if you just ask.
  - dljsjr 9y ago
    From my understanding (and also mentioned by someone in the comments on the RFC I linked), while you can do things to the threads by just directly calling through to C, what you end up with is a thread that doesn't have all of the Rust runtime niceties set up on it correctly. I'm just waiting for a full featured version of this functionality to be available in the language, but I was also sort of curious to see what OP's solution to the problem was. And like I mentioned originally, my day job is to maintain code that does the same thing but for Java. I don't wanna have to maintain it in two languages even if one is just a pet project. Since Rust is billing itself as a systems language it makes sense that this will be a feature eventually, and I'm willing to wait patiently. It's not holding me back from anything, it's just a personal curiosity.
    - steveklabnik 9y ago
      Rust doesn’t really have much of a runtime; I’m not sure what niceties you’re thinkjg of :) (I also logged that you talked about this in the issue; even knowing people want this is useful; it’s probably not in std because nobody’s ever really argued they need it!)
      - dljsjr 9y ago
        Thanks for taking the time to look at this Steve! I'm not super familiar with threading in Rust, I was just going off comments made in the RFC and what little research I had done at the time I started looking in to it. This was all a few years ago and I know the runtime used to be much heavier so my info could very well be out of date. I know that this is a feature that doesn't impact a large number of people, but for the people that do need it it's pretty important. Being able to do soft real-time threading inside of an RTOS environment like Xenomai or Linux w/ the preemptive kernel (RT) patch in combination with Rust's other safety-oriented features would be a huge boon for embedded developers I think.
        steveklabnik 9y ago
        Ah ha! So, looking at the issue, at that time, Rust did have a runtime, and green threads. Today, we don't, and just have OS threads. So that's where the miscommunication lies :)