How many system calls happen underneath if I were to broadcast to bunch of connected clients of my server? about tokio-uring

[Noah-Kennedy]

This is tokio-uring, not rio. If you have a question about this, I'm happy to answer it, but I am not familiar with the implementation details of rio.

[kant777]

@Noah-Kennedy Sorry, it was a copy/paste error and I haven't got any response from rio so my questions are generally the same and I slightly edited. would be great to know how tokio-uring can help? hope my question is generic enough if not please let me know

[Noah-Kennedy]

So, IO functions/methods in tokio-uring will push a SQE to the submission queue. In current releases, these operations are immediately submitted to the kernel, resulting in a syscall. On the master branch, we have implemented batching, and thus we will submit all operations in the queue if it becomes full when constructing an op, and will also submit all operations to the kernel before parking, so system calls tend to be pretty efficiently amortized across operations.

I'd also like to get hooks into tokio at some point to allow us to submit operations periodically when tokio runs it's internal maintenance routine.

[kant777]

@Noah-Kennedy Got it, so I need to use master, because if it submits a syscall for every operation then that defeats the purpose of io_uring altogether. I am glad to hear that batching is implemented internally but does it submit to kernel only when the buffer is full? what if the buffer isn't full? is there any timer? if not, then why not let users batch their syscalls and provide a function like submit_all?

[Noah-Kennedy]

If we attempt to push an operation but the buffer is full, we submit all operations in the buffer to make space and then push.

There is no timer for periodic dispatch. This is better implemented by hooking into the maintenance loop of tokio.

Allowing users to control their own batching is something I'd like to get implemented soon, alongside some newer APIs that give more fine-grained control of operation submission.

[kant777]

Got it, But again what if the buffer isn't full? it will stay in queue forever? I didn't mean to say timer in isolation but a combination of buffer size and the timer or let the user take care of it all!

[Noah-Kennedy]

Currently on master, when there isn't work to do (ie the system parks), it will flush the squeue and submit. This isn't released yet because this isn't exactly ideal; we need to get hooks into tokio to periodically flush the queue every X task polls (I forget how often the tokio maintenance loop runs).