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any1 / neatvnc

A liberally licensed VNC server library with a clean interface
ISC License
126 stars 31 forks source link

Add continuous update support #95

Closed pH5 closed 2 months ago

pH5 commented 1 year ago

Support sending continuous framebuffer updates when requested via the EnableContinuousUpdates message.

any1 commented 1 year ago

The reason why I didn't implement this already is that with multiple in-flight buffer requests, you basically get continuous updates plus rudimentary congestion control. However, now that SO_SNDBUF has been set to a lower value, HOL blocking on the host should be taken care of, although buffer bloat somewhere in between is a possibility, I suppose.

Does this improve some performance metric for some clients? I suppose that some clients might not pipeline requests, but support continuous updates instead.

pH5 commented 1 year ago

I don't have any hard metrics, I just noticed support in the client. Let's bench this for now.

any1 commented 3 months ago

I've been looking into this a little bit closer lately and it turns out that clients generally don't pipeline their requests and those who do only keep a backlog of 2 or 3 requests.

It's probably easier to just add this extension than to go around adding 20 extra requests (because that's what's needed when the RTT is 300 ms) to every open source client out there.

It could also be argued that keeping a backlog of multiple requests isn't very robust because you don't know the frame rate or the latency.

This is an interesting read: https://github.com/TigerVNC/tigervnc/wiki/Development%3A-Latency

any1 commented 2 months ago

Thanks!