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by exikyut 1891 days ago
A question: I tried poking around with `tc` (qdisc) a while back to limit speed and emulate latency, and I found the implementation seemed to simulate delay by waiting a bunch of time then dumping all the data at once, for example if I asked for 5s of latency I'd be sitting at 0 bytes/sec for 5 seconds then it'd be like INCOMING and I'd get a giant pile of data all at once.

I do absolutely have horrendously little networking experience :) so I was probably fiddling with the knobs wrong (and fiddling with wrong expectations from the mechanics), but I didn't see any tunables for ramp-up et al.

For a while I've been idly curious how to iterate on applications that need to respond favorably to everything from 10Gbps and "what latency?" to flaky 3.5G with "give up" latency and worse jitter. At the end of the day I know I need real networks to play with, but I've been curious what software will get me the closest approximation in terms of microsecond-to-microsecond network behavior.

TBH this question is me being somewhat lazy :) - I'm not yet ready to start working on the above ideas, so I'm yet to actually sit down and do some basic prerequisite research... but I thought I'd jump on the opportunity to ask while I could.
1 comments
sporksmith 1891 days ago
Sorry, I'm not well versed in the network model; most of my work has been on the new ptrace-based syscall interposition. That sure sounds like a bug, though.

We recently added a discussion section to Shadow's GH repo: https://github.com/shadow/shadow/discussions. That'd be a good place for your questions. More knowledgeable folks are pretty responsive there, but aren't on HN :)

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exikyut 1891 days ago
Apologies for the ambiguity and lack of context - to clarify, I fiddled around with raw tc/qdisc (part of Linux's network stack) a while back, and was wondering if Shadow had more accurate timing simulation.

The discussion section sounds like exactly the place to follow up on this sort of thing, thanks for the reference. (Once I verify what I'm looking for is actually exotic :P)

Thanks for replying!

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