Nailgun: A Rust DNS performance testing client

https://leshow.github.io/post/nailgun/

by leshow • 5 years ago

45 10 5 years ago

leshow.github.io

bluejekyll• 5 years ago

It always makes me excited to see what people are doing with the trust-dns libraries. Thanks for your contributions to the project. It's very cool to see some performance testing tools like this coming to Rust.

leshow2• 5 years ago

Thank you for making such a great collection of libs!

zokier• 5 years ago

    in_flight: FxHashMap<u16, QueryInfo>

this makes me think of one possible micro-optimization: u16 is small and memory is cheap, so you could just have

    in_flight: [Option<QueryInfo>; 65536]

you might get away with not having the Option wrapper, depending on how your code works

anyways, fun project

Arnavion3• 5 years ago

It depends. `QueryInfo` is a struct of `std::time::Instant` and `usize`, which makes it 24 bytes on x86_64 Linux for example. So the `Store` type that contains it will become 64 Ki * 24B = 1.5 MiB larger, which will break if the `Store` is held on the stack in systems with small-enough thread stacks. In particular, the default stack size on Windows for the main thread is 1 MiB.

tialaramex3• 5 years ago

If you decide that you can't afford for it to live on the stack, you could use a Vec so that it lives on the heap but it's still a single pointer dereference to get the QueryInfo (or not) which is a similar value.

The nice thing about the stack is that it's warmer (more likely to be in cache), but this is less valuable for these larger sizes where the structure is too large to all fit in fast cache anyway.

Actually depending on how sparse the map is, that's a reason not to do this at all. I don't know what a FxHashMap is, but if you've got a u16 key and only a small number of entries in your map, some maps won't need more than a few cachelines to store that data, far smaller than the 1.5MB contemplated above.

Anyway with anything like this, measure three times, mark twice, cut once. If you don't have a performance problem, needn't do anything, if you do have a performance problem you need to measure it before you try to fix it.

Nailgun: A Rust DNS performance testing client

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