Benchmarkng MsgPack vs JSON in Rust

After implementing MessagePack in Rust for Python and comparing serialized MessagePack versus JSON for a HyperLogLog data structure, I wanted to check the performance of the two.

Not needing PyO3 for this one, I wrote a straightforward main.rs with a few functions for testing ser/de for both formats:

#![feature(test)]
extern crate test;
// ...

#[bench]
pub fn ser_bytes(b: &mut test::Bencher) {
    let hll = HyperLogLog::<String>::new_from_keys(0.01, 123, 456);

    b.iter(|| {
        rmp_serde::to_vec(&hll).unwrap();
    });
}

#[bench]
pub fn ser_str(b: &mut test::Bencher) {
    let hll = HyperLogLog::<String>::new_from_keys(0.01, 123, 456);

    b.iter(|| {
        let _json = serde_json::to_string(&hll).unwrap();
    });
}

// Corresponding deserializing functions omitted

I then tested the four functions with cargo bench:

running 4 tests
test de_bytes  ... bench:       5,594 ns/iter (+/- 1,906)
test de_str    ... bench:      18,532 ns/iter (+/- 9,107)
test ser_bytes ... bench:      24,962 ns/iter (+/- 15,104)
test ser_str   ... bench:      18,363 ns/iter (+/- 3,592)

Based on this, it appears that MessagePack deserializes at 30% the time of JSON but serializes at 135%.