xxd `which hexyl` > /dev/null 0.12s user 0.09s system 99% cpu 0.219 total
hexdump `which hexyl` > /dev/null 0.19s user 0.05s system 91% cpu 0.256 total
hexyl `which hexyl` > /dev/null 1.69s user 0.39s system 95% cpu 2.175 total hyperfine './target/release/hexyl ./target/release/hexyl' 'xxd ./target/release/hexyl' 'hexdump ./target/release/hexyl'
Benchmark #1: ./target/release/hexyl ./target/release/hexyl
Time (mean ± σ): 1.529 s ± 0.028 s [User: 1.476 s, System: 0.050 s]
Range (min … max): 1.491 s … 1.581 s 10 runs
Benchmark #2: xxd ./target/release/hexyl
Time (mean ± σ): 70.5 ms ± 0.5 ms [User: 68.0 ms, System: 1.2 ms]
Range (min … max): 69.5 ms … 72.3 ms 41 runs
Benchmark #3: hexdump ./target/release/hexyl
Time (mean ± σ): 262.4 ms ± 2.8 ms [User: 260.1 ms, System: 1.5 ms]
Range (min … max): 259.8 ms … 268.8 ms 11 runs
Summary
'xxd ./target/release/hexyl' ran
3.72 ± 0.05 times faster than 'hexdump ./target/release/hexyl'
21.70 ± 0.43 times faster than './target/release/hexyl ./target/release/hexyl'
Yes, it's a shame. But I don't think there is too much we can do about it. We have to print much more to the console due to the ANSI escape codes and we also have to do some conditional checks ON EACH BYTE in order to colorize them correctly. Surely there are some ways to speed everything up a little bit, but in the end I don't think its a real issue. Nobody is going to look at 1MB dumps in a console hex viewer (that's 60,000 lines of output!) without restricting it to some region. And if somebody really wants to, he can probably spare 1.5 seconds to wait for the output :-)
A few extra comparisons and output for each byte shouldn't be that much slower; fortunately the function of this program is extremely well-defined, so we can calculate some estimates. Assuming a billion instructions per second, taking ~1.5s to hexdump ~1 million bytes means each byte is consuming ~1500 instructions to process. In reality the time above is probably on a faster CPU, so that number maybe 2-3x more. That is a shockingly high number just to split a byte into two nybbles (expected to be 1-3 instructions), convert the nybbles into ASCII (~3 instructions), and decide on the colour (let's be very generous and say ~100 instructions.)
The fact that the binary itself is >1MB is also rather surprising, especially given that the source (not familiar with Rust, but still understandable) seems quite small and straightforward.
Did rust become less dependent on allocator performance, or did system allocators improve enough? IIRC glibc malloc has improved a lot over the last few years, particularly for multithreaded use, but I don't know about windows / macOS.
So, now that we have a stable way to let you use jemalloc, the right default for a systems language is to use the system allocator. If jemalloc makes sense for you, you can still use it, but if not, you save a non-significant amount of binary size, which matters to a lot of people. See the parent I originally replied to for an example of a very common response when looking at Rust binary sizes.
It's really more about letting you choose the tradeoff than it is about specific improvements between the allocators.
(If it's spending a lot of time in Rust's format function you could also use a (or the same) lookup table to convert to hex/dec/oct.)
Edit: Turns out to be about 22% overhead, see https://github.com/sharkdp/hexyl/pull/23. Also it was 2 strings per byte, not 1.
Benchmark #1: hexyl $(which hexyl)
Time (mean ± σ): 169.8 ms ± 8.2 ms [User: 152.5 ms, System: 17.1 ms]
Range (min … max): 162.2 ms … 189.1 ms 16 runs
Benchmark #2: hexdump -C $(which hexyl)
Time (mean ± σ): 188.5 ms ± 4.4 ms [User: 186.2 ms, System: 2.2 ms]
Range (min … max): 184.1 ms … 198.2 ms 14 runs
Benchmark #3: xxd $(which hexyl)
Time (mean ± σ): 72.8 ms ± 2.7 ms [User: 71.9 ms, System: 1.1 ms]
Range (min … max): 71.0 ms … 87.8 ms 40 runshttps://github.com/sjmulder/hxl
Most of the improvement came from not using printf, fputs, and putchar in favour of operating directly on an array for the line that can be fwritten in one call.