Improve siphash performance for longer data #27280
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r? @aturon (rust_highfive has picked a reviewer for you, use r? to override) |
Use `ptr::copy_nonoverlapping` (aka memcpy) to load an u64 from the byte stream. This is correct for any alignment, and the compiler will use the appropriate instruction to load the data. Use unchecked indexing. This results in a large improvement of throughput (hashed bytes / second) for long data. Maximum improvement benches at a 70% increase in throughput for large values (> 256 bytes) but already values of 16 bytes or larger improve. Introducing unchecked indexing is motivated to reach as good throughput as possible. Using ptr::copy_nonoverlapping without unchecked indexing would land the improvement some 20-30 pct units lower. We use a debug assertion so that the test suite checks our use of unchecked indexing.
Without this temporary variable, codegen improves slightly and less registers are spilled to the stack in SipHash::write.
If they are ordered v0, v2, v1, v3, the compiler can find just a few simd optimizations itself. The new optimization I could observe on x86-64 was using 128 bit registers for the v = key ^ constant operations in new / reset.
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Thank you! |
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Improve siphash performance for longer data Use `ptr::copy_nonoverlapping` (aka memcpy) to load an u64 from the byte stream. This is correct for any alignment, and the compiler will use the appropriate instruction to load the data. Also contains small tweaks that should benefit hashing short data too, both the commit that removes a variable and the autovectorization of the hash state initialization (in SipHash::reset). Benchmarks show that hashing longer data benefits for the improved word loading. Before (using benchmarks from the first commit in the PR): The before benchmark is a bit noisy. ``` test hash::sip::bench_bytes_4 ... bench: 41 ns/iter (+/- 0) = 97 MB/s test hash::sip::bench_bytes_7 ... bench: 49 ns/iter (+/- 2) = 142 MB/s test hash::sip::bench_bytes_8 ... bench: 42 ns/iter (+/- 4) = 190 MB/s test hash::sip::bench_bytes_a_16 ... bench: 57 ns/iter (+/- 14) = 280 MB/s test hash::sip::bench_bytes_b_32 ... bench: 85 ns/iter (+/- 74) = 376 MB/s test hash::sip::bench_bytes_c_128 ... bench: 278 ns/iter (+/- 33) = 460 MB/s test hash::sip::bench_long_str ... bench: 825 ns/iter (+/- 103) test hash::sip::bench_str_of_8_bytes ... bench: 151 ns/iter (+/- 66) test hash::sip::bench_str_over_8_bytes ... bench: 59 ns/iter (+/- 3) test hash::sip::bench_str_under_8_bytes ... bench: 47 ns/iter (+/- 56) test hash::sip::bench_u32 ... bench: 39 ns/iter (+/- 93) = 205 MB/s test hash::sip::bench_u32_keyed ... bench: 40 ns/iter (+/- 88) = 200 MB/s test hash::sip::bench_u64 ... bench: 54 ns/iter (+/- 96) = 148 MB/s ``` After: ``` test hash::sip::bench_bytes_4 ... bench: 41 ns/iter (+/- 3) = 97 MB/s test hash::sip::bench_bytes_7 ... bench: 48 ns/iter (+/- 0) = 145 MB/s test hash::sip::bench_bytes_8 ... bench: 35 ns/iter (+/- 1) = 228 MB/s test hash::sip::bench_bytes_a_16 ... bench: 45 ns/iter (+/- 1) = 355 MB/s test hash::sip::bench_bytes_b_32 ... bench: 60 ns/iter (+/- 0) = 533 MB/s test hash::sip::bench_bytes_c_128 ... bench: 161 ns/iter (+/- 5) = 795 MB/s test hash::sip::bench_long_str ... bench: 514 ns/iter (+/- 5) test hash::sip::bench_str_of_8_bytes ... bench: 44 ns/iter (+/- 0) test hash::sip::bench_str_over_8_bytes ... bench: 51 ns/iter (+/- 0) test hash::sip::bench_str_under_8_bytes ... bench: 52 ns/iter (+/- 6) test hash::sip::bench_u32 ... bench: 40 ns/iter (+/- 2) = 200 MB/s test hash::sip::bench_u32_keyed ... bench: 39 ns/iter (+/- 1) = 205 MB/s test hash::sip::bench_u64 ... bench: 36 ns/iter (+/- 1) = 222 MB/s ```
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Nice wins. |
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Awesome! Thanks! |
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Improve siphash performance for longer data
Use
ptr::copy_nonoverlapping(aka memcpy) to load an u64 from thebyte stream. This is correct for any alignment, and the compiler will
use the appropriate instruction to load the data.
Also contains small tweaks that should benefit hashing short data too,
both the commit that removes a variable and the autovectorization of
the hash state initialization (in SipHash::reset).
Benchmarks show that hashing longer data benefits for the improved word loading.
Before (using benchmarks from the first commit in the PR):
The before benchmark is a bit noisy.
After: