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#![feature(test)]
extern crate test;
use std::{
alloc::{alloc_zeroed, dealloc, Layout},
ptr::NonNull,
};
// AlignedBuffer is like a Box<[u8; N]> except that it is always N-byte aligned
struct AlignedBuffer<const N: usize>(NonNull<[u8; N]>);
impl<const N: usize> AlignedBuffer<N> {
fn layout() -> Layout {
Layout::from_size_align(N, N).unwrap()
}
fn new() -> Self {
let p = unsafe { alloc_zeroed(Self::layout()) } as *mut [u8; N];
Self(NonNull::new(p).unwrap())
}
fn buf(&mut self) -> &mut [u8; N] {
unsafe { self.0.as_mut() }
}
}
impl<const N: usize> Drop for AlignedBuffer<N> {
fn drop(&mut self) {
unsafe { dealloc(self.0.as_ptr() as *mut u8, Self::layout()) }
}
}
// Used to benchmark the throughput of getrandom in an optimal scenario.
// The buffer is hot, and does not require initialization.
#[inline(always)]
fn bench<const N: usize>(b: &mut test::Bencher) {
let mut ab = AlignedBuffer::<N>::new();
let buf = ab.buf();
b.iter(|| {
getrandom::getrandom(&mut buf[..]).unwrap();
test::black_box(&buf);
});
b.bytes = N as u64;
}
// Used to benchmark the throughput of getrandom is a slightly less optimal
// scenario. The buffer is still hot, but requires initialization.
#[inline(always)]
fn bench_with_init<const N: usize>(b: &mut test::Bencher) {
let mut ab = AlignedBuffer::<N>::new();
let buf = ab.buf();
b.iter(|| {
for byte in buf.iter_mut() {
*byte = 0;
}
getrandom::getrandom(&mut buf[..]).unwrap();
test::black_box(&buf);
});
b.bytes = N as u64;
}
// 32 bytes (256-bit) is the seed sized used for rand::thread_rng
const SEED: usize = 32;
// Common size of a page, 4 KiB
const PAGE: usize = 4096;
// Large buffer to get asymptotic performance, 2 MiB
const LARGE: usize = 1 << 21;
#[bench]
fn bench_seed(b: &mut test::Bencher) {
bench::<SEED>(b);
}
#[bench]
fn bench_seed_init(b: &mut test::Bencher) {
bench_with_init::<SEED>(b);
}
#[bench]
fn bench_page(b: &mut test::Bencher) {
bench::<PAGE>(b);
}
#[bench]
fn bench_page_init(b: &mut test::Bencher) {
bench_with_init::<PAGE>(b);
}
#[bench]
fn bench_large(b: &mut test::Bencher) {
bench::<LARGE>(b);
}
#[bench]
fn bench_large_init(b: &mut test::Bencher) {
bench_with_init::<LARGE>(b);
}
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