buffered randomness throughput benchmarks

randpool_test.go

package main

import (
	"bufio"
	"crypto/rand"
	"fmt"
	"testing"
)

func BenchmarkRandReads(b *testing.B) {
	const size = 16 // assume we need 16 bytes of entropy per seed operation
	var dst [size]byte

	b.Run("buffer=none", func(b *testing.B) {
		b.SetBytes(size)
		for i := 0; i < b.N; i++ {
			_, _ = rand.Read(dst[:])
		}
	})

	bufSizes := []int{128, 256, 512, 1024, 2048, 4096}
	for _, bs := range bufSizes {
		b.Run(fmt.Sprintf("buffer=%d", bs), func(b *testing.B) {
			b.SetBytes(size)
			bufReader := bufio.NewReaderSize(rand.Reader, bs)
			for i := 0; i < b.N; i++ {
				_, _ = bufReader.Read(dst[:])
			}
		})
	}
}

results.txt

BenchmarkRandReads/buffer=none           2859973               411.0 ns/op        38.93 MB/s
BenchmarkRandReads/buffer=128           22197540                54.26 ns/op      294.90 MB/s
BenchmarkRandReads/buffer=256           37927024                31.17 ns/op      513.39 MB/s
BenchmarkRandReads/buffer=512           38238277                31.08 ns/op      514.84 MB/s
BenchmarkRandReads/buffer=1024          37930171                30.64 ns/op      522.23 MB/s
BenchmarkRandReads/buffer=2048          38966889                30.62 ns/op      522.45 MB/s
BenchmarkRandReads/buffer=4096          39039996                30.33 ns/op      527.45 MB/s

all buffering was removed from crypto/rand in https://go-review.googlesource.com/c/go/+/390038, however it appears to add significant benefit to throughput when doing many small sequential reads.