cryptocore: add urandom + randprefetch benchmarks

The benchmark that supported the decision for 512-byte
prefetching previously lived outside the repo.

Let's add it where it belongs so it cannot get lost.

1 files changed, 40 insertions, 0 deletions

diff --git a/internal/cryptocore/randsize_test.go b/internal/cryptocore/randsize_test.go
new file mode 100644
index 0000000..1db4745
--- /dev/null
+++ b/internal/cryptocore/randsize_test.go
@@ -0,0 +1,40 @@
+// +build go1.7
+
+// ^^^^^^^^^^^^ we use the "sub-benchmark" feature that was added in Go 1.7
+
+package cryptocore
+
+import (
+	"fmt"
+	"testing"
+)
+
+/*
+The troughput we get from /dev/urandom / getentropy depends a lot on the used
+block size. Results on my Pentium G630 running Linux 4.11:
+
+BenchmarkRandSize/16-2         	 3000000	       571 ns/op	  27.98 MB/s
+BenchmarkRandSize/32-2         	 3000000	       585 ns/op	  54.66 MB/s
+BenchmarkRandSize/64-2         	 2000000	       860 ns/op	  74.36 MB/s
+BenchmarkRandSize/128-2        	 1000000	      1197 ns/op	 106.90 MB/s
+BenchmarkRandSize/256-2        	 1000000	      1867 ns/op	 137.06 MB/s
+BenchmarkRandSize/512-2        	  500000	      3187 ns/op	 160.61 MB/s
+BenchmarkRandSize/1024-2       	  200000	      5888 ns/op	 173.91 MB/s
+BenchmarkRandSize/2048-2       	  100000	     11554 ns/op	 177.25 MB/s
+BenchmarkRandSize/4096-2       	  100000	     22523 ns/op	 181.86 MB/s
+BenchmarkRandSize/8192-2       	   30000	     43111 ns/op	 190.02 MB/s
+
+Results are similar when testing with dd, so this is not due to Go allocation
+overhead: dd if=/dev/urandom bs=16 count=100000 of=/dev/null
+*/
+func BenchmarkUrandomBlocksize(b *testing.B) {
+	for s := 16; s <= 8192; s *= 2 {
+		title := fmt.Sprintf("%d", s)
+		b.Run(title, func(b *testing.B) {
+			b.SetBytes(int64(s))
+			for i := 0; i < b.N; i++ {
+				RandBytes(s)
+			}
+		})
+	}
+}