switch to ASM vector checksum

overlay/checksum/checksum_test.go

@@ -0,0 +1,190 @@
+package checksum
+
+import (
+	"fmt"
+	"math/rand/v2"
+	"testing"
+
+	gvisorchecksum "gvisor.dev/gvisor/pkg/tcpip/checksum"
+)
+
+// TestChecksumMatchesGvisor walks lengths from 0 to 4096, with several initial
+// seeds and a handful of starting alignments, asserting that our local
+// Checksum matches gvisor's reference bit-for-bit.
+func TestChecksumMatchesGvisor(t *testing.T) {
+	rng := rand.New(rand.NewPCG(1, 2))
+	const padFront = 16
+
+	// Random pool large enough for the longest case + alignment slop.
+	pool := make([]byte, 4096+padFront)
+	for i := range pool {
+		pool[i] = byte(rng.Uint32())
+	}
+
+	seeds := []uint16{0, 0x0001, 0xabcd, 0xffff, 0x1234, 0xfedc}
+	offsets := []int{0, 1, 2, 3, 4, 5, 7, 8, 15, 16}
+
+	for length := 0; length <= 4096; length++ {
+		for _, seed := range seeds {
+			for _, off := range offsets {
+				if off+length > len(pool) {
+					continue
+				}
+				buf := pool[off : off+length]
+				want := gvisorchecksum.Checksum(buf, seed)
+				got := Checksum(buf, seed)
+				if got != want {
+					t.Fatalf("len=%d off=%d seed=%#x: got %#04x want %#04x",
+						length, off, seed, got, want)
+				}
+			}
+		}
+	}
+}
+
+// TestChecksumPatternedBuffers exercises specific byte patterns that have
+// historically tripped up checksum implementations: all-zero, all-0xff,
+// alternating, and ascending sequences.
+func TestChecksumPatternedBuffers(t *testing.T) {
+	for length := 0; length <= 256; length++ {
+		patterns := map[string][]byte{
+			"zeros":       make([]byte, length),
+			"ones":        bytes(length, 0xff),
+			"alternating": pattern(length, []byte{0xa5, 0x5a}),
+			"ascending":   ascending(length),
+		}
+		for name, buf := range patterns {
+			for _, seed := range []uint16{0, 0xffff, 0x8000} {
+				want := gvisorchecksum.Checksum(buf, seed)
+				got := Checksum(buf, seed)
+				if got != want {
+					t.Fatalf("%s len=%d seed=%#x: got %#04x want %#04x",
+						name, length, seed, got, want)
+				}
+			}
+		}
+	}
+}
+
+func bytes(n int, v byte) []byte {
+	b := make([]byte, n)
+	for i := range b {
+		b[i] = v
+	}
+	return b
+}
+
+func pattern(n int, p []byte) []byte {
+	b := make([]byte, n)
+	for i := range b {
+		b[i] = p[i%len(p)]
+	}
+	return b
+}
+
+func ascending(n int) []byte {
+	b := make([]byte, n)
+	for i := range b {
+		b[i] = byte(i)
+	}
+	return b
+}
+
+// TestChecksumTailPaths targets every combination of (SIMD body iterations,
+// trailing tail bytes) the asm handlers walk through. The tail handlers
+// peel off 8 → 4 → 2 → 1 byte chunks in turn; this test exercises each by
+// constructing lengths of the form 64*k + tail for tail ∈ [0, 63] and a
+// representative spread of k values, including k=0 (no main loop, all tail)
+// and k=1 (one main loop iter, then tail). It's explicit coverage for
+// payload sizes that are odd, not divisible by 4, by 8, or by 32.
+func TestChecksumTailPaths(t *testing.T) {
+	rng := rand.New(rand.NewPCG(42, 17))
+	const padFront = 16
+	const maxK = 8
+
+	pool := make([]byte, 64*maxK+padFront+64)
+	for i := range pool {
+		pool[i] = byte(rng.Uint32())
+	}
+
+	seeds := []uint16{0, 0xffff, 0xabcd}
+	offsets := []int{0, 1, 3, 7, 15} // mix of aligned and odd starts
+
+	for k := 0; k <= maxK; k++ {
+		for tail := 0; tail < 64; tail++ {
+			length := 64*k + tail
+			for _, seed := range seeds {
+				for _, off := range offsets {
+					if off+length > len(pool) {
+						continue
+					}
+					buf := pool[off : off+length]
+					want := gvisorchecksum.Checksum(buf, seed)
+					got := Checksum(buf, seed)
+					if got != want {
+						t.Fatalf("k=%d tail=%d (len=%d) off=%d seed=%#x: got %#04x want %#04x",
+							k, tail, length, off, seed, got, want)
+					}
+				}
+			}
+		}
+	}
+}
+
+// BenchmarkChecksumTailSizes covers payload sizes that aren't clean multiples
+// of the SIMD body's 32-byte (amd64) or 16-byte (arm64) chunks, so the tail
+// handler is meaningfully on the hot path. Sizes are picked to either exercise
+// every tail branch (tiny lengths) or sit slightly off realistic packet
+// boundaries (e.g. 1499 = MTU − 1).
+func BenchmarkChecksumTailSizes(b *testing.B) {
+	sizes := []int{
+		1, 3, 7, 15, 31, // sub-SIMD; entire work is scalar tail
+		33, 35, 47, 63, // one loop32 + assorted tails
+		65, 95, 127, // one loop64 + assorted tails
+		1447, 1471, 1499, 1501, // around MTU
+		8191, 8193, // around USO
+		65531, 65533, // near the kernel max
+	}
+	for _, size := range sizes {
+		buf := make([]byte, size)
+		for i := range buf {
+			buf[i] = byte(i)
+		}
+		b.Run(fmt.Sprintf("size=%d/local", size), func(b *testing.B) {
+			b.SetBytes(int64(size))
+			for i := 0; i < b.N; i++ {
+				_ = Checksum(buf, 0)
+			}
+		})
+		b.Run(fmt.Sprintf("size=%d/gvisor", size), func(b *testing.B) {
+			b.SetBytes(int64(size))
+			for i := 0; i < b.N; i++ {
+				_ = gvisorchecksum.Checksum(buf, 0)
+			}
+		})
+	}
+}
+
+// BenchmarkChecksum compares the local Checksum to gvisor's at sizes that
+// match real traffic: a TCP/IP header (60), a typical MSS (1448), a typical
+// USO size (8192), and the kernel's max GSO superpacket (65535).
+func BenchmarkChecksum(b *testing.B) {
+	for _, size := range []int{60, 1448, 8192, 65535} {
+		buf := make([]byte, size)
+		for i := range buf {
+			buf[i] = byte(i)
+		}
+		b.Run(fmt.Sprintf("size=%d/local", size), func(b *testing.B) {
+			b.SetBytes(int64(size))
+			for i := 0; i < b.N; i++ {
+				_ = Checksum(buf, 0)
+			}
+		})
+		b.Run(fmt.Sprintf("size=%d/gvisor", size), func(b *testing.B) {
+			b.SetBytes(int64(size))
+			for i := 0; i < b.N; i++ {
+				_ = gvisorchecksum.Checksum(buf, 0)
+			}
+		})
+	}
+}