Hardcode the settled sizes, streams and batch instead of carrying flags for them

main.go

@@ -7,7 +7,6 @@ import (
 	"os"
 	"os/signal"
 	"slices"
-	"strconv"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -221,28 +220,6 @@ func lookupEndpoint(name string) (endpoint, error) {
 		speed: float64(v) / 1000}, nil
 }
 
-func parseSizes(s string) ([]int, error) {
-	var out []int
-	for _, f := range strings.Split(s, ",") {
-		f = strings.TrimSpace(f)
-		if f == "" {
-			continue
-		}
-		v, err := strconv.Atoi(f)
-		if err != nil {
-			return nil, fmt.Errorf("bad size %q: %w", f, err)
-		}
-		if v < minFrame {
-			return nil, fmt.Errorf("size %d below minimum %d", v, minFrame)
-		}
-		out = append(out, v)
-	}
-	if len(out) == 0 {
-		return nil, fmt.Errorf("no sizes given")
-	}
-	return out, nil
-}
-
 func (d *direction) snapshot() sample {
 	var s sample
 	for _, t := range d.txStats {
@@ -447,10 +424,10 @@ func (d *direction) primeCounters() {
 	d.prevConsole = d.base
 }
 
-func buildDirection(label string, tx, rx endpoint, sizes []int, cfg config) (*direction, error) {
+func buildDirection(label string, tx, rx endpoint) (*direction, error) {
 	d := &direction{
 		short:   tx.tag + "→" + rx.tag,
-		streams: newLossWindows(cfg.streams),
+		streams: newLossWindows(numStreams),
 		cable:   newCableStats(),
 	}
 	// Held open for the life of the run: the stats ioctl is issued five times a
@@ -467,9 +444,9 @@ func buildDirection(label string, tx, rx endpoint, sizes []int, cfg config) (*di
 	}
 	d.win = newRateWindow(int(rateWindowSpan/sampleInterval) + 1)
 
-	for i := 0; i < cfg.streams; i++ {
+	for i := 0; i < numStreams; i++ {
 		et := uint16(etherBase + i)
-		d.specs = append(d.specs, newFrameSpec(rx.mac, tx.mac, et, sizes))
+		d.specs = append(d.specs, newFrameSpec(rx.mac, tx.mac, et, frameSizes))
 
 		fd, err := openTxSocket(tx.idx)
 		if err != nil {
@@ -488,7 +465,7 @@ func buildDirection(label string, tx, rx endpoint, sizes []int, cfg config) (*di
 
 	// Deliberately given no flow rule: a few frames a second does not need a
 	// queue of its own, and the stamps are taken at the wire either way.
-	d.probeSpec = newFrameSpec(rx.mac, tx.mac, cfg.probeEther, []int{probeSize})
+	d.probeSpec = newFrameSpec(rx.mac, tx.mac, probeEther, []int{probeSize})
 	fd, err := openTxSocket(tx.idx)
 	if err != nil {
 		return nil, fmt.Errorf("%s probe tx socket: %w", label, err)
@@ -497,7 +474,7 @@ func buildDirection(label string, tx, rx endpoint, sizes []int, cfg config) (*di
 		return nil, fmt.Errorf("%s probe tx timestamps: %w", label, err)
 	}
 	d.probeTxFD = fd
-	fd, err = openRxSocket(rx.idx, cfg.probeEther)
+	fd, err = openRxSocket(rx.idx, probeEther)
 	if err != nil {
 		return nil, fmt.Errorf("%s probe rx socket: %w", label, err)
 	}
@@ -509,13 +486,13 @@ func buildDirection(label string, tx, rx endpoint, sizes []int, cfg config) (*di
 	return d, nil
 }
 
-func (d *direction) start(wg *sync.WaitGroup, doneTx, doneRx *atomic.Bool, cfg config, rxReady *sync.WaitGroup, startTx <-chan struct{}) {
+func (d *direction) start(wg *sync.WaitGroup, doneTx, doneRx *atomic.Bool, rxReady *sync.WaitGroup, startTx <-chan struct{}) {
 	for i, fd := range d.txFDs {
 		w := &txWorker{
 			fd:      fd,
 			stream:  uint16(i),
 			spec:    d.specs[i],
-			batch:   cfg.batch,
+			batch:   batchSize,
 			stats:   d.txStats[i],
 			startTx: startTx,
 		}
@@ -528,7 +505,7 @@ func (d *direction) start(wg *sync.WaitGroup, doneTx, doneRx *atomic.Bool, cfg c
 	for i, fd := range d.rxFDs {
 		w := &rxWorker{
 			fd:      fd,
-			batch:   cfg.batch,
+			batch:   batchSize,
 			spec:    d.specs[i],
 			stats:   d.rxStats[i],
 			streams: d.streams,
@@ -574,31 +551,26 @@ func (d *direction) close() {
 	unix.Close(d.statFD)
 }
 
-type config struct {
-	streams    int
-	batch      int
-	probeEther uint16
-	nsPerM     float64
-}
+const (
+	numStreams = 7
+	batchSize  = 64
+
+	probeEther uint16 = etherBase + numStreams
+)
+
+var frameSizes = []int{64, 128, 256, 512, 1024, 1280, 1514}
 
 func main() {
-	var (
 	// The names the kernel gives the only two ports built into it, since as
 	// PID 1 there is no udev to rename them and no command line to pass.
-		aName    = flag.String("a", "eth0", "first interface")
-		bName    = flag.String("b", "eth1", "second interface")
-		sizesArg = flag.String("sizes", "64,128,256,512,1024,1280,1514", "frame sizes in bytes, excluding FCS, cycled per packet")
-		streams  = flag.Int("streams", 7, "independent streams per direction, capped by rx rings; each gets its own ethertype, steered by a flow rule to its own rx queue")
-		batch    = flag.Int("batch", 64, "frames per sendmmsg/recvmmsg call")
-
-		nsPerM = flag.Float64("ns-per-m", 4.85, "mean of both directions, per metre of cable")
-	)
+	aName := flag.String("a", "eth0", "first interface")
+	bName := flag.String("b", "eth1", "second interface")
+	nsPerM := flag.Float64("ns-per-m", 4.85, "mean of both directions, per metre of cable")
 	flag.Parse()
 
 	// Nothing here is recoverable by the time it reaches this point, and as PID 1
 	// a plain exit would panic the kernel anyway with less to show for it.
-	if err := run(*aName, *bName, *sizesArg,
-		*streams, *batch, *nsPerM); err != nil {
+	if err := run(*aName, *bName, *nsPerM); err != nil {
 		panic(err)
 	}
 }
@@ -634,14 +606,7 @@ func (s *sampler) run(done *atomic.Bool, startTx <-chan struct{}) {
 	}
 }
 
-func run(aName, bName, sizesArg string,
-	nStreams, batch int, nsPerM float64) error {
-
-	sizes, err := parseSizes(sizesArg)
-	if err != nil {
-		return err
-	}
-
+func run(aName, bName string, nsPerM float64) error {
 	if err := reportChecks("BOOT", bootstrap()); err != nil {
 		return err
 	}
@@ -655,7 +620,7 @@ func run(aName, bName, sizesArg string,
 		return err
 	}
 	for _, e := range []endpoint{a, b} {
-		for _, s := range sizes {
+		for _, s := range frameSizes {
 			if s > e.mtu+ethHdrLen {
 				return fmt.Errorf("size %d exceeds %s MTU %d (max frame %d)", s, e.name, e.mtu, e.mtu+ethHdrLen)
 			}
@@ -665,10 +630,7 @@ func run(aName, bName, sizesArg string,
 	a.tag, b.tag = "A", "B"
 	ifnames := []string{a.name, b.name}
 
-	if nStreams < 1 {
-		return fmt.Errorf("need at least one stream")
-	}
-	ethertypes := make([]uint16, nStreams)
+	ethertypes := make([]uint16, numStreams)
 	for i := range ethertypes {
 		ethertypes[i] = uint16(etherBase + i)
 	}
@@ -677,16 +639,9 @@ func run(aName, bName, sizesArg string,
 		return err
 	}
 
-	cfg := config{
-		streams:    nStreams,
-		batch:      batch,
-		probeEther: uint16(etherBase + nStreams),
-		nsPerM:     nsPerM,
-	}
-
 	var dirs []*direction
 	for _, p := range [][2]endpoint{{a, b}, {b, a}} {
-		d, err := buildDirection(p[0].name+"->"+p[1].name, p[0], p[1], sizes, cfg)
+		d, err := buildDirection(p[0].name+"->"+p[1].name, p[0], p[1])
 		if err != nil {
 			return err
 		}
@@ -710,8 +665,8 @@ func run(aName, bName, sizesArg string,
 		[]bool{false, false, false, true, true}, linkRows))
 
 	target := a.speed
-	sizeStrs := make([]string, len(sizes))
-	for i, s := range sizes {
+	sizeStrs := make([]string, len(frameSizes))
+	for i, s := range frameSizes {
 		sizeStrs[i] = fmt.Sprintf("%d", s)
 	}
 	fmt.Println(renderBox("CONFIG",
@@ -719,9 +674,9 @@ func run(aName, bName, sizesArg string,
 		[]bool{false, false}, [][]string{
 			{"frame sizes", strings.Join(sizeStrs, " ")},
 			{"streams", fmt.Sprintf("%d per direction, ethertypes 0x%04x-0x%04x",
-				nStreams, ethertypes[0], ethertypes[len(ethertypes)-1])},
-			{"probe", fmt.Sprintf("ethertype 0x%04x every %s", cfg.probeEther, probeInterval)},
-			{"batch", fmt.Sprintf("%d frames per syscall", batch)},
+				numStreams, ethertypes[0], ethertypes[len(ethertypes)-1])},
+			{"probe", fmt.Sprintf("ethertype 0x%04x every %s", probeEther, probeInterval)},
+			{"batch", fmt.Sprintf("%d frames per syscall", batchSize)},
 			{"calibration", fmt.Sprintf("%g ns/m, zero taken from the shortest delay seen so far", nsPerM)},
 			{"buffers", fmt.Sprintf("sndbuf %s, rcvbuf %s",
 				humanBytes(uint64(sockBufSize(dirs[0].txFDs[0], unix.SO_SNDBUF))),
@@ -737,7 +692,7 @@ func run(aName, bName, sizesArg string,
 		rxReady.Add(len(d.rxFDs) + 1)
 	}
 	for _, d := range dirs {
-		d.start(&wg, &doneTx, &doneRx, cfg, &rxReady, startTx)
+		d.start(&wg, &doneTx, &doneRx, &rxReady, startTx)
 	}
 	samp := &sampler{dirs: dirs}
 	wg.Add(1)
@@ -798,7 +753,7 @@ func run(aName, bName, sizesArg string,
 			// Empty until the probe has a stamp from each direction, so the
 			// panel shows nothing there rather than a placeholder.
 			cable := ""
-			if m, ok := cfg.cableMetres(views); ok {
+			if m, ok := cableMetres(views, nsPerM); ok {
 				cable = fmt.Sprintf("%.1f", m)
 			}
 			if err := disp.render(totalView(views), now.Sub(start), cable); err != nil {
@@ -812,7 +767,7 @@ func run(aName, bName, sizesArg string,
 				rows[i] = d.view(now)
 			}
 			length := "-"
-			if m, ok := cfg.cableMetres(rows); ok {
+			if m, ok := cableMetres(rows, nsPerM); ok {
 				length = fmt.Sprintf("%.1f", m)
 			}
 			for i, d := range dirs {

probe.go

@@ -54,7 +54,7 @@ func (v cableView) minText() string {
 
 // Averaging the two directions cancels the phy asymmetry between them, which is
 // about 790ns and swamps any cable, so one direction alone cannot give a length.
-func (c config) cableMetres(views []view) (float64, bool) {
+func cableMetres(views []view, nsPerM float64) (float64, bool) {
 	if len(views) == 0 {
 		return 0, false
 	}
@@ -65,7 +65,7 @@ func (c config) cableMetres(views []view) (float64, bool) {
 		}
 		excess += float64(v.cable.min - v.cable.floor)
 	}
-	return excess / float64(len(views)) / c.nsPerM, true
+	return excess / float64(len(views)) / nsPerM, true
 }
 
 func newCableStats() *cableStats {