Fold the shutdown flags into one, take the smallest frame to the wire minimum, drop the speed column

loss.go

@@ -36,8 +36,8 @@ func newLossWindows(tx []*txStats) []lossWindow {
 	return w
 }
 
-// A sequence number is only judged once it falls out of the window, so frames
-// still queued in another rx worker are never miscounted as lost.
+// A sequence number is only judged once it falls out of the window, so a frame
+// that has arrived but not yet been drained is never miscounted as lost.
 //
 // Reports whether the sequence number could have come off the wire at all. One
 // above what the sender has reached is a damaged header rather than a gap, and
@@ -53,8 +53,9 @@ func (w *lossWindow) observe(seq uint64) bool {
 	}
 	w.mu.Lock()
 	if !w.inited {
-		// Start half a window below the first sequence seen, so frames another
-		// rx worker is still holding land inside the window rather than late.
+		// Start half a window below the first sequence seen, so anything the
+		// sender put on the wire before it lands inside the window rather than
+		// below the base.
 		if seq > lossSlots/2 {
 			w.base = seq - lossSlots/2
 		}

main.go

@@ -437,7 +437,7 @@ func buildDirection(label string, tx, rx endpoint) (*direction, error) {
 	return d, nil
 }
 
-func (d *direction) start(wg *sync.WaitGroup, doneTx, doneRx *atomic.Bool, rxReady *sync.WaitGroup, startTx <-chan struct{}) {
+func (d *direction) start(wg *sync.WaitGroup, done *atomic.Bool, rxReady *sync.WaitGroup, startTx <-chan struct{}) {
 	for i, fd := range d.txFDs {
 		w := &txWorker{
 			fd:      fd,
@@ -450,7 +450,7 @@ func (d *direction) start(wg *sync.WaitGroup, doneTx, doneRx *atomic.Bool, rxRea
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
-			w.run(doneTx)
+			w.run(done)
 		}()
 	}
 	for i, fd := range d.rxFDs {
@@ -466,7 +466,7 @@ func (d *direction) start(wg *sync.WaitGroup, doneTx, doneRx *atomic.Bool, rxRea
 		wg.Add(1)
 		go func() {
 			defer wg.Done()
-			w.run(doneRx)
+			w.run(done)
 		}()
 	}
 
@@ -474,20 +474,20 @@ func (d *direction) start(wg *sync.WaitGroup, doneTx, doneRx *atomic.Bool, rxRea
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
-		sender.run(doneTx, startTx)
+		sender.run(done, startTx)
 	}()
 
 	receiver := &probeReceiver{fd: d.probeRxFD, stats: d.cable, ready: rxReady}
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
-		receiver.run(doneRx)
+		receiver.run(done)
 	}()
 
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
-		d.poller.run(doneRx, startTx)
+		d.poller.run(done, startTx)
 	}()
 }
 
@@ -514,7 +514,9 @@ const (
 	linkSpeed = 10.0
 )
 
-var frameSizes = []int{64, 128, 256, 512, 1024, 1280, 1514}
+// The mac appends the fcs, so 60 and 1514 here are the smallest and largest
+// standard frames, 64 and 1518 on the wire.
+var frameSizes = []int{60, 128, 256, 512, 1024, 1280, 1514}
 
 func main() {
 	// The names the kernel gives the only two ports built into it, since as
@@ -611,19 +613,18 @@ func run(aName, bName string, nsPerM float64) error {
 	var linkRows [][]string
 	for _, e := range []endpoint{a, b} {
 		linkRows = append(linkRows, []string{
-			paint(e.tag, cCyan), e.name, e.macString(),
-			fmt.Sprintf("%.0f Gb/s", linkSpeed), fmt.Sprintf("%d", e.mtu),
+			paint(e.tag, cCyan), e.name, e.macString(), fmt.Sprintf("%d", e.mtu),
 		})
 	}
 	fmt.Println(renderBox("LINKS",
-		[]string{"TAG", "INTERFACE", "MAC", "SPEED", "MTU"},
-		[]bool{false, false, false, true, true}, linkRows))
+		[]string{"TAG", "INTERFACE", "MAC", "MTU"},
+		[]bool{false, false, false, true}, linkRows))
 	fmt.Println()
 
 	// One row carries both directions, so line rate is both links at once.
 	target := linkSpeed * float64(len(dirs))
 
-	var doneTx, doneRx atomic.Bool
+	var done atomic.Bool
 	var wg sync.WaitGroup
 	var rxReady sync.WaitGroup
 	startTx := make(chan struct{})
@@ -631,13 +632,13 @@ func run(aName, bName string, nsPerM float64) error {
 		rxReady.Add(len(d.rxFDs) + 1)
 	}
 	for _, d := range dirs {
-		d.start(&wg, &doneTx, &doneRx, &rxReady, startTx)
+		d.start(&wg, &done, &rxReady, startTx)
 	}
 	samp := &sampler{dirs: dirs}
 	wg.Add(1)
 	go func() {
 		defer wg.Done()
-		samp.run(&doneRx, startTx)
+		samp.run(&done, startTx)
 	}()
 	rxReady.Wait()
 
@@ -673,8 +674,7 @@ func run(aName, bName string, nsPerM float64) error {
 	for {
 		select {
 		case <-sig:
-			doneTx.Store(true)
-			doneRx.Store(true)
+			done.Store(true)
 			wg.Wait()
 			return nil
 		case <-space:

sock.go

@@ -15,9 +15,8 @@ type mmsghdr struct {
 
 func htons(v uint16) uint16 { return v<<8 | v>>8 }
 
-// Set through the FORCE options alone: the plain ones are clamped to wmem_max
-// and rmem_max, so falling back to them would quietly leave a fraction of this
-// and go on measuring as though it had not.
+// Set through the FORCE options alone, since the plain ones are clamped to
+// wmem_max and rmem_max and would quietly leave a fraction of this.
 const (
 	sndbufBytes = 8 << 20
 	rcvbufBytes = 64 << 20