Drive a noise cable on the i40e pair, cycling its link down and up since the module PHYs ignore everything softer, and flag its absence beside the error columns

main.go

@@ -252,6 +252,7 @@ var intervalCols = []colSpec{
 	{group: "NOW", title: "corrupt", width: 7, right: true},
 	{group: "NOW", title: "link", width: 7, right: true},
 	{group: "NOW", title: "internal", width: 8, right: true},
+	{group: "NOW", title: "noise", width: 7, right: true},
 	{group: "OVERALL", title: "elapsed", width: 9, right: true},
 	{group: "OVERALL", title: "packets", width: 9, right: true},
 	{group: "OVERALL", title: "bytes", width: 9, right: true},
@@ -340,9 +341,10 @@ func (d *direction) displayView() view {
 	return v
 }
 
-// The same figures the panel draws, in the same order: the last second as rates
-// and error flags, then everything since the reset.
-func totalRow(elapsed time.Duration, v view, target float64, length string) []string {
+// The same figures the panel draws, in the same order: the last second as
+// rates and error flags with the noise cable riding at the end of them, then
+// everything since the reset.
+func totalRow(elapsed time.Duration, v view, target float64, length string, noiseMissing uint64) []string {
 	return []string{
 		rateCell(v.rxGbps*1e9, target*1e9),
 		scaleSI(v.rxPPS),
@@ -350,6 +352,7 @@ func totalRow(elapsed time.Duration, v view, target float64, length string) []st
 		flagCell(v.window.corrupt),
 		flagCell(v.window.link),
 		flagCell(v.window.internal),
+		flagCell(noiseMissing),
 		scaleTime(elapsed),
 		scaleCount(v.rxFrames),
 		scaleCount(v.rxBytes),
@@ -513,6 +516,8 @@ const (
 
 	probeEther uint16 = etherBase + numStreams
 
+	testDriver = "ice"
+
 	// A constant rather than the negotiated speed, since this has to come up
 	// with no cable in the port and nothing to negotiate.
 	linkSpeed = 10.0
@@ -523,10 +528,11 @@ const (
 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
-	// 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")
+	// Left empty, the test pair is found by driver name instead: as PID 1 there
+	// is no udev to pin names and no command line to pass, and which port gets
+	// which ethN shifts with every driver built into the kernel.
+	aName := flag.String("a", "", "first interface (default: the ice pair)")
+	bName := flag.String("b", "", "second interface")
 	nsPerM := flag.Float64("ns-per-m", 4.85, "mean of both directions, per metre of cable")
 	flag.Parse()
 
@@ -580,6 +586,13 @@ func run(aName, bName string, nsPerM float64) error {
 		return err
 	}
 
+	if aName == "" || bName == "" {
+		var err error
+		aName, bName, err = driverPair(testDriver)
+		if err != nil {
+			return err
+		}
+	}
 	a, err := lookupEndpoint(aName)
 	if err != nil {
 		return err
@@ -588,6 +601,11 @@ func run(aName, bName string, nsPerM float64) error {
 	if err != nil {
 		return err
 	}
+	noise, err := newNoiser()
+	if err != nil {
+		return err
+	}
+	defer noise.close()
 	for _, e := range []endpoint{a, b} {
 		for _, s := range frameSizes {
 			if s > e.mtu+ethHdrLen {
@@ -596,7 +614,8 @@ func run(aName, bName string, nsPerM float64) error {
 		}
 	}
 
-	a.tag, b.tag = "A", "B"
+	a.tag, b.tag = "TEST A", "TEST B"
+	noise.eps[0].tag, noise.eps[1].tag = "NOISE A", "NOISE B"
 	ifnames := []string{a.name, b.name}
 
 	ethertypes := make([]uint16, numStreams)
@@ -604,7 +623,8 @@ func run(aName, bName string, nsPerM float64) error {
 		ethertypes[i] = uint16(etherBase + i)
 	}
 
-	if err := reportChecks("HOST SETTINGS", configureSystem(ifnames, ethertypes)); err != nil {
+	if err := reportChecks("HOST SETTINGS",
+		append(configureSystem(ifnames, ethertypes), configureNoise(noise.names())...)); err != nil {
 		return err
 	}
 
@@ -623,7 +643,7 @@ func run(aName, bName string, nsPerM float64) error {
 	}()
 
 	var linkRows [][]string
-	for _, e := range []endpoint{a, b} {
+	for _, e := range []endpoint{a, b, noise.eps[0], noise.eps[1]} {
 		linkRows = append(linkRows, []string{
 			paint(e.tag, cCyan), e.name, e.macString(), fmt.Sprintf("%d", e.mtu),
 		})
@@ -652,6 +672,13 @@ func run(aName, bName string, nsPerM float64) error {
 		defer wg.Done()
 		samp.run(&done, startTx)
 	}()
+	// Not gated on startTx: the cycle and the connected verdict are wanted the
+	// moment the panel is, and nothing it does touches the measurement.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		noise.run(&done)
+	}()
 	// Every return from here on stops the workers before the deferred closes
 	// pull their sockets out from under them: otherwise the sampler panics on a
 	// closed fd and can mask the error that actually ended the run. An error
@@ -719,7 +746,8 @@ func run(aName, bName string, nsPerM float64) error {
 			if m, ok := cableMetres(views, nsPerM); ok {
 				cable = fmt.Sprintf("%.1f", m)
 			}
-			if err := disp.render(totalView(views), now.Sub(start), cable); err != nil {
+			if err := disp.render(totalView(views), now.Sub(start), cable,
+				noise.missing()); err != nil {
 				return err
 			}
 		case now := <-tick.C:
@@ -733,7 +761,8 @@ func run(aName, bName string, nsPerM float64) error {
 			if m, ok := cableMetres(rows, nsPerM); ok {
 				length = fmt.Sprintf("%.1f", m)
 			}
-			for _, line := range stats.emit(totalRow(elapsed, totalView(rows), target, length)) {
+			for _, line := range stats.emit(totalRow(elapsed, totalView(rows), target, length,
+				noise.missing())) {
 				fmt.Println(line)
 			}
 		}