Stop counting a partly filled send vector as a failure

main.go

@@ -197,7 +197,7 @@ type sample struct {
 	lost, late        uint64
 	crcErr, badMagic  uint64
 	badLen            uint64
-	txErrs, txShort   uint64
+	txErrs            uint64
 	rxErrs            uint64
 }
 
@@ -246,7 +246,6 @@ func (d *direction) snapshot() sample {
 		s.txFrames += t.frames.Load()
 		s.txBytes += t.bytes.Load()
 		s.txErrs += t.errs.Load()
-		s.txShort += t.short.Load()
 	}
 	for _, r := range d.rxStats {
 		s.rxFrames += r.frames.Load()
@@ -331,16 +330,14 @@ func errsBetween(b, n counterSet) errs {
 		// checksum, a header that is not ours, and a length that cannot be.
 		corrupt: (n.s.crcErr - b.s.crcErr) + (n.s.badMagic - b.s.badMagic) +
 			(n.s.badLen - b.s.badLen),
-		// A frame the stack refused and a frame the driver dropped are the same
-		// failure seen from either side of the ring, and never the same frame
-		// twice: a send that fails never reaches the driver to be dropped.
-		link: (n.nic - b.nic) + (n.s.txErrs - b.s.txErrs) + (n.s.rxErrs - b.s.rxErrs),
-		// Ours rather than the cable's: frames the kernel threw away because we
-		// did not drain the ring fast enough, and frames so far out of order
-		// that our own bookkeeping had already written them off. The second is
-		// unreachable while each stream has a flow rule to its own queue, which
-		// is exactly why it is worth counting: it fires if that stops holding.
-		internal: (n.drops - b.drops) + (n.s.late - b.s.late),
+		// What the hardware reported. Nothing the host declined to send is here,
+		// so this one going red means the cable.
+		link: (n.nic - b.nic) + (n.s.rxErrs - b.s.rxErrs),
+		// Ours rather than the cable's. A late frame is unreachable while each
+		// stream has a flow rule to its own queue, which is exactly why it is
+		// worth counting.
+		internal: (n.drops - b.drops) + (n.s.late - b.s.late) +
+			(n.s.txErrs - b.s.txErrs),
 	}
 }
 

tx.go

@@ -10,8 +10,7 @@ type txStats struct {
 	frames atomic.Uint64
 	bytes  atomic.Uint64
 	errs   atomic.Uint64
-	short  atomic.Uint64
-	_      [32]byte
+	_      [40]byte
 }
 
 type txWorker struct {
@@ -62,13 +61,10 @@ func (w *txWorker) run(done *atomic.Bool) {
 			w.stats.bytes.Add(b)
 			seq += uint64(n)
 		}
-		if n < w.batch {
-			switch {
-			case n < 0 && err != unix.EINTR && err != unix.EAGAIN && err != unix.ENOBUFS:
+		// Taking fewer of the vector than offered is the ring's room, not a frame
+		// lost: the rest go on the next pass.
+		if n < 0 && err != unix.EINTR && err != unix.EAGAIN && err != unix.ENOBUFS {
 			w.stats.errs.Add(1)
-			default:
-				w.stats.short.Add(1)
-			}
 		}
 	}
 }