netstack: default recv buf auto tuning to on

This has been enabled most everywhere for a long time -- leaving it off
artificially deflates gVisor performance for users that don't know to set the
option.

Also enable it by default in tcp_benchmark.

PiperOrigin-RevId: 532532579

pkg/tcpip/transport/tcp/protocol.go

@@ -521,6 +521,7 @@ func NewProtocol(s *stack.Stack) stack.TransportProtocol {
 		},
 		congestionControl:          ccReno,
 		availableCongestionControl: []string{ccReno, ccCubic},
+		moderateReceiveBuffer:      true,
 		lingerTimeout:              DefaultTCPLingerTimeout,
 		timeWaitTimeout:            DefaultTCPTimeWaitTimeout,
 		timeWaitReuse:              tcpip.TCPTimeWaitReuseLoopbackOnly,

pkg/tcpip/transport/tcp/testing/context/context.go

@@ -220,6 +220,13 @@ func NewWithOpts(t *testing.T, opts Options) *Context {
 		t.Fatalf("s.SetTransportProtocolOption(%d, &%T(%d)): %s", tcp.ProtocolNumber, minRTOOpt, minRTOOpt, err)
 	}
 
+	// Many tests verify the window size. Autotuning can change that value,
+	// so we turn it off.
+	autoTuneOpt := tcpip.TCPModerateReceiveBufferOption(false)
+	if err := s.SetTransportProtocolOption(tcp.ProtocolNumber, &autoTuneOpt); err != nil {
+		t.Fatalf("SetTransportProtocolOption(%d, &%T(%t)): %s", tcp.ProtocolNumber, autoTuneOpt, autoTuneOpt, err)
+	}
+
 	// Some of the congestion control tests send up to 640 packets, we so
 	// set the channel size to 1000.
 	ep := channel.New(1000, opts.MTU, "")

test/benchmarks/tcp/tcp_proxy.go

@@ -59,7 +59,7 @@ var (
 	iface              = flag.String("iface", "", "network interface name to bind for netstack")
 	sack               = flag.Bool("sack", false, "enable SACK support for netstack")
 	rack               = flag.Bool("rack", false, "enable RACK in TCP")
-	moderateRecvBuf    = flag.Bool("moderate_recv_buf", false, "enable TCP Receive Buffer Auto-tuning")
+	moderateRecvBuf    = flag.Bool("moderate_recv_buf", true, "enable TCP Receive Buffer Auto-tuning")
 	cubic              = flag.Bool("cubic", false, "enable use of CUBIC congestion control for netstack")
 	gso                = flag.Int("gso", 0, "GSO maximum size")
 	swgso              = flag.Bool("swgso", false, "gVisor-level GSO")