gvisor/runsc: enable generic segmentation offload (GSO)

The linux packet socket can handle GSO packets, so we can segment packets to
64K instead of the MTU which is usually 1500.

Here are numbers for the nginx-1m test:
runsc:		579330.01 [Kbytes/sec] received
runsc-gso:	1794121.66 [Kbytes/sec] received
runc:		2122139.06 [Kbytes/sec] received

and for tcp_benchmark:

$ tcp_benchmark  --duration 15   --ideal
[  4]  0.0-15.0 sec  86647 MBytes  48456 Mbits/sec

$ tcp_benchmark --client --duration 15   --ideal
[  4]  0.0-15.0 sec  2173 MBytes  1214 Mbits/sec

$ tcp_benchmark --client --duration 15   --ideal --gso 65536
[  4]  0.0-15.0 sec  19357 MBytes  10825 Mbits/sec

PiperOrigin-RevId: 241072403
Change-Id: I20b03063a1a6649362b43609cbbc9b59be06e6d5

1 files changed, 16 insertions, 2 deletions

diff --git a/runsc/sandbox/network.go b/runsc/sandbox/network.go
index ec0a252d1..be924ae25 100644
--- a/runsc/sandbox/network.go
+++ b/runsc/sandbox/network.go
@@ -26,6 +26,7 @@ import (
 
 	specs "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/vishvananda/netlink"
+	"golang.org/x/sys/unix"
 	"gvisor.googlesource.com/gvisor/pkg/log"
 	"gvisor.googlesource.com/gvisor/pkg/urpc"
 	"gvisor.googlesource.com/gvisor/runsc/boot"
@@ -67,7 +68,7 @@ func setupNetwork(conn *urpc.Client, pid int, spec *specs.Spec, conf *boot.Confi
 		// Build the path to the net namespace of the sandbox process.
 		// This is what we will copy.
 		nsPath := filepath.Join("/proc", strconv.Itoa(pid), "ns/net")
-		if err := createInterfacesAndRoutesFromNS(conn, nsPath); err != nil {
+		if err := createInterfacesAndRoutesFromNS(conn, nsPath, conf.GSO); err != nil {
 			return fmt.Errorf("creating interfaces from net namespace %q: %v", nsPath, err)
 		}
 	case boot.NetworkHost:
@@ -137,7 +138,7 @@ func isRootNS() (bool, error) {
 // createInterfacesAndRoutesFromNS scrapes the interface and routes from the
 // net namespace with the given path, creates them in the sandbox, and removes
 // them from the host.
-func createInterfacesAndRoutesFromNS(conn *urpc.Client, nsPath string) error {
+func createInterfacesAndRoutesFromNS(conn *urpc.Client, nsPath string, enableGSO bool) error {
 	// Join the network namespace that we will be copying.
 	restore, err := joinNetNS(nsPath)
 	if err != nil {
@@ -246,6 +247,19 @@ func createInterfacesAndRoutesFromNS(conn *urpc.Client, nsPath string) error {
 			return fmt.Errorf("getting link for interface %q: %v", iface.Name, err)
 		}
 
+		if enableGSO {
+			gso, err := isGSOEnabled(fd, iface.Name)
+			if err != nil {
+				return fmt.Errorf("getting GSO for interface %q: %v", iface.Name, err)
+			}
+			if gso {
+				if err := syscall.SetsockoptInt(fd, syscall.SOL_PACKET, unix.PACKET_VNET_HDR, 1); err != nil {
+					return fmt.Errorf("unable to enable the PACKET_VNET_HDR option: %v", err)
+				}
+				link.GSOMaxSize = ifaceLink.Attrs().GSOMaxSize
+			}
+		}
+
 		// Collect the addresses for the interface, enable forwarding,
 		// and remove them from the host.
 		for _, addr := range ip4addrs {