netstack/tcp: software segmentation offload

Right now, we send each tcp packet separately, we call one system
call per-packet. This patch allows to generate multiple tcp packets
and send them by sendmmsg.

The arguable part of this CL is a way how to handle multiple headers.
This CL adds the next field to the Prepandable buffer.

Nginx test results:

Server Software:        nginx/1.15.9
Server Hostname:        10.138.0.2
Server Port:            8080

Document Path:          /10m.txt
Document Length:        10485760 bytes

w/o gso:
Concurrency Level:      5
Time taken for tests:   5.491 seconds
Complete requests:      100
Failed requests:        0
Total transferred:      1048600200 bytes
HTML transferred:       1048576000 bytes
Requests per second:    18.21 [#/sec] (mean)
Time per request:       274.525 [ms] (mean)
Time per request:       54.905 [ms] (mean, across all concurrent requests)
Transfer rate:          186508.03 [Kbytes/sec] received

sw-gso:

Concurrency Level:      5
Time taken for tests:   3.852 seconds
Complete requests:      100
Failed requests:        0
Total transferred:      1048600200 bytes
HTML transferred:       1048576000 bytes
Requests per second:    25.96 [#/sec] (mean)
Time per request:       192.576 [ms] (mean)
Time per request:       38.515 [ms] (mean, across all concurrent requests)
Transfer rate:          265874.92 [Kbytes/sec] received

w/o gso:
$ ./tcp_benchmark --client --duration 15  --ideal
[SUM]  0.0-15.1 sec  2.20 GBytes  1.25 Gbits/sec

software gso:
$ tcp_benchmark --client --duration 15  --ideal --gso $((1<<16)) --swgso
[SUM]  0.0-15.1 sec  3.99 GBytes  2.26 Gbits/sec

PiperOrigin-RevId: 276112677

2 files changed, 10 insertions, 3 deletions

diff --git a/runsc/sandbox/BUILD b/runsc/sandbox/BUILD
index 7fdceaab6..27459e6d1 100644
--- a/runsc/sandbox/BUILD
+++ b/runsc/sandbox/BUILD
@@ -19,6 +19,7 @@ go_library(
         "//pkg/log",
         "//pkg/sentry/control",
         "//pkg/sentry/platform",
+        "//pkg/tcpip/stack",
         "//pkg/urpc",
         "//runsc/boot",
         "//runsc/boot/platforms",
diff --git a/runsc/sandbox/network.go b/runsc/sandbox/network.go
index 5634f0707..d42de0176 100644
--- a/runsc/sandbox/network.go
+++ b/runsc/sandbox/network.go
@@ -28,6 +28,7 @@ import (
 	"github.com/vishvananda/netlink"
 	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/log"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
 	"gvisor.dev/gvisor/pkg/urpc"
 	"gvisor.dev/gvisor/runsc/boot"
 	"gvisor.dev/gvisor/runsc/specutils"
@@ -61,7 +62,7 @@ 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, conf.GSO, conf.NumNetworkChannels); err != nil {
+		if err := createInterfacesAndRoutesFromNS(conn, nsPath, conf.HardwareGSO, conf.SoftwareGSO, conf.NumNetworkChannels); err != nil {
 			return fmt.Errorf("creating interfaces from net namespace %q: %v", nsPath, err)
 		}
 	case boot.NetworkHost:
@@ -136,7 +137,7 @@ 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, enableGSO bool, numNetworkChannels int) error {
+func createInterfacesAndRoutesFromNS(conn *urpc.Client, nsPath string, hardwareGSO bool, softwareGSO bool, numNetworkChannels int) error {
 	// Join the network namespace that we will be copying.
 	restore, err := joinNetNS(nsPath)
 	if err != nil {
@@ -232,7 +233,7 @@ func createInterfacesAndRoutesFromNS(conn *urpc.Client, nsPath string, enableGSO
 		// Create the socket for the device.
 		for i := 0; i < link.NumChannels; i++ {
 			log.Debugf("Creating Channel %d", i)
-			socketEntry, err := createSocket(iface, ifaceLink, enableGSO)
+			socketEntry, err := createSocket(iface, ifaceLink, hardwareGSO)
 			if err != nil {
 				return fmt.Errorf("failed to createSocket for %s : %v", iface.Name, err)
 			}
@@ -246,6 +247,11 @@ func createInterfacesAndRoutesFromNS(conn *urpc.Client, nsPath string, enableGSO
 			}
 			args.FilePayload.Files = append(args.FilePayload.Files, socketEntry.deviceFile)
 		}
+		if link.GSOMaxSize == 0 && softwareGSO {
+			// Hardware GSO is disabled. Let's enable software GSO.
+			link.GSOMaxSize = stack.SoftwareGSOMaxSize
+			link.SoftwareGSOEnabled = true
+		}
 
 		// Collect the addresses for the interface, enable forwarding,
 		// and remove them from the host.