On Thu, Jul 31, 2008 at 06:55:22PM +0800, Herbert Xu wrote:

quoted

From: Lennert Buytenhek <redacted>
Subject: [NET] use software GSO for SG+CSUM capable netdevices

If a netdevice does not support hardware GSO, allowing the stack to
use GSO anyway and then splitting the GSO skb into MSS-sized pieces
as it is handed to the netdevice for transmitting is likely still
a win at least as far as CPU usage is concerned, since it reduces
the number of trips through the output path.

This patch enables the use of GSO on any netdevice that supports SG
and hardware checksumming.  If a GSO skb is then sent to a netdevice
that supports SG and checksumming but does not support hardware GSO,
net/core/dev.c:dev_hard_start_xmit() will take care of doing the
necessary GSO segmentation in software.

Signed-off-by: Lennert Buytenhek <redacted>

Index: linux-2.6.27-rc1/include/net/sock.h
===================================================================

--- linux-2.6.27-rc1.orig/include/net/sock.h
+++ linux-2.6.27-rc1/include/net/sock.h

@@ -1085,7 +1085,12 @@ extern struct dst_entry *sk_dst_check(st
 
 static inline int sk_can_gso(const struct sock *sk)
 {
-	return net_gso_ok(sk->sk_route_caps, sk->sk_gso_type);
+	int caps = sk->sk_route_caps;
+	int type = sk->sk_gso_type;
+
+	return (caps & NETIF_F_SG) &&
+		 ((type == SKB_GSO_TCPV4 && (caps & NETIF_F_V4_CSUM)) ||
+		  (type == SKB_GSO_TCPV6 && (caps & NETIF_F_V6_CSUM)));

I think you've lost the hardware UFO support.

In any case, this is really the wrong place to do this as the
user will no longer be able to disable it.

Please do it in the netdev registration function instead.  The code
should enable NETIF_F_GSO if NETIF_F_SG is on.

Like this?




From: Lennert Buytenhek <redacted>
Subject: [NET] use software GSO for SG+CSUM capable netdevices

If a netdevice does not support hardware GSO, allowing the stack to
use GSO anyway and then splitting the GSO skb into MSS-sized pieces
as it is handed to the netdevice for transmitting is likely still
a win as far as throughput and/or CPU usage are concerned, since it
reduces the number of trips through the output path.

This patch enables the use of GSO on any netdevice that supports SG.
If a GSO skb is then sent to a netdevice that supports SG but does not
support hardware GSO, net/core/dev.c:dev_hard_start_xmit() will take
care of doing the necessary GSO segmentation in software.

Signed-off-by: Lennert Buytenhek <redacted>

Index: linux-2.6.27-rc1/net/core/dev.c
===================================================================

--- linux-2.6.27-rc1.orig/net/core/dev.c
+++ linux-2.6.27-rc1/net/core/dev.c

@@ -3988,6 +3988,10 @@ int register_netdevice(struct net_device
 		}
 	}
 
+	/* Enable software GSO if SG is supported. */
+	if (dev->features & NETIF_F_SG)
+		dev->features |= NETIF_F_GSO;
+
 	netdev_initialize_kobject(dev);
 	ret = netdev_register_kobject(dev);
 	if (ret)