Subject: [PATCH] [NET 2.6.26]: Add per-connection option to set max TSO frame size

From: PJ Waskiewicz <[email-masked]>
Date: Wed, 27 Feb 2008 09:26:06 -0800

Update: Respun for net-2.6.26 tree.

Update: changed max_gso_frame_size and sk_gso_max_size from signed to
unsigned - thanks Stephen!

This patch adds the ability for device drivers to control the size of the
TSO frames being sent to them, per TCP connection.  By setting the
netdevice's max_gso_frame_size value, the socket layer will set the GSO
frame size based on that value.  This will propogate into the TCP layer,
and send TSO's of that size to the hardware.

This can be desirable to help tune the bursty nature of TSO on a
per-adapter basis, where one may have 1 GbE and 10 GbE devices coexisting
in a system, one running multiqueue and the other not, etc.

This can also be desirable for devices that cannot support full 64 KB
TSO's, but still want to benefit from some level of segmentation
offloading.

Signed-off-by: Peter P Waskiewicz Jr <[email-masked]>
---

 include/linux/netdevice.h |    6 ++++++
 include/net/sock.h        |    2 ++
 net/core/dev.c            |    1 +
 net/core/sock.c           |    6 ++++--
 net/ipv4/tcp_output.c     |    4 ++--
 5 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index a2f0032..3bf825b 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -620,6 +620,7 @@ struct net_device
 
 	/* Partially transmitted GSO packet. */
 	struct sk_buff		*gso_skb;
+	u16			max_gso_frame_size;
 
 /*
  * One part is mostly used on xmit path (device)
@@ -1475,6 +1476,11 @@ static inline int netif_needs_gso(struct net_device *dev, struct sk_buff *skb)
 		unlikely(skb->ip_summed != CHECKSUM_PARTIAL));
 }
 
+static inline void netif_set_max_gso_size(struct net_device *dev, u16 size)
+{
+       dev->max_gso_frame_size = size;
+}
+
 /* On bonding slaves other than the currently active slave, suppress
  * duplicates except for 802.3ad ETH_P_SLOW, alb non-mcast/bcast, and
  * ARP on active-backup slaves with arp_validate enabled.
diff --git a/include/net/sock.h b/include/net/sock.h
index 8a7889b..2b07af0 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -151,6 +151,7 @@ struct sock_common {
   *	@sk_no_check: %SO_NO_CHECK setting, wether or not checkup packets
   *	@sk_route_caps: route capabilities (e.g. %NETIF_F_TSO)
   *	@sk_gso_type: GSO type (e.g. %SKB_GSO_TCPV4)
+  *	@sk_gso_max_size: Maximum GSO segment size to build
   *	@sk_lingertime: %SO_LINGER l_linger setting
   *	@sk_backlog: always used with the per-socket spinlock held
   *	@sk_callback_lock: used with the callbacks in the end of this struct
@@ -236,6 +237,7 @@ struct sock {
 	gfp_t			sk_allocation;
 	int			sk_route_caps;
 	int			sk_gso_type;
+	__u16			sk_gso_max_size;
 	int			sk_rcvlowat;
 	unsigned long 		sk_flags;
 	unsigned long	        sk_lingertime;
diff --git a/net/core/dev.c b/net/core/dev.c
index 908f07c..689a678 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4021,6 +4021,7 @@ struct net_device *alloc_netdev_mq(int sizeof_priv, const char *name,
 	}
 
 	dev->egress_subqueue_count = queue_count;
+	dev->max_gso_frame_size = 65536;
 
 	dev->get_stats = internal_stats;
 	netpoll_netdev_init(dev);
diff --git a/net/core/sock.c b/net/core/sock.c
index 09cb3a7..49dacd5 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1076,10 +1076,12 @@ void sk_setup_caps(struct sock *sk, struct dst_entry *dst)
 	if (sk->sk_route_caps & NETIF_F_GSO)
 		sk->sk_route_caps |= NETIF_F_GSO_SOFTWARE;
 	if (sk_can_gso(sk)) {
-		if (dst->header_len)
+		if (dst->header_len) {
 			sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
-		else
+		} else {
 			sk->sk_route_caps |= NETIF_F_SG | NETIF_F_HW_CSUM;
+			sk->sk_gso_max_size = dst->dev->max_gso_frame_size;
+		}
 	}
 }
 EXPORT_SYMBOL_GPL(sk_setup_caps);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ed750f9..8cd128d 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -998,7 +998,7 @@ unsigned int tcp_current_mss(struct sock *sk, int large_allowed)
 	xmit_size_goal = mss_now;
 
 	if (doing_tso) {
-		xmit_size_goal = (65535 -
+		xmit_size_goal = ((sk->sk_gso_max_size - 1) -
 				  inet_csk(sk)->icsk_af_ops->net_header_len -
 				  inet_csk(sk)->icsk_ext_hdr_len -
 				  tp->tcp_header_len);
@@ -1274,7 +1274,7 @@ static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
 	limit = min(send_win, cong_win);
 
 	/* If a full-sized TSO skb can be sent, do it. */
-	if (limit >= 65536)
+	if (limit >= sk->sk_gso_max_size)
 		goto send_now;
 
 	if (sysctl_tcp_tso_win_divisor) {