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

From: PJ Waskiewicz <[email-masked]>
Date: Tue, 12 Feb 2008 14:01:32 -0800

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 047d432..ed1cc32 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -616,6 +616,7 @@ struct net_device
 
 	/* Partially transmitted GSO packet. */
 	struct sk_buff		*gso_skb;
+	int			max_gso_frame_size;
 
 	/* ingress path synchronizer */
 	spinlock_t		ingress_lock;
@@ -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, int 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..1977c05 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;
+	int			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 9549417..f635b29 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4022,6 +4022,7 @@ 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 433715f..a8b0ae5 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) {