[net-next 1/3] tipc: set default MTU for UDP media

[GhantaKrishnamurthy MohanKrishna <mohan.krishna.ghanta.krishnamurthy@ericsson.com>]

Currently, all bearers are configured with MTU value same as the
underlying L2 device. However, in case of bearers with media type
UDP, higher throughput is possible with a fixed and higher emulated
MTU value than adapting to the underlying L2 MTU.

In this commit, we introduce a parameter mtu in struct tipc_media
and a default value is set for UDP. A default value of 14k
was determined by experimentation and found to have a higher throughput
than 16k. MTU for UDP bearers are assigned the above set value of
media MTU.

Acked-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: GhantaKrishnamurthy MohanKrishna <mohan.krishna.ghanta.krishnamurthy@ericsson.com>
---
 include/uapi/linux/tipc_config.h | 5 +++++
 net/tipc/udp_media.c             | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/tipc_config.h b/include/uapi/linux/tipc_config.h
index 3f29e3c8ed06..4b2c93b1934c 100644
--- a/include/uapi/linux/tipc_config.h
+++ b/include/uapi/linux/tipc_config.h
@@ -185,6 +185,11 @@
 #define TIPC_DEF_LINK_WIN 50
 #define TIPC_MAX_LINK_WIN 8191
 
+/*
+ * Default MTU for UDP media
+ */
+
+#define TIPC_DEF_LINK_UDP_MTU 14000
 
 struct tipc_node_info {
 	__be32 addr;			/* network address of node */
diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
index e7d91f5d5cae..9783101bc4a9 100644
--- a/net/tipc/udp_media.c
+++ b/net/tipc/udp_media.c
@@ -713,8 +713,7 @@ static int tipc_udp_enable(struct net *net, struct tipc_bearer *b,
 			err = -EINVAL;
 			goto err;
 		}
-		b->mtu = dev->mtu - sizeof(struct iphdr)
-			- sizeof(struct udphdr);
+		b->mtu = b->media->mtu;
 #if IS_ENABLED(CONFIG_IPV6)
 	} else if (local.proto == htons(ETH_P_IPV6)) {
 		udp_conf.family = AF_INET6;
@@ -803,6 +802,7 @@ struct tipc_media udp_media_info = {
 	.priority	= TIPC_DEF_LINK_PRI,
 	.tolerance	= TIPC_DEF_LINK_TOL,
 	.window		= TIPC_DEF_LINK_WIN,
+	.mtu		= TIPC_DEF_LINK_UDP_MTU,
 	.type_id	= TIPC_MEDIA_TYPE_UDP,
 	.hwaddr_len	= 0,
 	.name		= "udp"
-- 
2.1.4