net: introduce netdevice gso_min_segs attribute

Some TSO engines might have a too heavy setup cost, that impacts
performance on hosts sending small bursts (2 MSS per packet).

This patch adds a device gso_min_segs, allowing drivers to set
a minimum segment size for TSO packets, according to the NIC
performance.

Tested on a mlx4 NIC, this allows to get a ~110% increase of
throughput when sending 2 MSS per packet.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 9 insertions, 4 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 22d54b9b700d..2df86f50261c 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1416,6 +1416,8 @@ enum netdev_priv_flags {
  *      @gso_max_size:  Maximum size of generic segmentation offload
  *      @gso_max_segs:  Maximum number of segments that can be passed to the
  *                      NIC for GSO
+ *      @gso_min_segs:  Minimum number of segments that can be passed to the
+ *                      NIC for GSO
  *
  *      @dcbnl_ops:     Data Center Bridging netlink ops
  *      @num_tc:        Number of traffic classes in the net device
@@ -1666,7 +1668,7 @@ struct net_device {
         unsigned int            gso_max_size;
 #define GSO_MAX_SEGS            65535
         u16                     gso_max_segs;
-
+        u16                     gso_min_segs;
 #ifdef CONFIG_DCB
         const struct dcbnl_rtnl_ops *dcbnl_ops;
 #endif
diff --git a/net/core/dev.c b/net/core/dev.c
index 7d5691cc1f47..c1a4de275576 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2567,10 +2567,12 @@ static netdev_features_t harmonize_features(struct sk_buff *skb,
 
 netdev_features_t netif_skb_features(struct sk_buff *skb)
 {
+        const struct net_device *dev = skb->dev;
+        netdev_features_t features = dev->features;
+        u16 gso_segs = skb_shinfo(skb)->gso_segs;
         __be16 protocol = skb->protocol;
-        netdev_features_t features = skb->dev->features;
 
-        if (skb_shinfo(skb)->gso_segs > skb->dev->gso_max_segs)
+        if (gso_segs > dev->gso_max_segs || gso_segs < dev->gso_min_segs)
                 features &= ~NETIF_F_GSO_MASK;
 
         if (protocol == htons(ETH_P_8021Q) || protocol == htons(ETH_P_8021AD)) {
@@ -2581,7 +2583,7 @@ netdev_features_t netif_skb_features(struct sk_buff *skb)
         }
 
         features = netdev_intersect_features(features,
-                                             skb->dev->vlan_features |
+                                             dev->vlan_features |
                                              NETIF_F_HW_VLAN_CTAG_TX |
                                              NETIF_F_HW_VLAN_STAG_TX);
 
@@ -6661,6 +6663,7 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 
         dev->gso_max_size = GSO_MAX_SIZE;
         dev->gso_max_segs = GSO_MAX_SEGS;
+        dev->gso_min_segs = 0;
 
         INIT_LIST_HEAD(&dev->napi_list);
         INIT_LIST_HEAD(&dev->unreg_list);