tcp: fill shinfo->gso_size at last moment

In commit cd7d8498c9a5 ("tcp: change tcp_skb_pcount() location") we stored
gso_segs in a temporary cache hot location.

This patch does the same for gso_size.

This allows to save 2 cache line misses in tcp xmit path for
the last packet that is considered but not sent because of
various conditions (cwnd, tso defer, receiver window, TSQ...)

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

1 files changed, 8 insertions, 5 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 978cebedd3fc..950cfecaad3c 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -730,11 +730,14 @@ struct tcp_skb_cb {
                 /* Note : tcp_tw_isn is used in input path only
                  *        (isn chosen by tcp_timewait_state_process())
                  *
-                 *        tcp_gso_segs is used in write queue only,
-                 *        cf tcp_skb_pcount()
+                 *        tcp_gso_segs/size are used in write queue only,
+                 *        cf tcp_skb_pcount()/tcp_skb_mss()
                  */
                 __u32           tcp_tw_isn;
-                __u32           tcp_gso_segs;
+                struct {
+                        u16     tcp_gso_segs;
+                        u16     tcp_gso_size;
+                };
         };
         __u8            tcp_flags;      /* TCP header flags. (tcp[13])  */
 
@@ -790,10 +793,10 @@ static inline void tcp_skb_pcount_add(struct sk_buff *skb, int segs)
         TCP_SKB_CB(skb)->tcp_gso_segs += segs;
 }
 
-/* This is valid iff tcp_skb_pcount() > 1. */
+/* This is valid iff skb is in write queue and tcp_skb_pcount() > 1. */
 static inline int tcp_skb_mss(const struct sk_buff *skb)
 {
-        return skb_shinfo(skb)->gso_size;
+        return TCP_SKB_CB(skb)->tcp_gso_size;
 }
 
 /* Events passed to congestion control interface */