tcp: Apply device TSO segment limit earlier

Cache the device gso_max_segs in sock::sk_gso_max_segs and use it to
limit the size of TSO skbs.  This avoids the need to fall back to
software GSO for local TCP senders.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 9 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 3f1bcff0b10b..a7b3ec9b6c3e 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1522,21 +1522,21 @@ static void tcp_cwnd_validate(struct sock *sk)
  * when we would be allowed to send the split-due-to-Nagle skb fully.
  */
 static unsigned int tcp_mss_split_point(const struct sock *sk, const struct sk_buff *skb,
-                                        unsigned int mss_now, unsigned int cwnd)
+                                        unsigned int mss_now, unsigned int max_segs)
 {
         const struct tcp_sock *tp = tcp_sk(sk);
-        u32 needed, window, cwnd_len;
+        u32 needed, window, max_len;
 
         window = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
-        cwnd_len = mss_now * cwnd;
+        max_len = mss_now * max_segs;
 
-        if (likely(cwnd_len <= window && skb != tcp_write_queue_tail(sk)))
-                return cwnd_len;
+        if (likely(max_len <= window && skb != tcp_write_queue_tail(sk)))
+                return max_len;
 
         needed = min(skb->len, window);
 
-        if (cwnd_len <= needed)
-                return cwnd_len;
+        if (max_len <= needed)
+                return max_len;
 
         return needed - needed % mss_now;
 }
@@ -1765,7 +1765,8 @@ static bool 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 >= sk->sk_gso_max_size)
+        if (limit >= min_t(unsigned int, sk->sk_gso_max_size,
+                           sk->sk_gso_max_segs * tp->mss_cache))
                 goto send_now;
 
         /* Middle in queue won't get any more data, full sendable already? */
@@ -1999,7 +2000,9 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
                 limit = mss_now;
                 if (tso_segs > 1 && !tcp_urg_mode(tp))
                         limit = tcp_mss_split_point(sk, skb, mss_now,
-                                                    cwnd_quota);
+                                                    min_t(unsigned int,
+                                                          cwnd_quota,
+                                                          sk->sk_gso_max_segs));
 
                 if (skb->len > limit &&
                     unlikely(tso_fragment(sk, skb, limit, mss_now, gfp)))