tcp: call tcp_set_skb_tso_segs() from tcp_write_xmit()

tcp_write_xmit() calls tcp_init_tso_segs()
to set gso_size and gso_segs on the packet.

tcp_init_tso_segs() requires the stack to maintain
an up to date tcp_skb_pcount(), and this makes sense
for packets in rtx queue. Not so much for packets
still in the write queue.

In the following patch, we don't want to deal with
tcp_skb_pcount() when moving payload from 2nd
skb to 1st skb in the write queue.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240418214600.1291486-3-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index acbc76ca3e640354880c62c2423cfe4ba99f0be3..5e8665241f9345f38ce56afffe473948aef66786 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1502,18 +1502,22 @@ static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
 }
 
 /* Initialize TSO segments for a packet. */
-static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
+static int tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
 {
+       int tso_segs;
+
        if (skb->len <= mss_now) {
                /* Avoid the costly divide in the normal
                 * non-TSO case.
                 */
-               tcp_skb_pcount_set(skb, 1);
                TCP_SKB_CB(skb)->tcp_gso_size = 0;
-       } else {
-               tcp_skb_pcount_set(skb, DIV_ROUND_UP(skb->len, mss_now));
-               TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
+               tcp_skb_pcount_set(skb, 1);
+               return 1;
        }
+       TCP_SKB_CB(skb)->tcp_gso_size = mss_now;
+       tso_segs = DIV_ROUND_UP(skb->len, mss_now);
+       tcp_skb_pcount_set(skb, tso_segs);
+       return tso_segs;
 }
 
 /* Pcount in the middle of the write queue got changed, we need to do various
@@ -2097,10 +2101,9 @@ static int tcp_init_tso_segs(struct sk_buff *skb, unsigned int mss_now)
 {
        int tso_segs = tcp_skb_pcount(skb);
 
-       if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now)) {
-               tcp_set_skb_tso_segs(skb, mss_now);
-               tso_segs = tcp_skb_pcount(skb);
-       }
+       if (!tso_segs || (tso_segs > 1 && tcp_skb_mss(skb) != mss_now))
+               return tcp_set_skb_tso_segs(skb, mss_now);
+
        return tso_segs;
 }
 
@@ -2733,9 +2736,6 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
                if (tcp_pacing_check(sk))
                        break;
 
-               tso_segs = tcp_init_tso_segs(skb, mss_now);
-               BUG_ON(!tso_segs);
-
                cwnd_quota = tcp_cwnd_test(tp);
                if (!cwnd_quota) {
                        if (push_one == 2)
@@ -2745,6 +2745,8 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
                                break;
                }
 
+               tso_segs = tcp_set_skb_tso_segs(skb, mss_now);
+
                if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) {
                        is_rwnd_limited = true;
                        break;