tcp: GSO should be TSQ friendly
I noticed that TSQ (TCP Small queues) was less effective when TSO is
turned off, and GSO is on. If BQL is not enabled, TSQ has then no
effect.
It turns out the GSO engine frees the original gso_skb at the time the
fragments are generated and queued to the NIC.
We should instead call the tcp_wfree() destructor for the last fragment,
to keep the flow control as intended in TSQ. This effectively limits
the number of queued packets on qdisc + NIC layers.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Nandita Dukkipati <nanditad@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index a96f7b5..963bda1 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2885,6 +2885,7 @@
__be32 delta;
unsigned int oldlen;
unsigned int mss;
+ struct sk_buff *gso_skb = skb;
if (!pskb_may_pull(skb, sizeof(*th)))
goto out;
@@ -2953,6 +2954,17 @@
th->cwr = 0;
} while (skb->next);
+ /* Following permits TCP Small Queues to work well with GSO :
+ * The callback to TCP stack will be called at the time last frag
+ * is freed at TX completion, and not right now when gso_skb
+ * is freed by GSO engine
+ */
+ if (gso_skb->destructor == tcp_wfree) {
+ swap(gso_skb->sk, skb->sk);
+ swap(gso_skb->destructor, skb->destructor);
+ swap(gso_skb->truesize, skb->truesize);
+ }
+
delta = htonl(oldlen + (skb->tail - skb->transport_header) +
skb->data_len);
th->check = ~csum_fold((__force __wsum)((__force u32)th->check +