tcp: Revert "tcp: remove header prediction"
This reverts commit 45f119bf936b1f9f546a0b139c5b56f9bb2bdc78.
Eric Dumazet says:
We found at Google a significant regression caused by
45f119bf936b1f9f546a0b139c5b56f9bb2bdc78 tcp: remove header prediction
In typical RPC (TCP_RR), when a TCP socket receives data, we now call
tcp_ack() while we used to not call it.
This touches enough cache lines to cause a slowdown.
so problem does not seem to be HP removal itself but the tcp_ack()
call. Therefore, it might be possible to remove HP after all, provided
one finds a way to elide tcp_ack for most cases.
Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/tcp.h b/include/net/tcp.h
index c546d13..9c3db05 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -634,6 +634,29 @@ static inline u32 __tcp_set_rto(const struct tcp_sock *tp)
return usecs_to_jiffies((tp->srtt_us >> 3) + tp->rttvar_us);
}
+static inline void __tcp_fast_path_on(struct tcp_sock *tp, u32 snd_wnd)
+{
+ tp->pred_flags = htonl((tp->tcp_header_len << 26) |
+ ntohl(TCP_FLAG_ACK) |
+ snd_wnd);
+}
+
+static inline void tcp_fast_path_on(struct tcp_sock *tp)
+{
+ __tcp_fast_path_on(tp, tp->snd_wnd >> tp->rx_opt.snd_wscale);
+}
+
+static inline void tcp_fast_path_check(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (RB_EMPTY_ROOT(&tp->out_of_order_queue) &&
+ tp->rcv_wnd &&
+ atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf &&
+ !tp->urg_data)
+ tcp_fast_path_on(tp);
+}
+
/* Compute the actual rto_min value */
static inline u32 tcp_rto_min(struct sock *sk)
{
