tcp: remove prequeue support

prequeue is a tcp receive optimization that moves part of rx processing
from bh to process context.

This only works if the socket being processed belongs to a process that
is blocked in recv on that socket.

In practice, this doesn't happen anymore that often because nowadays
servers tend to use an event driven (epoll) model.

Even normal client applications (web browsers) commonly use many tcp
connections in parallel.

This has measureable impact only in netperf (which uses plain recv and
thus allows prequeue use) from host to locally running vm (~4%), however,
there were no changes when using netperf between two physical hosts with
ixgbe interfaces.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 0 insertions, 12 deletions

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index c0feeeef962a..f753f9d2fee3 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -239,7 +239,6 @@ static int tcp_write_timeout(struct sock *sk)
 /* Called with BH disabled */
 void tcp_delack_timer_handler(struct sock *sk)
 {
-        struct tcp_sock *tp = tcp_sk(sk);
         struct inet_connection_sock *icsk = inet_csk(sk);
 
         sk_mem_reclaim_partial(sk);
@@ -254,17 +253,6 @@ void tcp_delack_timer_handler(struct sock *sk)
         }
         icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
 
-        if (!skb_queue_empty(&tp->ucopy.prequeue)) {
-                struct sk_buff *skb;
-
-                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSCHEDULERFAILED);
-
-                while ((skb = __skb_dequeue(&tp->ucopy.prequeue)) != NULL)
-                        sk_backlog_rcv(sk, skb);
-
-                tp->ucopy.memory = 0;
-        }
-
         if (inet_csk_ack_scheduled(sk)) {
                 if (!icsk->icsk_ack.pingpong) {
                         /* Delayed ACK missed: inflate ATO. */