netdev - Re: [PATCH net-next] tcp: always send a quick ack when quickacks are enabled

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Message-ID: <1436252703.4571.20.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 07 Jul 2015 09:05:03 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jon Maxwell <jmaxwell37@...il.com>
Cc:	davem@...emloft.net, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jmaxwell@...hat.com
Subject: Re: [PATCH net-next] tcp: always send a quick ack when quickacks
 are enabled

On Tue, 2015-07-07 at 14:22 +1000, Jon Maxwell wrote:


> @@ -4887,6 +4884,7 @@ static inline void tcp_data_snd_check(struct sock *sk)
>  static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
>  {
>  	struct tcp_sock *tp = tcp_sk(sk);
> +	const struct dst_entry *dst = __sk_dst_get(sk);
>  
>  	    /* More than one full frame received... */
>  	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
> @@ -4896,6 +4894,8 @@ static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
>  	     __tcp_select_window(sk) >= tp->rcv_wnd) ||
>  	    /* We ACK each frame or... */
>  	    tcp_in_quickack_mode(sk) ||
> +	    /* quickack on dst */
> +	    (dst && dst_metric(dst, RTAX_QUICKACK)) ||
>  	    /* We have out of order data. */
>  	    (ofo_possible && skb_peek(&tp->out_of_order_queue))) {

This logic should be moved to tcp_in_quickack_mode() ?

Note I placed the dst test before others, to reduce jump prediction
misses.

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 684f095d196e..69ec8d25a2e5 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -196,11 +196,13 @@ static void tcp_enter_quickack_mode(struct sock *sk)
  * and the session is not interactive.
  */
 
-static inline bool tcp_in_quickack_mode(const struct sock *sk)
+static bool tcp_in_quickack_mode(struct sock *sk)
 {
 	const struct inet_connection_sock *icsk = inet_csk(sk);
+	const struct dst_entry *dst = __sk_dst_get(sk);
 
-	return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
+	return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
+	       (icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong);
 }
 
 static void tcp_ecn_queue_cwr(struct tcp_sock *tp)




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