net: tcp: split ack slow/fast events from cwnd_event

The congestion control ops "cwnd_event" currently supports
CA_EVENT_FAST_ACK and CA_EVENT_SLOW_ACK events (among others).
Both FAST and SLOW_ACK are only used by Westwood congestion
control algorithm.

This removes both flags from cwnd_event and adds a new
in_ack_event callback for this. The goal is to be able to
provide more detailed information about ACKs, such as whether
ECE flag was set, or whether the ACK resulted in a window
update.

It is required for DataCenter TCP (DCTCP) congestion control
algorithm as it makes a different choice depending on ECE being
set or not.

Joint work with Daniel Borkmann and Glenn Judd.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Glenn Judd <glenn.judd@morganstanley.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 26 insertions, 14 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index fb0fe97e1c54..8a38774cc66e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3362,6 +3362,14 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
         }
 }
 
+static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
+{
+        const struct inet_connection_sock *icsk = inet_csk(sk);
+
+        if (icsk->icsk_ca_ops->in_ack_event)
+                icsk->icsk_ca_ops->in_ack_event(sk, flags);
+}
+
 /* This routine deals with incoming acks, but not outgoing ones. */
 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 {
@@ -3421,7 +3429,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
                 tp->snd_una = ack;
                 flag |= FLAG_WIN_UPDATE;
 
-                tcp_ca_event(sk, CA_EVENT_FAST_ACK);
+                tcp_in_ack_event(sk, 0);
 
                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
         } else {
@@ -3439,7 +3447,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
                 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
                         flag |= FLAG_ECE;
 
-                tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
+                tcp_in_ack_event(sk, CA_ACK_SLOWPATH);
         }
 
         /* We passed data and got it acked, remove any soft error
diff --git a/net/ipv4/tcp_westwood.c b/net/ipv4/tcp_westwood.c
index 81911a92356c..bb63fba47d47 100644
--- a/net/ipv4/tcp_westwood.c
+++ b/net/ipv4/tcp_westwood.c
@@ -220,32 +220,35 @@ static u32 tcp_westwood_bw_rttmin(const struct sock *sk)
         return max_t(u32, (w->bw_est * w->rtt_min) / tp->mss_cache, 2);
 }
 
+static void tcp_westwood_ack(struct sock *sk, u32 ack_flags)
+{
+        if (ack_flags & CA_ACK_SLOWPATH) {
+                struct westwood *w = inet_csk_ca(sk);
+
+                westwood_update_window(sk);
+                w->bk += westwood_acked_count(sk);
+
+                update_rtt_min(w);
+                return;
+        }
+
+        westwood_fast_bw(sk);
+}
+
 static void tcp_westwood_event(struct sock *sk, enum tcp_ca_event event)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         struct westwood *w = inet_csk_ca(sk);
 
         switch (event) {
-        case CA_EVENT_FAST_ACK:
-                westwood_fast_bw(sk);
-                break;
-
         case CA_EVENT_COMPLETE_CWR:
                 tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
                 break;
-
         case CA_EVENT_LOSS:
                 tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
                 /* Update RTT_min when next ack arrives */
                 w->reset_rtt_min = 1;
                 break;
-
-        case CA_EVENT_SLOW_ACK:
-                westwood_update_window(sk);
-                w->bk += westwood_acked_count(sk);
-                update_rtt_min(w);
-                break;
-
         default:
                 /* don't care */
                 break;
@@ -274,6 +277,7 @@ static struct tcp_congestion_ops tcp_westwood __read_mostly = {
         .ssthresh       = tcp_reno_ssthresh,
         .cong_avoid     = tcp_reno_cong_avoid,
         .cwnd_event     = tcp_westwood_event,
+        .in_ack_event   = tcp_westwood_ack,
         .get_info       = tcp_westwood_info,
         .pkts_acked     = tcp_westwood_pkts_acked,