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>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index a12f145..7ec6a28 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -763,8 +763,10 @@ enum tcp_ca_event {
        CA_EVENT_CWND_RESTART,  /* congestion window restart */
        CA_EVENT_COMPLETE_CWR,  /* end of congestion recovery */
        CA_EVENT_LOSS,          /* loss timeout */
-       CA_EVENT_FAST_ACK,      /* in sequence ack */
-       CA_EVENT_SLOW_ACK,      /* other ack */
+};
+
+enum tcp_ca_ack_event_flags {
+       CA_ACK_SLOWPATH = (1 << 0),
 };
 
 /*
@@ -796,6 +798,8 @@ struct tcp_congestion_ops {
        void (*set_state)(struct sock *sk, u8 new_state);
        /* call when cwnd event occurs (optional) */
        void (*cwnd_event)(struct sock *sk, enum tcp_ca_event ev);
+       /* call when ack arrives (optional) */
+       void (*in_ack_event)(struct sock *sk, u32 flags);
        /* new value of cwnd after loss (optional) */
        u32  (*undo_cwnd)(struct sock *sk);
        /* hook for packet ack accounting (optional) */

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index fb0fe97..8a38774 100644 (file)
--- 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 81911a9..bb63fba 100644 (file)
--- 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,