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>

1 files changed, 6 insertions, 2 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index a12f145cfbc3..7ec6a28305c0 100644
--- 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) */