tcp: add cwnd_undo functions to various tcp cc algorithms
congestion control algorithms that do not halve cwnd in their .ssthresh
should provide a .cwnd_undo rather than rely on current fallback which
assumes reno halving (and thus doubles the cwnd).
All of these do 'something else' in their .ssthresh implementation, thus
store the cwnd on loss and provide .undo_cwnd to restore it again.
A followup patch will remove the fallback and all algorithms will
need to provide a .cwnd_undo function.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_veno.c b/net/ipv4/tcp_veno.c
index 40171e1..76005d4 100644
--- a/net/ipv4/tcp_veno.c
+++ b/net/ipv4/tcp_veno.c
@@ -30,6 +30,7 @@ struct veno {
u32 basertt; /* the min of all Veno rtt measurements seen (in usec) */
u32 inc; /* decide whether to increase cwnd */
u32 diff; /* calculate the diff rate */
+ u32 loss_cwnd; /* cwnd when loss occured */
};
/* There are several situations when we must "re-start" Veno:
@@ -193,6 +194,7 @@ static u32 tcp_veno_ssthresh(struct sock *sk)
const struct tcp_sock *tp = tcp_sk(sk);
struct veno *veno = inet_csk_ca(sk);
+ veno->loss_cwnd = tp->snd_cwnd;
if (veno->diff < beta)
/* in "non-congestive state", cut cwnd by 1/5 */
return max(tp->snd_cwnd * 4 / 5, 2U);
@@ -201,9 +203,17 @@ static u32 tcp_veno_ssthresh(struct sock *sk)
return max(tp->snd_cwnd >> 1U, 2U);
}
+static u32 tcp_veno_cwnd_undo(struct sock *sk)
+{
+ const struct veno *veno = inet_csk_ca(sk);
+
+ return max(tcp_sk(sk)->snd_cwnd, veno->loss_cwnd);
+}
+
static struct tcp_congestion_ops tcp_veno __read_mostly = {
.init = tcp_veno_init,
.ssthresh = tcp_veno_ssthresh,
+ .undo_cwnd = tcp_veno_cwnd_undo,
.cong_avoid = tcp_veno_cong_avoid,
.pkts_acked = tcp_veno_pkts_acked,
.set_state = tcp_veno_state,
