Merge branch 'tcp-plb'

Mubashir Adnan Qureshi says:

====================
net: Add PLB functionality to TCP

This patch series adds PLB (Protective Load Balancing) to TCP and hooks
it up to DCTCP. PLB is disabled by default and can be enabled using
relevant sysctls and support from underlying CC.

PLB (Protective Load Balancing) is a host based mechanism for load
balancing across switch links. It leverages congestion signals(e.g. ECN)
from transport layer to randomly change the path of the connection
experiencing congestion. PLB changes the path of the connection by
changing the outgoing IPv6 flow label for IPv6 connections (implemented
in Linux by calling sk_rethink_txhash()). Because of this implementation
mechanism, PLB can currently only work for IPv6 traffic. For more
information, see the SIGCOMM 2022 paper:
  https://doi.org/10.1145/3544216.3544226
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 1 deletions

diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c
index 2a6c0dd665a4..e0a2ca7456ff 100644
--- a/net/ipv4/tcp_dctcp.c
+++ b/net/ipv4/tcp_dctcp.c
@@ -54,6 +54,7 @@ struct dctcp {
 	u32 next_seq;
 	u32 ce_state;
 	u32 loss_cwnd;
+	struct tcp_plb_state plb;
 };
 
 static unsigned int dctcp_shift_g __read_mostly = 4; /* g = 1/2^4 */
@@ -91,6 +92,8 @@ static void dctcp_init(struct sock *sk)
 		ca->ce_state = 0;
 
 		dctcp_reset(tp, ca);
+		tcp_plb_init(sk, &ca->plb);
+
 		return;
 	}
 
@@ -117,14 +120,28 @@ static void dctcp_update_alpha(struct sock *sk, u32 flags)
 
 	/* Expired RTT */
 	if (!before(tp->snd_una, ca->next_seq)) {
+		u32 delivered = tp->delivered - ca->old_delivered;
 		u32 delivered_ce = tp->delivered_ce - ca->old_delivered_ce;
 		u32 alpha = ca->dctcp_alpha;
+		u32 ce_ratio = 0;
+
+		if (delivered > 0) {
+			/* dctcp_alpha keeps EWMA of fraction of ECN marked
+			 * packets. Because of EWMA smoothing, PLB reaction can
+			 * be slow so we use ce_ratio which is an instantaneous
+			 * measure of congestion. ce_ratio is the fraction of
+			 * ECN marked packets in the previous RTT.
+			 */
+			if (delivered_ce > 0)
+				ce_ratio = (delivered_ce << TCP_PLB_SCALE) / delivered;
+			tcp_plb_update_state(sk, &ca->plb, (int)ce_ratio);
+			tcp_plb_check_rehash(sk, &ca->plb);
+		}
 
 		/* alpha = (1 - g) * alpha + g * F */
 
 		alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g);
 		if (delivered_ce) {
-			u32 delivered = tp->delivered - ca->old_delivered;
 
 			/* If dctcp_shift_g == 1, a 32bit value would overflow
 			 * after 8 M packets.
@@ -172,8 +189,12 @@ static void dctcp_cwnd_event(struct sock *sk, enum tcp_ca_event ev)
 		dctcp_ece_ack_update(sk, ev, &ca->prior_rcv_nxt, &ca->ce_state);
 		break;
 	case CA_EVENT_LOSS:
+		tcp_plb_update_state_upon_rto(sk, &ca->plb);
 		dctcp_react_to_loss(sk);
 		break;
+	case CA_EVENT_TX_START:
+		tcp_plb_check_rehash(sk, &ca->plb); /* Maybe rehash when inflight is 0 */
+		break;
 	default:
 		/* Don't care for the rest. */
 		break;