0038-net-tcp_bbr-v2-inform-CC-module-of-losses-repaired-b.patch

From 2d36fbcc216d52a31aa10b7ffa18d68a4e91e38f Mon Sep 17 00:00:00 2001
From: Jianfeng Wang <jfwang@google.com>
Date: Tue, 16 Jun 2020 17:41:19 +0000
Subject: [PATCH 13/18] net-tcp_bbr: v2: inform CC module of losses repaired by
 TLP probe

Before this commit, when there is a packet loss that creates a sequence
hole that is filled by a TLP loss probe, then tcp_process_tlp_ack()
only informs the congestion control (CC) module via a back-to-back entry
and exit of CWR. But some congestion control modules (e.g. BBR) do not
respond to CWR events.

This commit adds a new CA event with which the core TCP stack notifies
the CC module when a loss is repaired by a TLP. This will allow CC
modules that do not use the CWR mechanism to have a custom handler for
such TLP recoveries.

Effort: net-tcp_bbr
Change-Id: Ieba72332b401b329bff5a641d2b2043a3fb8f632
Signed-off-by: Alexandre Frade <kernel@xanmod.org>
---
 include/net/tcp.h    | 1 +
 net/ipv4/tcp_input.c | 1 +
 2 files changed, 2 insertions(+)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index debdb13ca6b8..55513c3a44b3 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1010,6 +1010,7 @@ enum tcp_ca_event {
 	CA_EVENT_LOSS,		/* loss timeout */
 	CA_EVENT_ECN_NO_CE,	/* ECT set, but not CE marked */
 	CA_EVENT_ECN_IS_CE,	/* received CE marked IP packet */
+	CA_EVENT_TLP_RECOVERY,	/* a lost segment was repaired by TLP probe */
 };
 
 /* Information about inbound ACK, passed to cong_ops->in_ack_event() */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 85bebec5baac..879ebf7ca186 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3739,6 +3739,7 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
 		/* ACK advances: there was a loss, so reduce cwnd. Reset
 		 * tlp_high_seq in tcp_init_cwnd_reduction()
 		 */
+		tcp_ca_event(sk, CA_EVENT_TLP_RECOVERY);
 		tcp_init_cwnd_reduction(sk);
 		tcp_set_ca_state(sk, TCP_CA_CWR);
 		tcp_end_cwnd_reduction(sk);
-- 
2.39.2