diff mbox series

[net-next,v2,2/2] tcp: change data receiver flowlabel after one dup

Message ID 20230929210352.3411495-3-morleyd.kernel@gmail.com (mailing list archive)
State Superseded
Delegated to: Netdev Maintainers
Headers show
Series tcp: save flowlabel and use for receiver repathing | expand

Checks

Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for net-next, async
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1343 this patch: 1343
netdev/cc_maintainers warning 2 maintainers not CCed: pabeni@redhat.com dsahern@kernel.org
netdev/build_clang success Errors and warnings before: 1364 this patch: 1364
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 1366 this patch: 1366
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 26 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

David Morley Sept. 29, 2023, 9:03 p.m. UTC 
From: David Morley <morleyd@google.com>

This commit changes the data receiver repath behavior to occur after
receiving a single duplicate. This can help recover ACK connectivity
quicker if a TLP was sent along a nonworking path.

For instance, consider the case where we have an initially nonworking
forward path and reverse path and subsequently switch to only working
forward paths. Before this patch we would have the following behavior.

+---------+--------+--------+----------+----------+----------+
| Event   | For FL | Rev FL | FP Works | RP Works | Data Del |
+---------+--------+--------+----------+----------+----------+
| Initial | A      | 1      | N        | N        | 0        |
+---------+--------+--------+----------+----------+----------+
| TLP     | A      | 1      | N        | N        | 0        |
+---------+--------+--------+----------+----------+----------+
| RTO 1   | B      | 1      | Y        | N        | 1        |
+---------+--------+--------+----------+----------+----------+
| RTO 2   | C      | 1      | Y        | N        | 2        |
+---------+--------+--------+----------+----------+----------+
| RTO 3   | D      | 2      | Y        | Y        | 3        |
+---------+--------+--------+----------+----------+----------+

This patch gets rid of at least RTO 3, avoiding additional unnecessary
repaths of a working forward path to a (potentially) nonworking one.

In addition, this commit changes the behavior to avoid repathing upon
rx of duplicate data if the local endpoint is in CA_Loss (in which
case the RTOs will already be changing the outgoing flowlabel).

Signed-off-by: David Morley <morleyd@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Tested-by: David Morley <morleyd@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
---
 net/ipv4/tcp_input.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)
diff mbox series

Patch

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index abe7494361c0..f77fbdb3103d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4511,15 +4511,23 @@  static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb)
 {
 	/* When the ACK path fails or drops most ACKs, the sender would
 	 * timeout and spuriously retransmit the same segment repeatedly.
-	 * The receiver remembers and reflects via DSACKs. Leverage the
-	 * DSACK state and change the txhash to re-route speculatively.
+	 * If it seems our ACKs are not reaching the other side,
+	 * based on receiving a duplicate data segment with new flowlabel
+	 * (suggesting the sender suffered an RTO), and we are not already
+	 * repathing due to our own RTO, then rehash the socket to repath our
+	 * packets.
 	 */
-	if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq &&
+#if IS_ENABLED(CONFIG_IPV6)
+	if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss &&
+	    skb->protocol == htons(ETH_P_IPV6) &&
+	    (tcp_sk(sk)->inet_conn.icsk_ack.lrcv_flowlabel !=
+	     ntohl(ip6_flowlabel(ipv6_hdr(skb)))) &&
 	    sk_rethink_txhash(sk))
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);
 
 	/* Save last flowlabel after a spurious retrans. */
 	tcp_save_lrcv_flowlabel(sk, skb);
+#endif
 }
 
 static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)