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authorEric Dumazet <edumazet@google.com>2018-11-20 05:53:59 -0800
committerDavid S. Miller <davem@davemloft.net>2018-11-21 15:49:52 -0800
commit86de5921a3d5dd246df661e09bdd0a6131b39ae3 (patch)
treeefa8b73f929d9a2e136aaa0e0fa1605d6c12ed1e /include
parentb5dd186d10ba59e6b5ba60e42b3b083df56df6f3 (diff)
tcp: defer SACK compression after DupThresh
Jean-Louis reported a TCP regression and bisected to recent SACK compression. After a loss episode (receiver not able to keep up and dropping packets because its backlog is full), linux TCP stack is sending a single SACK (DUPACK). Sender waits a full RTO timer before recovering losses. While RFC 6675 says in section 5, "Algorithm Details", (2) If DupAcks < DupThresh but IsLost (HighACK + 1) returns true -- indicating at least three segments have arrived above the current cumulative acknowledgment point, which is taken to indicate loss -- go to step (4). ... (4) Invoke fast retransmit and enter loss recovery as follows: there are old TCP stacks not implementing this strategy, and still counting the dupacks before starting fast retransmit. While these stacks probably perform poorly when receivers implement LRO/GRO, we should be a little more gentle to them. This patch makes sure we do not enable SACK compression unless 3 dupacks have been sent since last rcv_nxt update. Ideally we should even rearm the timer to send one or two more DUPACK if no more packets are coming, but that will be work aiming for linux-4.21. Many thanks to Jean-Louis for bisecting the issue, providing packet captures and testing this patch. Fixes: 5d9f4262b7ea ("tcp: add SACK compression") Reported-by: Jean-Louis Dupond <jean-louis@dupond.be> Tested-by: Jean-Louis Dupond <jean-louis@dupond.be> Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include')
-rw-r--r--include/linux/tcp.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 8ed77bb4ed86..a9b0280687d5 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -196,6 +196,7 @@ struct tcp_sock {
u32 rcv_tstamp; /* timestamp of last received ACK (for keepalives) */
u32 lsndtime; /* timestamp of last sent data packet (for restart window) */
u32 last_oow_ack_time; /* timestamp of last out-of-window ACK */
+ u32 compressed_ack_rcv_nxt;
u32 tsoffset; /* timestamp offset */