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authorNeal Cardwell <ncardwell@google.com>2021-07-27 16:42:58 +0200
committerDavid S. Miller <davem@davemloft.net>2021-07-27 21:07:21 +0200
commita657db0350bb8f568897835b6189c84a89f13292 (patch)
tree40699aa991aa192060e472048665088a7029bfd1 /net/ipv4/tcp_input.c
parenttcp: more accurately detect spurious TLP probes (diff)
downloadlinux-a657db0350bb8f568897835b6189c84a89f13292.tar.xz
linux-a657db0350bb8f568897835b6189c84a89f13292.zip
tcp: more accurately check DSACKs to grow RACK reordering window
Previously, a DSACK could expand the RACK reordering window when no reordering has been seen, and/or when the DSACK was due to an unnecessary TLP retransmit (rather than a spurious fast recovery due to reordering). This could result in unnecessarily growing the RACK reordering window and thus unnecessarily delaying RACK-based fast recovery episodes. To avoid these issues, this commit tightens the conditions under which a DSACK triggers the RACK reordering window to grow, so that a connection only expands its RACK reordering window if: (a) reordering has been seen in the connection (b) a DSACKed range does not match the most recent TLP retransmit Signed-off-by: Neal Cardwell <ncardwell@google.com> Acked-by: Yuchung Cheng <ycheng@google.com> Acked-by: Priyaranjan Jha <priyarjha@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_input.c')
-rw-r--r--net/ipv4/tcp_input.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 98408d520c32..3f7bd7ae7d7a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1001,7 +1001,14 @@ static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq,
return 0;
tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
- tp->rack.dsack_seen = 1;
+ /* We increase the RACK ordering window in rounds where we receive
+ * DSACKs that may have been due to reordering causing RACK to trigger
+ * a spurious fast recovery. Thus RACK ignores DSACKs that happen
+ * without having seen reordering, or that match TLP probes (TLP
+ * is timer-driven, not triggered by RACK).
+ */
+ if (tp->reord_seen && !(state->flag & FLAG_DSACK_TLP))
+ tp->rack.dsack_seen = 1;
state->flag |= FLAG_DSACKING_ACK;
/* A spurious retransmission is delivered */