Commits
Merge branch 'tcp-undo-congestion' Yuchung Cheng says: ==================== undo congestion window on spurious SYN or SYNACK timeout Linux TCP currently uses the initial congestion window of 1 packet if multiple SYN or SYNACK timeouts per RFC6298. However such timeouts are often spurious on wireless or cellular networks that experience high delay variances (e.g. ramping up dormant radios or local link retransmission). Another case is when the underlying path is longer than the default SYN timeout (e.g. 1 second). In these cases starting the transfer with a minimal congestion window is detrimental to the performance for short flows. One naive approach is to simply ignore SYN or SYNACK timeouts and always use a larger or default initial window. This approach however risks pouring gas to the fire when the network is already highly congested. This is particularly true in data center where application could start thousands to millions of connections over a single or multiple hosts resulting in high SYN drops (e.g. incast). This patch-set detects spurious SYN and SYNACK timeouts upon completing the handshake via the widely-supported TCP timestamp options. Upon such events the sender reverts to the default initial window to start the data transfer so it gets best of both worlds. This patch-set supports this feature for both active and passive as well as Fast Open or regular connections. ==================== Signed-off-by: David S. Miller <davem@davemloft.net>
