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2072c228c9
When a delayed ACK representing two packets arrives, there are two RTT samples available, one for each packet. The first (in order of seq number) will be artificially long due to the delay waiting for the second packet, the second will trigger the ACK and so will not itself be delayed. According to rfc1323, the SRTT used for RTO calculation should use the first rtt, so receivers echo the timestamp from the first packet in the delayed ack. For congestion control however, it seems measuring delayed ack delay is not desirable as it varies independently of congestion. The patch below causes seq_rtt and last_ackt to be updated with any available later packet rtts which should have less (and hopefully zero) delack delay. The rtt value then gets passed to ca_ops->pkts_acked(). Where TCP_CONG_RTT_STAMP was set, effort was made to supress RTTs from within a TSO chunk (!fully_acked), using only the final ACK (which includes any TSO delay) to generate RTTs. This patch removes these checks so RTTs are passed for each ACK to ca_ops->pkts_acked(). For non-delay based congestion control (cubic, h-tcp), rtt is sometimes used for rtt-scaling. In shortening the RTT, this may make them a little less aggressive. Delay-based schemes (eg vegas, veno, illinois) should get a cleaner, more accurate congestion signal, particularly for small cwnds. The congestion control module can potentially also filter out bad RTTs due to the delayed ack alarm by looking at the associated cnt which (where delayed acking is in use) should probably be 1 if the alarm went off or greater if the ACK was triggered by a packet. Signed-off-by: Gavin McCullagh <gavin.mccullagh@nuim.ie> Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net> |
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