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94bdc9785a
This patch disables FACK by default as RACK is the successor of FACK (inspired by the insights behind FACK). FACK[1] in Linux works as follows: a packet P is deemed lost, if packet Q of higher sequence is s/acked and P and Q are distant by at least dupthresh number of packets in sequence space. FACK is more aggressive than the IETF recommened recovery for SACK (RFC3517 A Conservative Selective Acknowledgment (SACK)-based Loss Recovery Algorithm for TCP), because a single SACK may trigger fast recovery. This obviously won't work well with reordering so FACK is dynamically disabled upon detecting reordering. RACK supersedes FACK by using time distance instead of sequence distance. On reordering, RACK waits for a quarter of RTT receiving a single SACK before starting recovery. (the timer can be made more adaptive in the future by measuring reordering distance in time, but currently RTT/4 seem to work well.) Once the recovery starts, RACK behaves almost like FACK because it reduces the reodering window to 1ms, so it fast retransmits quickly. In addition RACK can detect loss retransmission as it does not care about the packet sequences (being repeated or not), which is extremely useful when the connection is going through a traffic policer. Google server experiments indicate that disabling FACK after enabling RACK has negligible impact on the overall loss recovery performance with more reordering events detected. But we still keep the FACK implementation for backup if RACK has bugs that needs to be disabled. [1] M. Mathis, J. Mahdavi, "Forward Acknowledgment: Refining TCP Congestion Control," In Proceedings of SIGCOMM '96, August 1996. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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| 6lowpan | ||
| 9p | ||
| 802 | ||
| 8021q | ||
| appletalk | ||
| atm | ||
| ax25 | ||
| batman-adv | ||
| bluetooth | ||
| bridge | ||
| caif | ||
| can | ||
| ceph | ||
| core | ||
| dcb | ||
| dccp | ||
| decnet | ||
| dns_resolver | ||
| dsa | ||
| ethernet | ||
| hsr | ||
| ieee802154 | ||
| ipv4 | ||
| ipv6 | ||
| ipx | ||
| irda | ||
| iucv | ||
| kcm | ||
| key | ||
| l2tp | ||
| l3mdev | ||
| lapb | ||
| llc | ||
| mac80211 | ||
| mac802154 | ||
| mpls | ||
| ncsi | ||
| netfilter | ||
| netlabel | ||
| netlink | ||
| netrom | ||
| nfc | ||
| openvswitch | ||
| packet | ||
| phonet | ||
| qrtr | ||
| rds | ||
| rfkill | ||
| rose | ||
| rxrpc | ||
| sched | ||
| sctp | ||
| smc | ||
| strparser | ||
| sunrpc | ||
| switchdev | ||
| tipc | ||
| unix | ||
| vmw_vsock | ||
| wimax | ||
| wireless | ||
| x25 | ||
| xfrm | ||
| compat.c | ||
| Kconfig | ||
| Makefile | ||
| socket.c | ||
| sysctl_net.c | ||