git: tcp/sack: Force out more segments allowed by "pipe" during fast recovery

[Sepherosa Ziehau]

commit ccb518eadb169585edd353b50b1d0f665b45c3ee
Author: Sepherosa Ziehau <sephe at dragonflybsd.org>
Date:   Thu May 24 16:09:57 2012 +0800

    tcp/sack: Force out more segments allowed by "pipe" during fast recovery
    
    If some segments are cumulatively acked or SACKed, and HighRxt equals
    snd_una, one segment (new or retransmit) will be forced out even if cwnd
    and pipe don't allow it.  When large amount of segments are lost, i.e.
    computed pipe could be large, this avoids unnecessary retransmit timeout
    and could perform as good as NewReno.
    
    Sysctl node net.inet.tcp.force_sackrxt could be tuned to burst out several
    retransmits, default is 1 (should be good enough).  Set this sysctl to 0,
    SACK based fast recovery will obey the computed pipe.
    
    Several unnecessary retransmit timeout graph as described above:
    http://leaf.dragonflybsd.org/~sephe/no_force_sack_rexmt2_15.xpl (starts @15s)
    http://leaf.dragonflybsd.org/~sephe/no_force_sack_rexmt_54.xpl (starts @54s)

Summary of changes:
 sys/netinet/tcp_input.c |   43 +++++++++++++++++++++++++++++++++++++------
 sys/netinet/tcp_sack.c  |   20 +++++++++++++++++++-
 sys/netinet/tcp_var.h   |    1 +
 3 files changed, 57 insertions(+), 7 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/ccb518eadb169585edd353b50b1d0f665b45c3ee


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