• Yuchung Cheng's avatar
    tcp: properly handle stretch acks in slow start · 9f9843a7
    Yuchung Cheng authored
    
    
    Slow start now increases cwnd by 1 if an ACK acknowledges some packets,
    regardless the number of packets. Consequently slow start performance
    is highly dependent on the degree of the stretch ACKs caused by
    receiver or network ACK compression mechanisms (e.g., delayed-ACK,
    GRO, etc).  But slow start algorithm is to send twice the amount of
    packets of packets left so it should process a stretch ACK of degree
    N as if N ACKs of degree 1, then exits when cwnd exceeds ssthresh. A
    follow up patch will use the remainder of the N (if greater than 1)
    to adjust cwnd in the congestion avoidance phase.
    
    In addition this patch retires the experimental limited slow start
    (LSS) feature. LSS has multiple drawbacks but questionable benefit. The
    fractional cwnd increase in LSS requires a loop in slow start even
    though it's rarely used. Configuring such an increase step via a global
    sysctl on different BDPS seems hard. Finally and most importantly the
    slow start overshoot concern is now better covered by the Hybrid slow
    start (hystart) enabled by default.
    Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
    Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    9f9843a7
tcp_yeah.c 6.92 KB