• Yuchung Cheng's avatar
    tcp: up initial rmem to 128KB and SYN rwin to around 64KB · a337531b
    Yuchung Cheng authored
    Previously TCP initial receive buffer is ~87KB by default and
    the initial receive window is ~29KB (20 MSS). This patch changes
    the two numbers to 128KB and ~64KB (rounding down to the multiples
    of MSS) respectively. The patch also simplifies the calculations s.t.
    the two numbers are directly controlled by sysctl tcp_rmem[1]:
    
      1) Initial receiver buffer budget (sk_rcvbuf): while this should
         be configured via sysctl tcp_rmem[1], previously tcp_fixup_rcvbuf()
         always override and set a larger size when a new connection
         establishes.
    
      2) Initial receive window in SYN: previously it is set to 20
         packets if MSS <= 1460. The number 20 was based on the initial
         congestion window of 10: the receiver needs twice amount to
         avoid being limited by the receive window upon out-of-order
         delivery in the first window burst. But since this only
         applies if the receiving MSS <= 1460, connection using large MTU
         (e.g. to utilize receiver zero-copy) may be limited by the
         receive window.
    
    With this patch TCP memory configuration is more straight-forward and
    more properly sized to modern high-speed networks by default. Several
    popular stacks have been announcing 64KB rwin in SYNs as well.
    Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
    Signed-off-by: default avatarWei Wang <weiwan@google.com>
    Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Reviewed-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    a337531b
tcp_output.c 108 KB