• Yuchung Cheng's avatar
    tcp: new CC hook to set sending rate with rate_sample in any CA state · c0402760
    Yuchung Cheng authored
    This commit introduces an optional new "omnipotent" hook,
    cong_control(), for congestion control modules. The cong_control()
    function is called at the end of processing an ACK (i.e., after
    updating sequence numbers, the SACK scoreboard, and loss
    detection). At that moment we have precise delivery rate information
    the congestion control module can use to control the sending behavior
    (using cwnd, TSO skb size, and pacing rate) in any CA state.
    
    This function can also be used by a congestion control that prefers
    not to use the default cwnd reduction approach (i.e., the PRR
    algorithm) during CA_Recovery to control the cwnd and sending rate
    during loss recovery.
    
    We take advantage of the fact that recent changes defer the
    retransmission or transmission of new data (e.g. by F-RTO) in recovery
    until the new tcp_cong_control() function is run.
    
    With this commit, we only run tcp_update_pacing_rate() if the
    congestion control is not using this new API. New congestion controls
    which use the new API do not want the TCP stack to run the default
    pacing rate calculation and overwrite whatever pacing rate they have
    chosen at initialization time.
    Signed-off-by: default avatarVan Jacobson <vanj@google.com>
    Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
    Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
    Signed-off-by: default avatarNandita Dukkipati <nanditad@google.com>
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    c0402760
tcp_cong.c 10.9 KB