• Florian Westphal's avatar
    mptcp: add receive buffer auto-tuning · a6b118fe
    Florian Westphal authored
    When mptcp is used, userspace doesn't read from the tcp (subflow)
    socket but from the parent (mptcp) socket receive queue.
    
    skbs are moved from the subflow socket to the mptcp rx queue either from
    'data_ready' callback (if mptcp socket can be locked), a work queue, or
    the socket receive function.
    
    This means tcp_rcv_space_adjust() is never called and thus no receive
    buffer size auto-tuning is done.
    
    An earlier (not merged) patch added tcp_rcv_space_adjust() calls to the
    function that moves skbs from subflow to mptcp socket.
    While this enabled autotuning, it also meant tuning was done even if
    userspace was reading the mptcp socket very slowly.
    
    This adds mptcp_rcv_space_adjust() and calls it after userspace has
    read data from the mptcp socket rx queue.
    
    Its very similar to tcp_rcv_space_adjust, with two differences:
    
    1. The rtt estimate is the largest one observed on a subflow
    2. The rcvbuf size and window clamp of all subflows is adjusted
       to the mptcp-level rcvbuf.
    
    Otherwise, we get spurious drops at tcp (subflow) socket level if
    the skbs are not moved to the mptcp socket fast enough.
    
    Before:
    time mptcp_connect.sh -t -f $((4*1024*1024)) -d 300 -l 0.01% -r 0 -e "" -m mmap
    [..]
    ns4 MPTCP -> ns3 (10.0.3.2:10108      ) MPTCP   (duration 40823ms) [ OK ]
    ns4 MPTCP -> ns3 (10.0.3.2:10109      ) TCP     (duration 23119ms) [ OK ]
    ns4 TCP   -> ns3 (10.0.3.2:10110      ) MPTCP   (duration  5421ms) [ OK ]
    ns4 MPTCP -> ns3 (dead:beef:3::2:10111) MPTCP   (duration 41446ms) [ OK ]
    ns4 MPTCP -> ns3 (dead:beef:3::2:10112) TCP     (duration 23427ms) [ OK ]
    ns4 TCP   -> ns3 (dead:beef:3::2:10113) MPTCP   (duration  5426ms) [ OK ]
    Time: 1396 seconds
    
    After:
    ns4 MPTCP -> ns3 (10.0.3.2:10108      ) MPTCP   (duration  5417ms) [ OK ]
    ns4 MPTCP -> ns3 (10.0.3.2:10109      ) TCP     (duration  5427ms) [ OK ]
    ns4 TCP   -> ns3 (10.0.3.2:10110      ) MPTCP   (duration  5422ms) [ OK ]
    ns4 MPTCP -> ns3 (dead:beef:3::2:10111) MPTCP   (duration  5415ms) [ OK ]
    ns4 MPTCP -> ns3 (dead:beef:3::2:10112) TCP     (duration  5422ms) [ OK ]
    ns4 TCP   -> ns3 (dead:beef:3::2:10113) MPTCP   (duration  5423ms) [ OK ]
    Time: 296 seconds
    Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
    Reviewed-by: default avatarMatthieu Baerts <matthieu.baerts@tessares.net>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    a6b118fe
subflow.c 34.3 KB