• David Howells's avatar
    rxrpc: Fix the excessive initial retransmission timeout · c410bf01
    David Howells authored
    rxrpc currently uses a fixed 4s retransmission timeout until the RTT is
    sufficiently sampled.  This can cause problems with some fileservers with
    calls to the cache manager in the afs filesystem being dropped from the
    fileserver because a packet goes missing and the retransmission timeout is
    greater than the call expiry timeout.
    
    Fix this by:
    
     (1) Copying the RTT/RTO calculation code from Linux's TCP implementation
         and altering it to fit rxrpc.
    
     (2) Altering the various users of the RTT to make use of the new SRTT
         value.
    
     (3) Replacing the use of rxrpc_resend_timeout to use the calculated RTO
         value instead (which is needed in jiffies), along with a backoff.
    
    Notes:
    
     (1) rxrpc provides RTT samples by matching the serial numbers on outgoing
         DATA packets that have the RXRPC_REQUEST_ACK set and PING ACK packets
         against the reference serial number in incoming REQUESTED ACK and
         PING-RESPONSE ACK packets.
    
     (2) Each packet that is transmitted on an rxrpc connection gets a new
         per-connection serial number, even for retransmissions, so an ACK can
         be cross-referenced to a specific trigger packet.  This allows RTT
         information to be drawn from retransmitted DATA packets also.
    
     (3) rxrpc maintains the RTT/RTO state on the rxrpc_peer record rather than
         on an rxrpc_call because many RPC calls won't live long enough to
         generate more than one sample.
    
     (4) The calculated SRTT value is in units of 8ths of a microsecond rather
         than nanoseconds.
    
    The (S)RTT and RTO values are displayed in /proc/net/rxrpc/peers.
    
    Fixes: 17926a79 ([AF_RXRPC]: Provide secure RxRPC sockets for use by userspace and kernel both"")
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    c410bf01
call_accept.c 18.4 KB