• Gerrit Renker's avatar
    dccp: Deprecate Ack Ratio sysctl · dd9c0e36
    Gerrit Renker authored
    This patch deprecates the Ack Ratio sysctl, since
     * Ack Ratio is entirely ignored by CCID-3 and CCID-4,
     * Ack Ratio currently doesn't work in CCID-2 (i.e. is always set to 1);
     * even if it would work in CCID-2, there is no point for a user to change it:
       - Ack Ratio is constrained by cwnd (RFC 4341, 6.1.2),
       - if Ack Ratio > cwnd, the system resorts to spurious RTO timeouts
         (since waiting for Acks which will never arrive in this window),
       - cwnd is not a user-configurable value.
    
    The only reasonable place for Ack Ratio is to print it for debugging. It is
    planned to do this later on, as part of e.g. dccp_probe.
    
    With this patch Ack Ratio is now under full control of feature negotiation:
     * Ack Ratio is resolved as a dependency of the selected CCID;
     * if the chosen CCID supports it (i.e. CCID == CCID-2), Ack Ratio is set to
       the default of 2, following RFC 4340, 11.3 - "New connections start with Ack
       Ratio 2 for both endpoints";
     * what happens then is part of another patch set, since it concerns the
       dynamic update of Ack Ratio while the connection is in full flight.
    
    Thanks to Tomasz Grobelny for discussion leading up to this patch.
    Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
    Acked-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    dd9c0e36
sysctl.c 2.8 KB