• Jon Maloy's avatar
    tipc: reduce risk of wakeup queue starvation · 7c5b4205
    Jon Maloy authored
    In commit 365ad353 ("tipc: reduce risk of user starvation during
    link congestion") we allowed senders to add exactly one list of extra
    buffers to the link backlog queues during link congestion (aka
    "oversubscription"). However, the criteria for when to stop adding
    wakeup messages to the input queue when the overload abates is
    inaccurate, and may cause starvation problems during very high load.
    
    Currently, we stop adding wakeup messages after 10 total failed attempts
    where we find that there is no space left in the backlog queue for a
    certain importance level. The counter for this is accumulated across all
    levels, which may lead the algorithm to leave the loop prematurely,
    although there may still be plenty of space available at some levels.
    The result is sometimes that messages near the wakeup queue tail are not
    added to the input queue as they should be.
    
    We now introduce a more exact algorithm, where we keep adding wakeup
    messages to a level as long as the backlog queue has free slots for
    the corresponding level, and stop at the moment there are no more such
    slots or when there are no more wakeup messages to dequeue.
    
    Fixes: 365ad353 ("tipc: reduce risk of user starvation during link congestion")
    Reported-by: default avatarTung Nguyen <tung.q.nguyen@dektech.com.au>
    Acked-by: default avatarYing Xue <ying.xue@windriver.com>
    Signed-off-by: default avatarJon Maloy <jon.maloy@ericsson.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    7c5b4205
link.c 75 KB