• Kaike Wan's avatar
    IB/hfi1: Serve the most starved iowait entry first · bcad2913
    Kaike Wan authored
    When an egress resource(SDMA descriptors, pio credits) is not available,
    a sending thread will be put on the resource's wait queue. When the
    resource becomes available again, up to a fixed number of sending threads
    can be awakened sequentially and removed from the wait queue, depending
    on the number of waiting threads and the number of free resources. Since
    each awakened sending thread will send as many packets as possible, it
    is highly likely that the first sending thread will consume all the
    egress resources. Subsequently, it will be put back to the end of the wait
    queue. Depending on the timing when the later sending threads wake up,
    they may not be able to send any packet and be again put back to the end
    of the wait queue sequentially, right behind the first sending thread.
    This starvation cycle continues until some sending threads exceed their
    retry limit and consequently fail.
    
    This patch fixes the issue by two simple approaches:
    (1) Any starved sending thread will be put to the head of the wait queue
    while a served sending thread will be put to the tail;
    (2) The most starved sending thread will be served first.
    Reviewed-by: default avatarMike Marciniszyn <mike.marciniszyn@intel.com>
    Signed-off-by: default avatarKaike Wan <kaike.wan@intel.com>
    Signed-off-by: default avatarDennis Dalessandro <dennis.dalessandro@intel.com>
    Signed-off-by: default avatarDoug Ledford <dledford@redhat.com>
    bcad2913
qp.c 22.1 KB