• Terry Lam's avatar
    net-qdisc-hhf: Heavy-Hitter Filter (HHF) qdisc · 10239edf
    Terry Lam authored
    This patch implements the first size-based qdisc that attempts to
    differentiate between small flows and heavy-hitters.  The goal is to
    catch the heavy-hitters and move them to a separate queue with less
    priority so that bulk traffic does not affect the latency of critical
    traffic.  Currently "less priority" means less weight (2:1 in
    particular) in a Weighted Deficit Round Robin (WDRR) scheduler.
    
    In essence, this patch addresses the "delay-bloat" problem due to
    bloated buffers. In some systems, large queues may be necessary for
    obtaining CPU efficiency, or due to the presence of unresponsive
    traffic like UDP, or just a large number of connections with each
    having a small amount of outstanding traffic. In these circumstances,
    HHF aims to reduce the HoL blocking for latency sensitive traffic,
    while not impacting the queues built up by bulk traffic.  HHF can also
    be used in conjunction with other AQM mechanisms such as CoDel.
    
    To capture heavy-hitters, we implement the "multi-stage filter" design
    in the following paper:
    C. Estan and G. Varghese, "New Directions in Traffic Measurement and
    Accounting", in ACM SIGCOMM, 2002.
    
    Some configurable qdisc settings through 'tc':
    - hhf_reset_timeout: period to reset counter values in the multi-stage
                         filter (default 40ms)
    - hhf_admit_bytes:   threshold to classify heavy-hitters
                         (default 128KB)
    - hhf_evict_timeout: threshold to evict idle heavy-hitters
                         (default 1s)
    - hhf_non_hh_weight: Weighted Deficit Round Robin (WDRR) weight for
                         non-heavy-hitters (default 2)
    - hh_flows_limit:    max number of heavy-hitter flow entries
                         (default 2048)
    
    Note that the ratio between hhf_admit_bytes and hhf_reset_timeout
    reflects the bandwidth of heavy-hitters that we attempt to capture
    (25Mbps with the above default settings).
    
    The false negative rate (heavy-hitter flows getting away unclassified)
    is zero by the design of the multi-stage filter algorithm.
    With 100 heavy-hitter flows, using four hashes and 4000 counters yields
    a false positive rate (non-heavy-hitters mistakenly classified as
    heavy-hitters) of less than 1e-4.
    Signed-off-by: default avatarTerry Lam <vtlam@google.com>
    Acked-by: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    10239edf
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