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In presence of inelastic flows and stress, we can call fq_codel_drop() for every packet entering fq_codel qdisc. fq_codel_drop() is quite expensive, as it does a linear scan of 4 KB of memory to find a fat flow. Once found, it drops the oldest packet of this flow. Instead of dropping a single packet, try to drop 50% of the backlog of this fat flow, with a configurable limit of 64 packets per round. TCA_FQ_CODEL_DROP_BATCH_SIZE is the new attribute to make this limit configurable. With this strategy the 4 KB search is amortized to a single cache line per drop [1], so fq_codel_drop() no longer appears at the top of kernel profile in presence of few inelastic flows. [1] Assuming a 64byte cache line, and 1024 buckets Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Dave Taht <dave.taht@gmail.com> Cc: Jonathan Morton <chromatix99@gmail.com> Acked-by: Jesper Dangaard Brouer <brouer@redhat.com> Acked-by: Dave Taht Signed-off-by: David S. Miller <davem@davemloft.net> |
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