net: netem: use a list in addition to rbtree
When testing high-bandwidth TCP streams with large windows, high latency, and low jitter, netem consumes a lot of CPU cycles doing rbtree rebalancing. This patch uses a linear list/queue in addition to the rbtree: if an incoming packet is past the tail of the linear queue, it is added there, otherwise it is inserted into the rbtree. Without this patch, perf shows netem_enqueue, netem_dequeue, and rb_* functions among the top offenders. With this patch, only netem_enqueue is noticeable if jitter is low/absent. Suggested-by: NEric Dumazet <edumazet@google.com> Signed-off-by: NPeter Oskolkov <posk@google.com> Reviewed-by: NEric Dumazet <edumazet@google.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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