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sch_sfq: dont put new flow at the end of flows

SFQ enqueue algo puts a new flow _behind_ all pre-existing flows in the
circular list. In fact this is probably an old SFQ implementation bug.

100 Mbits = ~8333 full frames per second, or ~8 frames per ms.

With 50 flows, it means your "new flow" will have to wait 50 packets
being sent before its own packet. Thats the ~6ms.

We certainly can change SFQ to give a priority advantage to new flows,
so that next dequeued packet is taken from a new flow, not an old one.

Reported-by: Dave Taht <dave.taht@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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1 parent 1c015b3 commit d47a0ac7b66883987275598d6039f902f4410ca9 Eric Dumazet committed with davem330 Jan 1, 2012
Showing with 1 addition and 1 deletion.
  1. +1 −1 net/sched/sch_sfq.c
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@@ -366,11 +366,11 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
if (slot->qlen == 1) { /* The flow is new */
if (q->tail == NULL) { /* It is the first flow */
slot->next = x;
+ q->tail = slot;
} else {
slot->next = q->tail->next;
q->tail->next = x;
}
- q->tail = slot;
slot->allot = q->scaled_quantum;
}
if (++sch->q.qlen <= q->limit)

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