@@ -1594,8 +1594,17 @@ hfsc_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free)
return err;
}
- if (cl->qdisc->q.qlen == 1)
+ if (cl->qdisc->q.qlen == 1) {
set_active(cl, qdisc_pkt_len(skb));
+ /*
+ * If this is the first packet, isolate the head so an eventual
+ * head drop before the first dequeue operation has no chance
+ * to invalidate the deadline.
+ */
+ if (cl->cl_flags & HFSC_RSC)
+ cl->qdisc->ops->peek(cl->qdisc);
+
+ }
qdisc_qstats_backlog_inc(sch, skb);
sch->q.qlen++;
Realtime scheduling implemented in HFSC uses head of the queue to make the decision about which packet to schedule next. But in case of any head drop, the deadline calculated for the previous head is not necessarily correct for the next head (unless both packets have the same length). Thanks to peek() function used during dequeue - which internally is a dequeue operation - hfsc is almost safe from this issue, as peek() dequeues and isolates the head storing it temporarily until the real dequeue happens. But there is one exception: if after the class activation a drop happens before the first dequeue operation, there's never a chance to do the peek(). Adding peek() call in enqueue - if this is the first packet in a new backlog period AND the scheduler has realtime curve defined - fixes that one corner case. The 1st hfsc_dequeue() will use that peeked packet, similarly as every subsequent hfsc_dequeue() call uses packet peeked by the previous call. Signed-off-by: Michal Soltys <soltys@ziu.info> --- net/sched/sch_hfsc.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)