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From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
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Date: Mon, 21 Aug 2017 11:14:14 +0300
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Subject: [PATCH] net_sched/codel: do not defer queue length update
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When codel wants to drop last packet in ->dequeue() it cannot call
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qdisc_tree_reduce_backlog() right away - it will notify parent qdisc
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about zero qlen and HTB/HFSC will deactivate class. The same class will
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be deactivated second time by caller of ->dequeue(). Currently codel and
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fq_codel defer update. This triggers warning in HFSC when it's qlen != 0
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but there is no active classes.
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This patch update parent queue length immediately: just temporary increase
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qlen around qdisc_tree_reduce_backlog() to prevent first class deactivation
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if we have skb to return.
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This might open another problem in HFSC - now operation peek could fail and
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deactivate parent class.
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Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
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Link: https://bugzilla.kernel.org/show_bug.cgi?id=109581
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---
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--- a/net/sched/sch_codel.c
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+++ b/net/sched/sch_codel.c
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@@ -95,11 +95,17 @@ static struct sk_buff *codel_qdisc_deque
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&q->stats, qdisc_pkt_len, codel_get_enqueue_time,
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drop_func, dequeue_func);
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- /* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
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- * or HTB crashes. Defer it for next round.
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+ /* If our qlen is 0 qdisc_tree_reduce_backlog() will deactivate
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+ * parent class, dequeue in parent qdisc will do the same if we
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+ * return skb. Temporary increment qlen if we have skb.
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*/
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- if (q->stats.drop_count && sch->q.qlen) {
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- qdisc_tree_reduce_backlog(sch, q->stats.drop_count, q->stats.drop_len);
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+ if (q->stats.drop_count) {
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+ if (skb)
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+ sch->q.qlen++;
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+ qdisc_tree_reduce_backlog(sch, q->stats.drop_count,
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+ q->stats.drop_len);
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+ if (skb)
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+ sch->q.qlen--;
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q->stats.drop_count = 0;
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q->stats.drop_len = 0;
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}
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--- a/net/sched/sch_fq_codel.c
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+++ b/net/sched/sch_fq_codel.c
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@@ -317,6 +317,21 @@ begin:
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flow->dropped += q->cstats.drop_count - prev_drop_count;
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flow->dropped += q->cstats.ecn_mark - prev_ecn_mark;
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+ /* If our qlen is 0 qdisc_tree_reduce_backlog() will deactivate
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+ * parent class, dequeue in parent qdisc will do the same if we
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+ * return skb. Temporary increment qlen if we have skb.
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+ */
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+ if (q->cstats.drop_count) {
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+ if (skb)
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+ sch->q.qlen++;
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+ qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
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+ q->cstats.drop_len);
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+ if (skb)
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+ sch->q.qlen--;
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+ q->cstats.drop_count = 0;
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+ q->cstats.drop_len = 0;
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+ }
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+
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if (!skb) {
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/* force a pass through old_flows to prevent starvation */
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if ((head == &q->new_flows) && !list_empty(&q->old_flows))
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@@ -327,15 +342,6 @@ begin:
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}
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qdisc_bstats_update(sch, skb);
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flow->deficit -= qdisc_pkt_len(skb);
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- /* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
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- * or HTB crashes. Defer it for next round.
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- */
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- if (q->cstats.drop_count && sch->q.qlen) {
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- qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
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- q->cstats.drop_len);
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- q->cstats.drop_count = 0;
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- q->cstats.drop_len = 0;
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- }
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return skb;
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}
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