[openwrt/openwrt] kernel: merge a pending fix for HFSC warnings/slowdowns (fixes FS#1136)

[LEDE Commits]

nbd pushed a commit to openwrt/openwrt.git, branch lede-17.01:
https://git.lede-project.org/60f8d388c69e0faddbf1c3033cdcb74b38fe3694

commit 60f8d388c69e0faddbf1c3033cdcb74b38fe3694
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Sat Mar 10 10:09:07 2018 +0100

    kernel: merge a pending fix for HFSC warnings/slowdowns (fixes FS#1136)
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 ...ed-codel-do-not-defer-queue-length-update.patch | 86 ++++++++++++++++++++++
 .../patches-4.4/660-fq_codel_defaults.patch        |  2 +-
 .../patches-4.4/662-use_fq_codel_by_default.patch  |  4 +-
 3 files changed, 89 insertions(+), 3 deletions(-)

diff --git a/target/linux/generic/patches-4.4/620-net_sched-codel-do-not-defer-queue-length-update.patch b/target/linux/generic/patches-4.4/620-net_sched-codel-do-not-defer-queue-length-update.patch
new file mode 100644
index 0000000..2ec9c7a
--- /dev/null
+++ b/target/linux/generic/patches-4.4/620-net_sched-codel-do-not-defer-queue-length-update.patch
@@ -0,0 +1,86 @@
+From: Konstantin Khlebnikov <khlebnikov at yandex-team.ru>
+Date: Mon, 21 Aug 2017 11:14:14 +0300
+Subject: [PATCH] net_sched/codel: do not defer queue length update
+
+When codel wants to drop last packet in ->dequeue() it cannot call
+qdisc_tree_reduce_backlog() right away - it will notify parent qdisc
+about zero qlen and HTB/HFSC will deactivate class. The same class will
+be deactivated second time by caller of ->dequeue(). Currently codel and
+fq_codel defer update. This triggers warning in HFSC when it's qlen != 0
+but there is no active classes.
+
+This patch update parent queue length immediately: just temporary increase
+qlen around qdisc_tree_reduce_backlog() to prevent first class deactivation
+if we have skb to return.
+
+This might open another problem in HFSC - now operation peek could fail and
+deactivate parent class.
+
+Signed-off-by: Konstantin Khlebnikov <khlebnikov at yandex-team.ru>
+Link: https://bugzilla.kernel.org/show_bug.cgi?id=109581
+---
+
+--- a/net/sched/sch_codel.c
++++ b/net/sched/sch_codel.c
+@@ -79,11 +79,17 @@ static struct sk_buff *codel_qdisc_deque
+ 
+ 	skb = codel_dequeue(sch, &q->params, &q->vars, &q->stats, dequeue);
+ 
+-	/* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
+-	 * or HTB crashes. Defer it for next round.
++	/* If our qlen is 0 qdisc_tree_reduce_backlog() will deactivate
++	 * parent class, dequeue in parent qdisc will do the same if we
++	 * return skb. Temporary increment qlen if we have skb.
+ 	 */
+-	if (q->stats.drop_count && sch->q.qlen) {
+-		qdisc_tree_reduce_backlog(sch, q->stats.drop_count, q->stats.drop_len);
++	if (q->stats.drop_count) {
++		if (skb)
++			sch->q.qlen++;
++		qdisc_tree_reduce_backlog(sch, q->stats.drop_count,
++					  q->stats.drop_len);
++		if (skb)
++			sch->q.qlen--;
+ 		q->stats.drop_count = 0;
+ 		q->stats.drop_len = 0;
+ 	}
+--- a/net/sched/sch_fq_codel.c
++++ b/net/sched/sch_fq_codel.c
+@@ -311,6 +311,21 @@ begin:
+ 	flow->dropped += q->cstats.drop_count - prev_drop_count;
+ 	flow->dropped += q->cstats.ecn_mark - prev_ecn_mark;
+ 
++	/* If our qlen is 0 qdisc_tree_reduce_backlog() will deactivate
++	 * parent class, dequeue in parent qdisc will do the same if we
++	 * return skb. Temporary increment qlen if we have skb.
++	 */
++	if (q->cstats.drop_count) {
++		if (skb)
++			sch->q.qlen++;
++		qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
++					  q->cstats.drop_len);
++		if (skb)
++			sch->q.qlen--;
++		q->cstats.drop_count = 0;
++		q->cstats.drop_len = 0;
++	}
++
+ 	if (!skb) {
+ 		/* force a pass through old_flows to prevent starvation */
+ 		if ((head == &q->new_flows) && !list_empty(&q->old_flows))
+@@ -321,15 +336,6 @@ begin:
+ 	}
+ 	qdisc_bstats_update(sch, skb);
+ 	flow->deficit -= qdisc_pkt_len(skb);
+-	/* We cant call qdisc_tree_reduce_backlog() if our qlen is 0,
+-	 * or HTB crashes. Defer it for next round.
+-	 */
+-	if (q->cstats.drop_count && sch->q.qlen) {
+-		qdisc_tree_reduce_backlog(sch, q->cstats.drop_count,
+-					  q->cstats.drop_len);
+-		q->cstats.drop_count = 0;
+-		q->cstats.drop_len = 0;
+-	}
+ 	return skb;
+ }
+ 
diff --git a/target/linux/generic/patches-4.4/660-fq_codel_defaults.patch b/target/linux/generic/patches-4.4/660-fq_codel_defaults.patch
index 46fceff..fbe9008 100644
--- a/target/linux/generic/patches-4.4/660-fq_codel_defaults.patch
+++ b/target/linux/generic/patches-4.4/660-fq_codel_defaults.patch
@@ -1,6 +1,6 @@
 --- a/net/sched/sch_fq_codel.c
 +++ b/net/sched/sch_fq_codel.c
-@@ -471,7 +471,7 @@ static int fq_codel_init(struct Qdisc *s
+@@ -477,7 +477,7 @@ static int fq_codel_init(struct Qdisc *s
  
  	sch->limit = 10*1024;
  	q->flows_cnt = 1024;
diff --git a/target/linux/generic/patches-4.4/662-use_fq_codel_by_default.patch b/target/linux/generic/patches-4.4/662-use_fq_codel_by_default.patch
index 9d1962c..8d70b82 100644
--- a/target/linux/generic/patches-4.4/662-use_fq_codel_by_default.patch
+++ b/target/linux/generic/patches-4.4/662-use_fq_codel_by_default.patch
@@ -13,7 +13,7 @@
  	  device, it has to decide which ones to send first, which ones to
 --- a/net/sched/sch_fq_codel.c
 +++ b/net/sched/sch_fq_codel.c
-@@ -688,7 +688,7 @@ static const struct Qdisc_class_ops fq_c
+@@ -694,7 +694,7 @@ static const struct Qdisc_class_ops fq_c
  	.walk		=	fq_codel_walk,
  };
  
@@ -22,7 +22,7 @@
  	.cl_ops		=	&fq_codel_class_ops,
  	.id		=	"fq_codel",
  	.priv_size	=	sizeof(struct fq_codel_sched_data),
-@@ -704,6 +704,7 @@ static struct Qdisc_ops fq_codel_qdisc_o
+@@ -710,6 +710,7 @@ static struct Qdisc_ops fq_codel_qdisc_o
  	.dump_stats =	fq_codel_dump_stats,
  	.owner		=	THIS_MODULE,
  };