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Date: Sat, 28 Jan 2023 03:07:19 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: netdev@...r.kernel.org
Cc: Vinicius Costa Gomes <vinicius.gomes@...el.com>,
Kurt Kanzenbach <kurt@...utronix.de>
Subject: [RFC PATCH net-next 15/15] net/sched: taprio: don't segment unnecessarily
Improve commit 497cc00224cf ("taprio: Handle short intervals and large
packets") to only perform segmentation when skb->len exceeds what
taprio_dequeue() expects.
In practice, this will make the biggest difference when a traffic class
gate is always open in the schedule. This is because the max_frm_len
will be U32_MAX, and such large skb->len values as Kurt reported will be
sent just fine unsegmented.
What I don't seem to know how to handle is how to make sure that the
segmented skbs themselves are smaller than the maximum frame size given
by the current queueMaxSDU[tc]. Nonetheless, we still need to drop
those, otherwise the Qdisc will hang.
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
net/sched/sch_taprio.c | 67 ++++++++++++++++++++++++++----------------
1 file changed, 42 insertions(+), 25 deletions(-)
diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index cc11787dc62a..e0bd613a6415 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -527,10 +527,6 @@ static int taprio_enqueue_one(struct sk_buff *skb, struct Qdisc *sch,
struct Qdisc *child, struct sk_buff **to_free)
{
struct taprio_sched *q = qdisc_priv(sch);
- struct net_device *dev = qdisc_dev(sch);
- struct sched_gate_list *sched;
- int prio = skb->priority;
- u8 tc;
/* sk_flags are only safe to use on full sockets. */
if (skb->sk && sk_fullsock(skb->sk) && sock_flag(skb->sk, SOCK_TXTIME)) {
@@ -542,17 +538,6 @@ static int taprio_enqueue_one(struct sk_buff *skb, struct Qdisc *sch,
return qdisc_drop(skb, sch, to_free);
}
- /* Devices with full offload are expected to honor this in hardware */
- tc = netdev_get_prio_tc_map(dev, prio);
-
- rcu_read_lock();
- sched = rcu_dereference(q->oper_sched);
- if (sched && skb->len > sched->max_frm_len[tc]) {
- rcu_read_unlock();
- return qdisc_drop(skb, sch, to_free);
- }
- rcu_read_unlock();
-
qdisc_qstats_backlog_inc(sch, skb);
sch->q.qlen++;
@@ -565,19 +550,34 @@ static int taprio_enqueue_segmented(struct sk_buff *skb, struct Qdisc *sch,
{
unsigned int slen = 0, numsegs = 0, len = qdisc_pkt_len(skb);
netdev_features_t features = netif_skb_features(skb);
+ struct taprio_sched *q = qdisc_priv(sch);
+ struct net_device *dev = qdisc_dev(sch);
+ struct sched_gate_list *sched;
struct sk_buff *segs, *nskb;
- int ret;
+ int tc, ret;
+
+ tc = netdev_get_prio_tc_map(dev, skb->priority);
segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK);
if (IS_ERR_OR_NULL(segs))
return qdisc_drop(skb, sch, to_free);
+ rcu_read_lock();
+ sched = rcu_dereference(q->oper_sched);
+
skb_list_walk_safe(segs, segs, nskb) {
skb_mark_not_on_list(segs);
qdisc_skb_cb(segs)->pkt_len = segs->len;
slen += segs->len;
- ret = taprio_enqueue_one(segs, sch, child, to_free);
+ /* FIXME: we should be segmenting to a smaller size
+ * rather than dropping these
+ */
+ if (sched && skb->len > sched->max_frm_len[tc])
+ ret = qdisc_drop(segs, sch, to_free);
+ else
+ ret = taprio_enqueue_one(segs, sch, child, to_free);
+
if (ret != NET_XMIT_SUCCESS) {
if (net_xmit_drop_count(ret))
qdisc_qstats_drop(sch);
@@ -586,6 +586,8 @@ static int taprio_enqueue_segmented(struct sk_buff *skb, struct Qdisc *sch,
}
}
+ rcu_read_unlock();
+
if (numsegs > 1)
qdisc_tree_reduce_backlog(sch, 1 - numsegs, len - slen);
consume_skb(skb);
@@ -600,8 +602,11 @@ static int taprio_enqueue(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free)
{
struct taprio_sched *q = qdisc_priv(sch);
+ struct net_device *dev = qdisc_dev(sch);
+ struct sched_gate_list *sched;
+ int prio = skb->priority;
struct Qdisc *child;
- int queue;
+ int tc, queue;
queue = skb_get_queue_mapping(skb);
@@ -609,13 +614,25 @@ static int taprio_enqueue(struct sk_buff *skb, struct Qdisc *sch,
if (unlikely(!child))
return qdisc_drop(skb, sch, to_free);
- /* Large packets might not be transmitted when the transmission duration
- * exceeds any configured interval. Therefore, segment the skb into
- * smaller chunks. Drivers with full offload are expected to handle
- * this in hardware.
- */
- if (skb_is_gso(skb))
- return taprio_enqueue_segmented(skb, sch, child, to_free);
+ /* Devices with full offload are expected to honor this in hardware */
+ tc = netdev_get_prio_tc_map(dev, prio);
+
+ rcu_read_lock();
+ sched = rcu_dereference(q->oper_sched);
+ if (sched && skb->len > sched->max_frm_len[tc]) {
+ rcu_read_unlock();
+ /* Large packets might not be transmitted when the transmission duration
+ * exceeds any configured interval. Therefore, segment the skb into
+ * smaller chunks. Drivers with full offload are expected to handle
+ * this in hardware.
+ */
+ if (skb_is_gso(skb))
+ return taprio_enqueue_segmented(skb, sch, child,
+ to_free);
+
+ return qdisc_drop(skb, sch, to_free);
+ }
+ rcu_read_unlock();
return taprio_enqueue_one(skb, sch, child, to_free);
}
--
2.34.1
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