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@nxp.com>
Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 839beb599f5572ff03516ab9cb9de405c4aafafb..9781b47962bbdea9fada1b1ee8997edcd25af124 100644 (file)
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -566,9 +566,6 @@ static int taprio_enqueue_one(struct sk_buff *skb, struct Qdisc *sch,
                        return qdisc_drop(skb, sch, to_free);
        }
 
-       if (taprio_skb_exceeds_queue_max_sdu(sch, skb))
-               return qdisc_drop(skb, sch, to_free);
-
        qdisc_qstats_backlog_inc(sch, skb);
        sch->q.qlen++;
 
@@ -593,7 +590,14 @@ static int taprio_enqueue_segmented(struct sk_buff *skb, struct Qdisc *sch,
                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 (taprio_skb_exceeds_queue_max_sdu(sch, segs))
+                       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);
@@ -625,13 +629,18 @@ 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);
+       if (taprio_skb_exceeds_queue_max_sdu(sch, skb)) {
+               /* 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);
+       }
 
        return taprio_enqueue_one(skb, sch, child, to_free);
 }