net: sched: pfifo_fast use skb_array

This converts the pfifo_fast qdisc to use the skb_array data structure
and set the lockless qdisc bit. pfifo_fast is the first qdisc to support
the lockless bit that can be a child of a qdisc requiring locking. So
we add logic to clear the lock bit on initialization in these cases when
the qdisc graft operation occurs.

This also removes the logic used to pick the next band to dequeue from
and instead just checks a per priority array for packets from top priority
to lowest. This might need to be a bit more clever but seems to work
for now.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_api.c

@@ -955,6 +955,11 @@ skip:
 	} else {
 		const struct Qdisc_class_ops *cops = parent->ops->cl_ops;
 
+		/* Only support running class lockless if parent is lockless */
+		if (new && (new->flags & TCQ_F_NOLOCK) &&
+		    parent && !(parent->flags & TCQ_F_NOLOCK))
+			new->flags &= ~TCQ_F_NOLOCK;
+
 		err = -EOPNOTSUPP;
 		if (cops && cops->graft) {
 			unsigned long cl = cops->find(parent, classid);

net/sched/sch_generic.c

@@ -26,6 +26,7 @@
 #include <linux/list.h>
 #include <linux/slab.h>
 #include <linux/if_vlan.h>
+#include <linux/skb_array.h>
 #include <net/sch_generic.h>
 #include <net/pkt_sched.h>
 #include <net/dst.h>
@@ -578,93 +579,93 @@ static const u8 prio2band[TC_PRIO_MAX + 1] = {
 
 /*
  * Private data for a pfifo_fast scheduler containing:
- * 	- queues for the three band
- * 	- bitmap indicating which of the bands contain skbs
+ *	- rings for priority bands
  */
 struct pfifo_fast_priv {
-	u32 bitmap;
-	struct qdisc_skb_head q[PFIFO_FAST_BANDS];
+	struct skb_array q[PFIFO_FAST_BANDS];
 };
 
-/*
- * Convert a bitmap to the first band number where an skb is queued, where:
- * 	bitmap=0 means there are no skbs on any band.
- * 	bitmap=1 means there is an skb on band 0.
- *	bitmap=7 means there are skbs on all 3 bands, etc.
- */
-static const int bitmap2band[] = {-1, 0, 1, 0, 2, 0, 1, 0};
-
-static inline struct qdisc_skb_head *band2list(struct pfifo_fast_priv *priv,
-					     int band)
+static inline struct skb_array *band2list(struct pfifo_fast_priv *priv,
+					  int band)
 {
-	return priv->q + band;
+	return &priv->q[band];
 }
 
 static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc *qdisc,
 			      struct sk_buff **to_free)
 {
-	if (qdisc->q.qlen < qdisc_dev(qdisc)->tx_queue_len) {
-		int band = prio2band[skb->priority & TC_PRIO_MAX];
-		struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
-		struct qdisc_skb_head *list = band2list(priv, band);
-
-		priv->bitmap |= (1 << band);
-		qdisc->q.qlen++;
-		return __qdisc_enqueue_tail(skb, qdisc, list);
-	}
+	int band = prio2band[skb->priority & TC_PRIO_MAX];
+	struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
+	struct skb_array *q = band2list(priv, band);
+	int err;
 
-	return qdisc_drop(skb, qdisc, to_free);
+	err = skb_array_produce(q, skb);
+
+	if (unlikely(err))
+		return qdisc_drop_cpu(skb, qdisc, to_free);
+
+	qdisc_qstats_cpu_qlen_inc(qdisc);
+	qdisc_qstats_cpu_backlog_inc(qdisc, skb);
+	return NET_XMIT_SUCCESS;
 }
 
 static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc)
 {
 	struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
-	int band = bitmap2band[priv->bitmap];
-
-	if (likely(band >= 0)) {
-		struct qdisc_skb_head *qh = band2list(priv, band);
-		struct sk_buff *skb = __qdisc_dequeue_head(qh);
+	struct sk_buff *skb = NULL;
+	int band;
 
-		if (likely(skb != NULL)) {
-			qdisc_qstats_backlog_dec(qdisc, skb);
-			qdisc_bstats_update(qdisc, skb);
-		}
+	for (band = 0; band < PFIFO_FAST_BANDS && !skb; band++) {
+		struct skb_array *q = band2list(priv, band);
 
-		qdisc->q.qlen--;
-		if (qh->qlen == 0)
-			priv->bitmap &= ~(1 << band);
+		if (__skb_array_empty(q))
+			continue;
 
-		return skb;
+		skb = skb_array_consume_bh(q);
+	}
+	if (likely(skb)) {
+		qdisc_qstats_cpu_backlog_dec(qdisc, skb);
+		qdisc_bstats_cpu_update(qdisc, skb);
+		qdisc_qstats_cpu_qlen_dec(qdisc);
 	}
 
-	return NULL;
+	return skb;
 }
 
 static struct sk_buff *pfifo_fast_peek(struct Qdisc *qdisc)
 {
 	struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
-	int band = bitmap2band[priv->bitmap];
+	struct sk_buff *skb = NULL;
+	int band;
 
-	if (band >= 0) {
-		struct qdisc_skb_head *qh = band2list(priv, band);
+	for (band = 0; band < PFIFO_FAST_BANDS && !skb; band++) {
+		struct skb_array *q = band2list(priv, band);
 
-		return qh->head;
+		skb = __skb_array_peek(q);
 	}
 
-	return NULL;
+	return skb;
 }
 
 static void pfifo_fast_reset(struct Qdisc *qdisc)
 {
-	int prio;
+	int i, band;
 	struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
 
-	for (prio = 0; prio < PFIFO_FAST_BANDS; prio++)
-		__qdisc_reset_queue(band2list(priv, prio));
+	for (band = 0; band < PFIFO_FAST_BANDS; band++) {
+		struct skb_array *q = band2list(priv, band);
+		struct sk_buff *skb;
 
-	priv->bitmap = 0;
-	qdisc->qstats.backlog = 0;
-	qdisc->q.qlen = 0;
+		while ((skb = skb_array_consume_bh(q)) != NULL)
+			kfree_skb(skb);
+	}
+
+	for_each_possible_cpu(i) {
+		struct gnet_stats_queue *q = per_cpu_ptr(qdisc->cpu_qstats, i);
+
+		q->backlog = 0;
+		q->qlen = 0;
+	}
 }
 
 static int pfifo_fast_dump(struct Qdisc *qdisc, struct sk_buff *skb)
@@ -682,17 +683,48 @@ nla_put_failure:
 
 static int pfifo_fast_init(struct Qdisc *qdisc, struct nlattr *opt)
 {
-	int prio;
+	unsigned int qlen = qdisc_dev(qdisc)->tx_queue_len;
 	struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
+	int prio;
+
+	/* guard against zero length rings */
+	if (!qlen)
+		return -EINVAL;
 
-	for (prio = 0; prio < PFIFO_FAST_BANDS; prio++)
-		qdisc_skb_head_init(band2list(priv, prio));
+	for (prio = 0; prio < PFIFO_FAST_BANDS; prio++) {
+		struct skb_array *q = band2list(priv, prio);
+		int err;
+
+		err = skb_array_init(q, qlen, GFP_KERNEL);
+		if (err)
+			return -ENOMEM;
+	}
 
 	/* Can by-pass the queue discipline */
 	qdisc->flags |= TCQ_F_CAN_BYPASS;
 	return 0;
 }
 
+static void pfifo_fast_destroy(struct Qdisc *sch)
+{
+	struct pfifo_fast_priv *priv = qdisc_priv(sch);
+	int prio;
+
+	for (prio = 0; prio < PFIFO_FAST_BANDS; prio++) {
+		struct skb_array *q = band2list(priv, prio);
+
+		/* NULL ring is possible if destroy path is due to a failed
+		 * skb_array_init() in pfifo_fast_init() case.
+		 */
+		if (!&q->ring.queue)
+			continue;
+		/* Destroy ring but no need to kfree_skb because a call to
+		 * pfifo_fast_reset() has already done that work.
+		 */
+		ptr_ring_cleanup(&q->ring, NULL);
+	}
+}
+
 struct Qdisc_ops pfifo_fast_ops __read_mostly = {
 	.id		=	"pfifo_fast",
 	.priv_size	=	sizeof(struct pfifo_fast_priv),
@@ -700,9 +732,11 @@ struct Qdisc_ops pfifo_fast_ops __read_mostly = {
 	.dequeue	=	pfifo_fast_dequeue,
 	.peek		=	pfifo_fast_peek,
 	.init		=	pfifo_fast_init,
+	.destroy	=	pfifo_fast_destroy,
 	.reset		=	pfifo_fast_reset,
 	.dump		=	pfifo_fast_dump,
 	.owner		=	THIS_MODULE,
+	.static_flags	=	TCQ_F_NOLOCK | TCQ_F_CPUSTATS,
 };
 EXPORT_SYMBOL(pfifo_fast_ops);