[Codel] [PATCH] Preliminary codel implementation

Dave Täht dave.taht at bufferbloat.net
Thu May 3 13:52:13 EDT 2012


---
 include/linux/pkt_sched.h |   29 +++++
 net/sched/Kconfig         |   11 ++
 net/sched/Makefile        |    1 +
 net/sched/sch_codel.c     |  296 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 337 insertions(+)
 create mode 100644 net/sched/sch_codel.c

diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
index 0d5b793..c21b720 100644
--- a/include/linux/pkt_sched.h
+++ b/include/linux/pkt_sched.h
@@ -633,4 +633,33 @@ struct tc_qfq_stats {
 	__u32 lmax;
 };
 
+/* CODEL */
+
+enum {
+	TCA_CODEL_UNSPEC,
+	TCA_CODEL_PARMS,
+	TCA_CODEL_TARGET,
+	TCA_CODEL_DEPTH,
+	TCA_CODEL_MINBYTES,
+	TCA_CODEL_INTERVAL,
+	__TCA_CODEL_MAX
+};
+
+#define TCA_CODEL_MAX	(__TCA_CODEL_MAX - 1)
+#define TC_CODEL_ECN 1
+
+struct tc_codel_qopt {
+        __u32 flags;	/* flags (e.g. ecn) */
+	__u32 target;	/* max delay, in us */
+        __u32 depth;	/* queue depth in packets */
+        __u32 minbytes;	/* MTU (usually) */
+        __u32 interval;	/* Sliding min time window width (us) */
+};
+
+struct tc_codel_stats {
+	__u64 drops;
+	__u64 marks;
+};
+
+
 #endif
diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index 2590e91..8106c42 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -250,6 +250,17 @@ config NET_SCH_QFQ
 
 	  If unsure, say N.
 
+config NET_SCH_CODEL
+	tristate "Controlled Delay AQM (CODEL)"
+	help
+	  Say Y here if you want to use the Controlled Delay (CODEL)
+	  packet scheduling algorithm.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called sch_codel.
+
+	  If unsure, say N.
+
 config NET_SCH_INGRESS
 	tristate "Ingress Qdisc"
 	depends on NET_CLS_ACT
diff --git a/net/sched/Makefile b/net/sched/Makefile
index dc5889c..41130b5 100644
--- a/net/sched/Makefile
+++ b/net/sched/Makefile
@@ -36,6 +36,7 @@ obj-$(CONFIG_NET_SCH_DRR)	+= sch_drr.o
 obj-$(CONFIG_NET_SCH_MQPRIO)	+= sch_mqprio.o
 obj-$(CONFIG_NET_SCH_CHOKE)	+= sch_choke.o
 obj-$(CONFIG_NET_SCH_QFQ)	+= sch_qfq.o
+obj-$(CONFIG_NET_SCH_CODEL)	+= sch_codel.o
 
 obj-$(CONFIG_NET_CLS_U32)	+= cls_u32.o
 obj-$(CONFIG_NET_CLS_ROUTE4)	+= cls_route.o
diff --git a/net/sched/sch_codel.c b/net/sched/sch_codel.c
new file mode 100644
index 0000000..159df47
--- /dev/null
+++ b/net/sched/sch_codel.c
@@ -0,0 +1,296 @@
+/*
+ * net/sched/sch_codel.c	A Codel implementation
+ *
+ *		This program is free software; you can redistribute it and/or
+ *		modify it under the terms of the GNU General Public License
+ *		as published by the Free Software Foundation; either version
+ *		2 of the License, or (at your option) any later version.
+ *
+ * Based on ns2 simulation code presented by Kathie Nichols
+ * Authors:	Dave Täht <d at taht.net>
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/ktime.h>
+#include <linux/skbuff.h>
+#include <net/pkt_sched.h>
+
+#define MS2TIME(a) (ns_to_ktime( (u64) a*1000000))
+#define DEFAULT_CODEL_DEPTH 1000
+
+/* Per-queue state (codel_queue_t instance variables) */
+
+struct codel_sched_data {
+	u32 flags;
+	u32 minbytes;
+	u32 count; /* packets dropped since we went into drop state */
+	bool dropping;	/* 1 if in drop state, might just add to flags */
+	ktime_t target;
+	ktime_t interval;
+        /* time to declare above q->target (0 if below)*/
+	ktime_t first_above_time;
+	ktime_t drop_next; /* time to drop next packet */
+};
+
+struct codel_skb_cb {
+	ktime_t enqueue_time;
+	char data[16];
+};
+
+static inline struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
+{
+	return (struct codel_skb_cb *)skb->cb;
+}
+
+static inline ktime_t get_enqueue_time(const struct sk_buff *skb) {
+	struct codel_skb_cb *cb = get_codel_cb(skb);
+	return cb->enqueue_time;
+}
+
+static inline ktime_t set_enqueue_time(struct sk_buff *skb, ktime_t t ) {
+	struct codel_skb_cb *cb = get_codel_cb(skb);
+	cb->enqueue_time = t;
+	return t;
+}
+
+static inline ktime_t control_law(const struct codel_sched_data *q, ktime_t t)
+{
+	t.tv64 = t.tv64 + q->interval.tv64 / int_sqrt(q->count);
+	return t;
+}
+
+/*
+static int codel_prob_mark(const struct codel_sched_data *q)
+{
+	return q->flags & TC_CODEL_ECN;
+}
+*/
+
+ /* wrappers for ultimate statistics collection */
+
+static int codel_drop(struct sk_buff *skb, struct Qdisc *sch) {
+	return qdisc_drop(skb,sch);
+}
+
+/*
+static int codel_queue_drop(struct Qdisc *sch) {
+	return qdisc_drop(skb,sch);
+}
+*/
+
+struct sk_buff *codel_dequeue_head(struct Qdisc *sch) {
+	return(qdisc_dequeue_head(sch));
+}
+
+bool should_drop(struct sk_buff *skb, struct Qdisc *sch, ktime_t now)
+{
+	struct codel_sched_data *q = qdisc_priv(sch);
+	bool drop = 0;
+	if (skb == NULL) {
+		q->first_above_time.tv64 = 0;
+	} else {
+		ktime_t sojourn_time = ktime_sub(now, get_enqueue_time(skb));
+		if (sojourn_time.tv64 < 
+		    q->target.tv64 || sch->qstats.backlog < q->minbytes) {
+/* went below so we’ll stay below for at least q->interval */
+			q->first_above_time.tv64 = 0;
+		} else {
+			if (q->first_above_time.tv64 == 0) {
+
+/* just went above from below. If we stay above
+ * for at least q->interval we’ll say it’s ok to drop 
+ */
+				q->first_above_time = 
+					ktime_add(now,q->interval);
+			} else if (now.tv64 >= q->first_above_time.tv64) {
+				drop = 1;
+			}
+		}
+	}
+	return drop;
+}
+
+static struct sk_buff *codel_dequeue(struct Qdisc *sch)
+{
+	struct codel_sched_data *q = qdisc_priv(sch);
+	struct sk_buff *skb = codel_dequeue_head(sch);
+	ktime_t now;
+	bool drop;
+	if (skb == NULL) {
+		q->dropping = 0;
+		q->first_above_time.tv64 = 0;
+		return skb;
+	}
+	now = ktime_get();
+	drop = should_drop(skb, sch, now);
+	if (q->dropping) {
+		if (drop) {
+/* sojourn time below target - leave dropping state */
+			q->dropping = 0;
+		} else if (now.tv64 >= q->drop_next.tv64) {
+/*
+ * It’s time for the next drop. Drop the current packet and dequeue the next. 
+ * The dequeue might take us out of dropping state. If not, schedule the 
+ * next drop. A large backlog might result in drop rates so high that the next
+ * drop should happen now, hence the ‘while’ loop.
+ */  
+			while (now.tv64 >= q->drop_next.tv64 && q->dropping) {
+				codel_drop(skb, sch);
+				q->count++;
+				skb = codel_dequeue_head(sch);
+				if (should_drop(skb,sch,now)) {
+/* leave dropping state */
+					q->dropping = 0;
+				} else {
+/* and schedule the next drop */
+					q->drop_next = 
+						control_law(q,q->drop_next);
+				}
+			}
+		} else if (drop &&
+			   ((now.tv64 - q->drop_next.tv64 < 
+				16 * q->interval.tv64) ||
+			    (now.tv64 - q->first_above_time.tv64 >= 
+			     2 * q->interval.tv64))) {
+			codel_drop(skb, sch);
+			skb = codel_dequeue_head(sch);
+			/* engage state machine */
+			drop = should_drop(skb,sch,now); 
+			q->dropping = 1;
+			
+/* if min went above target close to when we last went below it
+ * assume that the drop rate that controlled the queue on the
+ * last cycle is a good starting point to control it now.
+ */
+			if (now.tv64 - q->drop_next.tv64 < 
+				16 * q->interval.tv64) {
+				int c = q->count - 1;
+				q->count = c < 1 ? 1 : c;
+			} else {
+				q->count = 1;
+			}
+			q->drop_next = control_law(q,now);
+		}
+	}
+	return skb;
+}
+
+
+static int codel_enqueue(struct sk_buff *skb, struct Qdisc *sch)
+{
+	if (likely(skb_queue_len(&sch->q) < sch->limit)) {
+		set_enqueue_time(skb,ktime_get());
+		return qdisc_enqueue_tail(skb, sch);
+	}
+	return qdisc_reshape_fail(skb, sch);
+}
+
+static int codel_change(struct Qdisc *sch, struct nlattr *opt)
+{
+	struct codel_sched_data *q = qdisc_priv(sch);
+	struct tc_codel_qopt *ctl = nla_data(opt);
+	unsigned int qlen;
+
+	if (opt->nla_len < nla_attr_size(sizeof(*ctl)))
+		return -EINVAL;
+	if (ctl->depth && (ctl->depth < 2 || ctl->depth > 65536))
+		return -EINVAL;
+	if (ctl->minbytes && (ctl->minbytes < 64 || ctl->minbytes > 65536))
+		return -EINVAL;
+	sch_tree_lock(sch);
+	if (ctl->minbytes) q->minbytes = ctl->minbytes;
+	if (ctl->flags) q->flags = ctl->flags;
+	if (ctl->target) q->target = ns_to_ktime((u64) ctl->target * 1000); 
+	if (ctl->interval) q->interval = 
+			ns_to_ktime((u64) ctl->interval * 1000); 
+
+	/* something saner than this for depth is probably needed */
+
+	if (ctl->depth) sch->limit = ctl->depth;
+	qlen = sch->q.qlen;
+//	while (sch->q.qlen > ctl->depth)
+//		codel_drop(skb,sch);
+//	qdisc_tree_decrease_qlen(sch, qlen - sch->q.qlen); //?
+	q->drop_next.tv64 = q->first_above_time.tv64 = 0;
+	q->dropping = 0; /* exit dropping state */
+	sch_tree_unlock(sch);
+	return 0;
+}
+
+static int codel_init(struct Qdisc *sch, struct nlattr *opt)
+{
+	struct codel_sched_data *q = qdisc_priv(sch);
+	q->target = MS2TIME(5);
+	sch->limit =  DEFAULT_CODEL_DEPTH;
+	q->minbytes = 1500;
+	q->interval = MS2TIME(100);
+	if (opt) {
+		int err = codel_change(sch, opt);
+		if (err)
+			return err;
+	}
+
+/*	if (sch->limit >= 1)
+		sch->flags |= TCQ_F_CAN_BYPASS;
+	else
+		sch->flags &= ~TCQ_F_CAN_BYPASS;
+*/
+	return 0;
+}
+
+static int codel_dump(struct Qdisc *sch, struct sk_buff *skb)
+{
+	struct codel_sched_data *q = qdisc_priv(sch);
+	struct tc_codel_qopt opt;
+	opt.target = (u32) ktime_to_us(q->target);
+	opt.interval  = (u32) ktime_to_us(q->interval);
+	opt.depth  = sch->limit;
+	opt.flags  = q->flags;
+	NLA_PUT(skb, TCA_OPTIONS, sizeof(opt), &opt);
+	return skb->len;
+
+nla_put_failure:
+//	nlmsg_trim(skb, b);
+	return -1;
+}
+
+static void
+codel_reset(struct Qdisc *sch)
+{
+	struct sk_buff *skb;
+
+	while ((skb = codel_dequeue(sch)) != NULL)
+		kfree_skb(skb);
+}
+
+struct Qdisc_ops codel_qdisc_ops __read_mostly = {
+	.id		=	"codel",
+	.priv_size	=	sizeof(struct codel_sched_data),
+	.enqueue	=	codel_enqueue,
+	.dequeue	=	codel_dequeue,
+	.peek		=	qdisc_peek_head,
+/*	.drop		=	codel_queue_drop, */
+	.init		=	codel_init,
+	.reset		=	codel_reset,
+	.change		=	codel_change,
+	.dump		=	codel_dump,
+	.owner		=	THIS_MODULE,
+};
+EXPORT_SYMBOL(codel_qdisc_ops);
+
+static int __init codel_module_init(void)
+{
+        return register_qdisc(&codel_qdisc_ops);
+}
+static void __exit codel_module_exit(void)
+{
+        unregister_qdisc(&codel_qdisc_ops);
+}
+module_init(codel_module_init)
+module_exit(codel_module_exit)
+MODULE_LICENSE("GPL");
+
-- 
1.7.9.5




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