[Codel] [PATCH] Codel Take 4
Dave Täht
dave.taht at bufferbloat.net
Sat May 5 06:54:55 EDT 2012
scaled for 16 bits of precision and added cache
I've been testing with ethernet scaled down to 100Mbit so I can
get packet drop easily...
ethtool -K eth0 tso off
ethtool -K eth0 gso off
ethtool -s eth0 advertise 0x008
It's too early to benchmark but
one netperf has ping rtts ~8-11ms
vs 40 netperfs...
vs pfifo_fast, txqueue of 1000, ping rtt can hit 600ms. tcp_rr is <2 for
two streams..
With this
codel implementation, ping avg is good (2.5ms normall). tcp_rr is ~25 for
two streams...
Sharing is excellent vs a vs multiple streams...
100 packets transmitted, 97 received, 3% packet loss, time 99159ms
rtt min/avg/max/mdev = 2.321/25.837/86.491/8.383 ms
Feel free to substitute your own servers and ping targets
SERVER=huchra.bufferbloat.net
for i in `seq 1 10`
do
netperf -4 -l 120 -H $SERVER -t TCP_MAERTS &
netperf -4 -l 120 -H $SERVER -t TCP_STREAM &
netperf -6 -l 120 -H $SERVER -t TCP_MAERTS &
netperf -6 -l 120 -H $SERVER -t TCP_STREAM &
done
netperf -4 -l 60 -H $SERVER -t TCP_RR &
netperf -6 -l 60 -H $SERVER -t TCP_RR &
ping -c 100 8.8.8.8
---
include/linux/pkt_sched.h | 29 ++++
net/sched/Kconfig | 11 ++
net/sched/Makefile | 1 +
net/sched/sch_codel.c | 398 +++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 439 insertions(+)
create mode 100644 net/sched/sch_codel.c
diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
index 0d5b793..7d50687 100644
--- a/include/linux/pkt_sched.h
+++ b/include/linux/pkt_sched.h
@@ -633,4 +633,33 @@ struct tc_qfq_stats {
__u32 lmax;
};
+/* CODEL */
+
+enum {
+ TCA_CODEL_UNSPEC,
+ TCA_CODEL_PARMS,
+ TCA_CODEL_TARGET,
+ TCA_CODEL_LIMIT,
+ TCA_CODEL_MINBYTES,
+ TCA_CODEL_INTERVAL,
+ __TCA_CODEL_MAX
+};
+
+#define TCA_CODEL_MAX (__TCA_CODEL_MAX - 1)
+#define TC_CODEL_ECN 1
+
+struct tc_codel_qopt {
+ __u32 flags; /* flags (e.g. ecn) */
+ __u32 target; /* max delay, in us */
+ __u32 limit; /* queue limit in packets */
+ __u32 minbytes; /* MTU (usually) */
+ __u32 interval; /* Sliding min time window width (us) */
+};
+
+struct tc_codel_stats {
+ __u64 drops;
+ __u64 marks;
+};
+
+
#endif
diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index 2590e91..8106c42 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -250,6 +250,17 @@ config NET_SCH_QFQ
If unsure, say N.
+config NET_SCH_CODEL
+ tristate "Controlled Delay AQM (CODEL)"
+ help
+ Say Y here if you want to use the Controlled Delay (CODEL)
+ packet scheduling algorithm.
+
+ To compile this driver as a module, choose M here: the module
+ will be called sch_codel.
+
+ If unsure, say N.
+
config NET_SCH_INGRESS
tristate "Ingress Qdisc"
depends on NET_CLS_ACT
diff --git a/net/sched/Makefile b/net/sched/Makefile
index dc5889c..41130b5 100644
--- a/net/sched/Makefile
+++ b/net/sched/Makefile
@@ -36,6 +36,7 @@ obj-$(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..636f505
--- /dev/null
+++ b/net/sched/sch_codel.c
@@ -0,0 +1,398 @@
+/*
+ * 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.
+ *
+ * Codel, the COntrolled DELay Queueing discipline
+ * Based on ns2 simulation code presented by Kathie Nichols
+ * Authors: Dave Täht <d at taht.net>, Eric Dumazet <edumazet at google.com>
+ */
+
+#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 <linux/reciprocal_div.h>
+#include <net/pkt_sched.h>
+
+#define MS2TIME(a) (ns_to_ktime( (u64) a * NSEC_PER_MSEC))
+#define DEFAULT_CODEL_LIMIT 1000
+#define PRECALC_MAX 64
+
+/*
+ * Via patch found at:
+ * http://lkml.indiana.edu/hypermail/linux/kernel/0802.0/0659.html
+ * I don't know why this isn't in ktime.h as it seemed sane...
+*/
+
+/*
+ * ktime_compare - Compares two ktime_t variables
+ *
+ * Return val:
+ * lhs < rhs: < 0
+ * lhs == rhs: 0
+ * lhs > rhs: > 0
+ */
+
+#if (BITS_PER_LONG == 64) || defined(CONFIG_KTIME_SCALAR)
+static inline int ktime_compare(const ktime_t lhs, const ktime_t rhs)
+{
+ if (lhs.tv64 < rhs.tv64)
+ return -1;
+ if (lhs.tv64 > rhs.tv64)
+ return 1;
+ return 0;
+}
+#else
+static inline int ktime_compare(const ktime_t lhs, const ktime_t rhs)
+{
+ if (lhs.tv.sec < rhs.tv.sec)
+ return -1;
+ if (lhs.tv.sec > rhs.tv.sec)
+ return 1;
+ return lhs.tv.nsec - rhs.tv.nsec;
+}
+#endif
+
+/* 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;
+ ktime_t target;
+ /* time to declare above q->target (0 if below)*/
+ ktime_t first_above_time;
+ ktime_t drop_next; /* time to drop next packet */
+ unsigned long interval;
+ u32 precalc[PRECALC_MAX];
+};
+
+struct codel_skb_cb {
+ ktime_t enqueue_time;
+};
+
+static unsigned int state1;
+static unsigned int state2;
+static unsigned int state3;
+static unsigned int states;
+
+/*
+ * return interval/sqrt(x) with good precision
+ */
+
+static u32 calc(u64 interval, unsigned long x)
+{
+ /* scale for 16 bits precision */
+ while (x < (1UL << 30)) {
+ x <<= 2;
+ interval <<= 1;
+ }
+ do_div(interval, int_sqrt(x));
+ return (u32)interval;
+}
+
+static void codel_fill_cache(struct codel_sched_data *q) {
+ int i;
+
+ q->precalc[0] = q->interval;
+ for(i=2; i <= PRECALC_MAX; i++)
+ q->precalc[i-1] = calc(q->interval, i);
+}
+
+static struct codel_skb_cb *get_codel_cb(const struct sk_buff *skb)
+{
+ qdisc_cb_private_validate(skb, sizeof(struct codel_skb_cb));
+ return (struct codel_skb_cb *)qdisc_skb_cb(skb)->data;
+}
+
+static ktime_t get_enqueue_time(const struct sk_buff *skb)
+{
+ return get_codel_cb(skb)->enqueue_time;
+}
+
+static void set_enqueue_time(struct sk_buff *skb)
+{
+ get_codel_cb(skb)->enqueue_time = ktime_get();
+}
+
+/*
+ * The original control_law required floating point.
+ *
+ * return ktime_add_ns(t, q->interval / sqrt(q->count));
+ *
+ */
+
+static ktime_t control_law(const struct codel_sched_data *q, ktime_t t)
+{
+ if(unlikely(q->count > PRECALC_MAX))
+ return ktime_add_ns(t, calc(q->interval,q->count));
+ return ktime_add_ns(t, q->precalc[q->count - 1]);
+}
+
+/*
+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);
+ ktime_t sojourn_time;
+ bool drop = false;
+
+ if (!skb) {
+ q->first_above_time.tv64 = 0;
+ return false;
+ }
+ sojourn_time = ktime_sub(now, get_enqueue_time(skb));
+
+ if (ktime_compare(sojourn_time, q->target) < 0 ||
+ 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_ns(now, q->interval);
+ } else if (ktime_compare(now, q->first_above_time) >= 0) {
+ drop = true;
+ state1++;
+ }
+ }
+ 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;
+ unsigned int drop_count = 0;
+ bool drop;
+
+ if (!skb) {
+ q->dropping = false;
+ 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 = false;
+ } else if (ktime_compare(now, q->drop_next) >=0) {
+ state2++;
+ /* 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 (q->dropping &&
+ (ktime_compare(now, q->drop_next) >= 0)) {
+ codel_drop(skb, sch);
+ drop_count++;
+ q->count++;
+ skb = codel_dequeue_head(sch);
+ if (!should_drop(skb, sch, now)) {
+ /* leave dropping state */
+ q->dropping = false;
+ } else {
+ /* and schedule the next drop */
+ q->drop_next =
+ control_law(q, q->drop_next);
+ }
+ }
+ }
+ } else if (drop &&
+ ((ktime_compare(ktime_sub(now, q->drop_next),
+ ns_to_ktime(16 * q->interval)) < 0) ||
+ (ktime_compare(ktime_sub(now, q->first_above_time),
+ ns_to_ktime(2 * q->interval)) >= 0 ))) {
+ codel_drop(skb, sch);
+ drop_count++;
+ skb = codel_dequeue_head(sch);
+ drop = should_drop(skb, sch, now);
+ q->dropping = true;
+ state3++;
+ /*
+ * 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 (ktime_compare(ktime_sub(now, q->drop_next),
+ ns_to_ktime(16 * q->interval)) < 0) {
+ q->count = q->count > 1 ? q->count - 1 : 1;
+ } else {
+ q->count = 1;
+ }
+ q->drop_next = control_law(q, now);
+ }
+ if ((states++ % 64) == 0) {
+ pr_debug("s1: %u, s2: %u, s3: %u\n",
+ state1, state2, state3);
+ }
+ if (drop_count)
+ qdisc_tree_decrease_qlen(sch, drop_count);
+ 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);
+ 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;
+ pr_debug("minbytes: %u, target: %u, limit: %u, flags: %u\n",
+ ctl->minbytes, ctl->target, ctl->limit, ctl->flags);
+
+ if (opt->nla_len < nla_attr_size(sizeof(*ctl)))
+ return -EINVAL;
+ if (ctl->limit && (ctl->limit < 2 || ctl->limit > 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) {
+ u32 interval = min_t(u32, ~0U / NSEC_PER_USEC, ctl->interval);
+ q->interval = interval * NSEC_PER_USEC;
+ codel_fill_cache(q);
+ }
+ if (ctl->limit)
+ sch->limit = ctl->limit;
+ qlen = sch->q.qlen;
+ while (sch->q.qlen > ctl->limit)
+ qdisc_drop(qdisc_dequeue_head(sch), sch);
+ qdisc_tree_decrease_qlen(sch, qlen - sch->q.qlen);
+ q->drop_next.tv64 = q->first_above_time.tv64 = 0;
+ q->dropping = false;
+ 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);
+ /* It should be possible to run with no limit, actually */
+ sch->limit = DEFAULT_CODEL_LIMIT;
+ q->minbytes = psched_mtu(qdisc_dev(sch));
+ q->interval = 100 * NSEC_PER_MSEC;
+ q->drop_next.tv64 = q->first_above_time.tv64 = 0;
+ q->dropping = false; /* exit dropping state */
+ codel_fill_cache(q);
+// 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 = q->interval / NSEC_PER_USEC;
+ opt.limit = sch->limit;
+ opt.minbytes = q->minbytes;
+ opt.flags = q->flags;
+ if (nla_put(skb, TCA_OPTIONS, sizeof(opt), &opt))
+ goto nla_put_failure;
+ return skb->len;
+
+nla_put_failure:
+ 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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