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Commit 0a9fe5c3 authored by Yousuk Seung's avatar Yousuk Seung Committed by David S. Miller
Browse files

netem: slotting with non-uniform distribution 



Extend slotting with support for non-uniform distributions. This is
similar to netem's non-uniform distribution delay feature.

Commit f043efeae2f1 ("netem: support delivering packets in delayed
time slots") added the slotting feature to approximate the behaviors
of media with packet aggregation but only supported a uniform
distribution for delays between transmission attempts. Tests with TCP
BBR with emulated wifi links with non-uniform distributions produced
more useful results.

Syntax:
   slot dist DISTRIBUTION DELAY JITTER [packets MAX_PACKETS] \
      [bytes MAX_BYTES]

The syntax and use of the distribution table is the same as in the
non-uniform distribution delay feature. A file DISTRIBUTION must be
present in TC_LIB_DIR (e.g. /usr/lib/tc) containing numbers scaled by
NETEM_DIST_SCALE. A random value x is selected from the table and it
takes DELAY + ( x * JITTER ) as delay. Correlation between values is not
supported.

Examples:
  Normal distribution delay with mean = 800us and stdev = 100us.
  > tc qdisc add dev eth0 root netem slot dist normal 800us 100us

  Optionally set the max slot size in bytes and/or packets.
  > tc qdisc add dev eth0 root netem slot dist normal 800us 100us \
    bytes 64k packets 42

Signed-off-by: default avatarYousuk Seung <ysseung@google.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 7861552c

include/uapi/linux/pkt_sched.h

+3 −0
Original line number Diff line number Diff line
@@ -539,6 +539,7 @@ enum { 
	TCA_NETEM_LATENCY64,

	TCA_NETEM_JITTER64,

	TCA_NETEM_SLOT,

	TCA_NETEM_SLOT_DIST,

	__TCA_NETEM_MAX,

};
@@ -581,6 +582,8 @@ struct tc_netem_slot { 
	__s64   max_delay;

	__s32   max_packets;

	__s32   max_bytes;

	__s64	dist_delay; /* nsec */

	__s64	dist_jitter; /* nsec */

};



enum {

net/sched/sch_netem.c

+49 −24
Original line number Diff line number Diff line
@@ -68,6 +68,11 @@ 
		 Fabio Ludovici <fabio.ludovici at yahoo.it>

*/



struct disttable {

	u32  size;

	s16 table[0];

};



struct netem_sched_data {

	/* internal t(ime)fifo qdisc uses t_root and sch->limit */

	struct rb_root t_root;
@@ -99,10 +104,7 @@ struct netem_sched_data { 
		u32 rho;

	} delay_cor, loss_cor, dup_cor, reorder_cor, corrupt_cor;



	struct disttable {

		u32  size;

		s16 table[0];

	} *delay_dist;

	struct disttable *delay_dist;



	enum  {

		CLG_RANDOM,
@@ -142,6 +144,7 @@ struct netem_sched_data { 
		s32 bytes_left;

	} slot;



	struct disttable *slot_dist;

};



/* Time stamp put into socket buffer control block
@@ -180,7 +183,7 @@ static u32 get_crandom(struct crndstate *state) 
	u64 value, rho;

	unsigned long answer;



	if (state->rho == 0)	/* no correlation */

	if (!state || state->rho == 0)	/* no correlation */

		return prandom_u32();



	value = prandom_u32();
@@ -601,10 +604,19 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch, 


static void get_slot_next(struct netem_sched_data *q, u64 now)

{

	q->slot.slot_next = now + q->slot_config.min_delay +

	s64 next_delay;



	if (!q->slot_dist)

		next_delay = q->slot_config.min_delay +

				(prandom_u32() *

				 (q->slot_config.max_delay -

				  q->slot_config.min_delay) >> 32);

	else

		next_delay = tabledist(q->slot_config.dist_delay,

				       (s32)(q->slot_config.dist_jitter),

				       NULL, q->slot_dist);



	q->slot.slot_next = now + next_delay;

	q->slot.packets_left = q->slot_config.max_packets;

	q->slot.bytes_left = q->slot_config.max_bytes;

}
@@ -721,9 +733,9 @@ static void dist_free(struct disttable *d) 
 * signed 16 bit values.

 */



static int get_dist_table(struct Qdisc *sch, const struct nlattr *attr)

static int get_dist_table(struct Qdisc *sch, struct disttable **tbl,

			  const struct nlattr *attr)

{

	struct netem_sched_data *q = qdisc_priv(sch);

	size_t n = nla_len(attr)/sizeof(__s16);

	const __s16 *data = nla_data(attr);

	spinlock_t *root_lock;
@@ -744,7 +756,7 @@ static int get_dist_table(struct Qdisc *sch, const struct nlattr *attr) 
	root_lock = qdisc_root_sleeping_lock(sch);



	spin_lock_bh(root_lock);

	swap(q->delay_dist, d);

	swap(*tbl, d);

	spin_unlock_bh(root_lock);



	dist_free(d);
@@ -762,7 +774,8 @@ static void get_slot(struct netem_sched_data *q, const struct nlattr *attr) 
		q->slot_config.max_bytes = INT_MAX;

	q->slot.packets_left = q->slot_config.max_packets;

	q->slot.bytes_left = q->slot_config.max_bytes;

	if (q->slot_config.min_delay | q->slot_config.max_delay)

	if (q->slot_config.min_delay | q->slot_config.max_delay |

	    q->slot_config.dist_jitter)

		q->slot.slot_next = ktime_get_ns();

	else

		q->slot.slot_next = 0;
@@ -926,16 +939,17 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt, 
	}



	if (tb[TCA_NETEM_DELAY_DIST]) {

		ret = get_dist_table(sch, tb[TCA_NETEM_DELAY_DIST]);

		if (ret) {

			/* recover clg and loss_model, in case of

			 * q->clg and q->loss_model were modified

			 * in get_loss_clg()

			 */

			q->clg = old_clg;

			q->loss_model = old_loss_model;

			return ret;

		ret = get_dist_table(sch, &q->delay_dist,

				     tb[TCA_NETEM_DELAY_DIST]);

		if (ret)

			goto get_table_failure;

	}



	if (tb[TCA_NETEM_SLOT_DIST]) {

		ret = get_dist_table(sch, &q->slot_dist,

				     tb[TCA_NETEM_SLOT_DIST]);

		if (ret)

			goto get_table_failure;

	}



	sch->limit = qopt->limit;
@@ -983,6 +997,15 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt, 
		get_slot(q, tb[TCA_NETEM_SLOT]);



	return ret;



get_table_failure:

	/* recover clg and loss_model, in case of

	 * q->clg and q->loss_model were modified

	 * in get_loss_clg()

	 */

	q->clg = old_clg;

	q->loss_model = old_loss_model;

	return ret;

}



static int netem_init(struct Qdisc *sch, struct nlattr *opt,
@@ -1011,6 +1034,7 @@ static void netem_destroy(struct Qdisc *sch) 
	if (q->qdisc)

		qdisc_destroy(q->qdisc);

	dist_free(q->delay_dist);

	dist_free(q->slot_dist);

}



static int dump_loss_model(const struct netem_sched_data *q,
@@ -1127,7 +1151,8 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff *skb) 
	if (dump_loss_model(q, skb) != 0)

		goto nla_put_failure;



	if (q->slot_config.min_delay | q->slot_config.max_delay) {

	if (q->slot_config.min_delay | q->slot_config.max_delay |

	    q->slot_config.dist_jitter) {

		slot = q->slot_config;

		if (slot.max_packets == INT_MAX)

			slot.max_packets = 0;