[PATCH v3 net-next 0/3] netem: add nsec scheduling and slot feature

[PATCH v3 net-next 0/3] netem: add nsec scheduling and slot feature

[Dave Taht]

This patch series converts netem away from the old "ticks" interface and
userspace API, and adds support for a new "slot" feature intended to
emulate bursty macs such as WiFi and LTE better.

Changes since v2:
Use u64 for packet_len_sched_time()
Use simpler max(time_to_send,q->slot.slot_next)

Changes since v1:
Always pass new nanosecond APIs to userspace

Dave Taht (3):
  netem: convert to qdisc_watchdog_schedule_ns
  netem: add uapi to express delay and jitter in nanoseconds
  netem: support delivering packets in delayed time slots

 include/uapi/linux/pkt_sched.h |  10 +++
 net/sched/sch_netem.c          | 140 ++++++++++++++++++++++++++++++++---------
 2 files changed, 121 insertions(+), 29 deletions(-)

-- 
2.7.4

[PATCH v3 net-next 1/3] netem: convert to qdisc_watchdog_schedule_ns

[Dave Taht]

Upgrade the internal netem scheduler to use nanoseconds rather than
ticks throughout.

Convert to and from the std "ticks" userspace api automatically,
while allowing for finer grained scheduling to take place.

Signed-off-by: Dave Taht <dave.taht@gmail.com>
---
 net/sched/sch_netem.c | 56 +++++++++++++++++++++++++--------------------------
 1 file changed, 28 insertions(+), 28 deletions(-)

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index db0228a..e64e0e0 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -77,8 +77,8 @@ struct netem_sched_data {
 
 	struct qdisc_watchdog watchdog;
 
-	psched_tdiff_t latency;
-	psched_tdiff_t jitter;
+	s64 latency;
+	s64 jitter;
 
 	u32 loss;
 	u32 ecn;
@@ -145,7 +145,7 @@ struct netem_sched_data {
  * we save skb->tstamp value in skb->cb[] before destroying it.
  */
 struct netem_skb_cb {
-	psched_time_t	time_to_send;
+	u64	        time_to_send;
 };
 
 static inline struct netem_skb_cb *netem_skb_cb(struct sk_buff *skb)
@@ -305,11 +305,11 @@ static bool loss_event(struct netem_sched_data *q)
  * std deviation sigma.  Uses table lookup to approximate the desired
  * distribution, and a uniformly-distributed pseudo-random source.
  */
-static psched_tdiff_t tabledist(psched_tdiff_t mu, psched_tdiff_t sigma,
-				struct crndstate *state,
-				const struct disttable *dist)
+static s64 tabledist(s64 mu, s64 sigma,
+		     struct crndstate *state,
+			 const struct disttable *dist)
 {
-	psched_tdiff_t x;
+	s64 x;
 	long t;
 	u32 rnd;
 
@@ -332,10 +332,10 @@ static psched_tdiff_t tabledist(psched_tdiff_t mu, psched_tdiff_t sigma,
 	return  x / NETEM_DIST_SCALE + (sigma / NETEM_DIST_SCALE) * t + mu;
 }
 
-static psched_time_t packet_len_2_sched_time(unsigned int len, struct netem_sched_data *q)
+static u64 packet_len_2_sched_time(unsigned int len,
+				   struct netem_sched_data *q)
 {
-	u64 ticks;
-
+	u64 offset;
 	len += q->packet_overhead;
 
 	if (q->cell_size) {
@@ -345,11 +345,9 @@ static psched_time_t packet_len_2_sched_time(unsigned int len, struct netem_sche
 			cells++;
 		len = cells * (q->cell_size + q->cell_overhead);
 	}
-
-	ticks = (u64)len * NSEC_PER_SEC;
-
-	do_div(ticks, q->rate);
-	return PSCHED_NS2TICKS(ticks);
+	offset = (u64)len * NSEC_PER_SEC;
+	do_div(offset, q->rate);
+	return offset;
 }
 
 static void tfifo_reset(struct Qdisc *sch)
@@ -369,7 +367,7 @@ static void tfifo_reset(struct Qdisc *sch)
 static void tfifo_enqueue(struct sk_buff *nskb, struct Qdisc *sch)
 {
 	struct netem_sched_data *q = qdisc_priv(sch);
-	psched_time_t tnext = netem_skb_cb(nskb)->time_to_send;
+	u64 tnext = netem_skb_cb(nskb)->time_to_send;
 	struct rb_node **p = &q->t_root.rb_node, *parent = NULL;
 
 	while (*p) {
@@ -515,13 +513,13 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	if (q->gap == 0 ||		/* not doing reordering */
 	    q->counter < q->gap - 1 ||	/* inside last reordering gap */
 	    q->reorder < get_crandom(&q->reorder_cor)) {
-		psched_time_t now;
-		psched_tdiff_t delay;
+		u64 now;
+		s64 delay;
 
 		delay = tabledist(q->latency, q->jitter,
 				  &q->delay_cor, q->delay_dist);
 
-		now = psched_get_time();
+		now = ktime_get_ns();
 
 		if (q->rate) {
 			struct netem_skb_cb *last = NULL;
@@ -547,7 +545,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 				 * from delay.
 				 */
 				delay -= last->time_to_send - now;
-				delay = max_t(psched_tdiff_t, 0, delay);
+				delay = max_t(s64, 0, delay);
 				now = last->time_to_send;
 			}
 
@@ -562,7 +560,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		 * Do re-ordering by putting one out of N packets at the front
 		 * of the queue.
 		 */
-		cb->time_to_send = psched_get_time();
+		cb->time_to_send = ktime_get_ns();
 		q->counter = 0;
 
 		netem_enqueue_skb_head(&sch->q, skb);
@@ -609,13 +607,13 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
 	}
 	p = rb_first(&q->t_root);
 	if (p) {
-		psched_time_t time_to_send;
+		u64 time_to_send;
 
 		skb = rb_to_skb(p);
 
 		/* if more time remaining? */
 		time_to_send = netem_skb_cb(skb)->time_to_send;
-		if (time_to_send <= psched_get_time()) {
+		if (time_to_send <= ktime_get_ns()) {
 			rb_erase(p, &q->t_root);
 
 			sch->q.qlen--;
@@ -659,7 +657,7 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
 			if (skb)
 				goto deliver;
 		}
-		qdisc_watchdog_schedule(&q->watchdog, time_to_send);
+		qdisc_watchdog_schedule_ns(&q->watchdog, time_to_send);
 	}
 
 	if (q->qdisc) {
@@ -888,8 +886,8 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt)
 
 	sch->limit = qopt->limit;
 
-	q->latency = qopt->latency;
-	q->jitter = qopt->jitter;
+	q->latency = PSCHED_TICKS2NS(qopt->latency);
+	q->jitter = PSCHED_TICKS2NS(qopt->jitter);
 	q->limit = qopt->limit;
 	q->gap = qopt->gap;
 	q->counter = 0;
@@ -1011,8 +1009,10 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff *skb)
 	struct tc_netem_corrupt corrupt;
 	struct tc_netem_rate rate;
 
-	qopt.latency = q->latency;
-	qopt.jitter = q->jitter;
+	qopt.latency = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->latency),
+			     UINT_MAX);
+	qopt.jitter = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->jitter),
+			    UINT_MAX);
 	qopt.limit = q->limit;
 	qopt.loss = q->loss;
 	qopt.gap = q->gap;
-- 
2.7.4

[PATCH v3 net-next 2/3] netem: add uapi to express delay and jitter in nanoseconds

[Dave Taht]

netem userspace has long relied on a horrible /proc/net/psched hack
to translate the current notion of "ticks" to nanoseconds.

Expressing latency and jitter instead, in well defined nanoseconds,
increases the dynamic range of emulated delays and jitter in netem.

It will also ease a transition where reducing a tick to nsec
equivalence would constrain the max delay in prior versions of
netem to only 4.3 seconds.

Signed-off-by: Dave Taht <dave.taht@gmail.com>
Suggested-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
---
 include/uapi/linux/pkt_sched.h |  2 ++
 net/sched/sch_netem.c          | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 6a2c5ea..8fe6d18 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -537,6 +537,8 @@ enum {
 	TCA_NETEM_ECN,
 	TCA_NETEM_RATE64,
 	TCA_NETEM_PAD,
+	TCA_NETEM_LATENCY64,
+	TCA_NETEM_JITTER64,
 	__TCA_NETEM_MAX,
 };
 
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index e64e0e0..47d6dec 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -819,6 +819,8 @@ static const struct nla_policy netem_policy[TCA_NETEM_MAX + 1] = {
 	[TCA_NETEM_LOSS]	= { .type = NLA_NESTED },
 	[TCA_NETEM_ECN]		= { .type = NLA_U32 },
 	[TCA_NETEM_RATE64]	= { .type = NLA_U64 },
+	[TCA_NETEM_LATENCY64]	= { .type = NLA_S64 },
+	[TCA_NETEM_JITTER64]	= { .type = NLA_S64 },
 };
 
 static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla,
@@ -916,6 +918,12 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt)
 		q->rate = max_t(u64, q->rate,
 				nla_get_u64(tb[TCA_NETEM_RATE64]));
 
+	if (tb[TCA_NETEM_LATENCY64])
+		q->latency = nla_get_s64(tb[TCA_NETEM_LATENCY64]);
+
+	if (tb[TCA_NETEM_JITTER64])
+		q->jitter = nla_get_s64(tb[TCA_NETEM_JITTER64]);
+
 	if (tb[TCA_NETEM_ECN])
 		q->ecn = nla_get_u32(tb[TCA_NETEM_ECN]);
 
@@ -1020,6 +1028,12 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff *skb)
 	if (nla_put(skb, TCA_OPTIONS, sizeof(qopt), &qopt))
 		goto nla_put_failure;
 
+	if (nla_put(skb, TCA_NETEM_LATENCY64, sizeof(q->latency), &q->latency))
+		goto nla_put_failure;
+
+	if (nla_put(skb, TCA_NETEM_JITTER64, sizeof(q->jitter), &q->jitter))
+		goto nla_put_failure;
+
 	cor.delay_corr = q->delay_cor.rho;
 	cor.loss_corr = q->loss_cor.rho;
 	cor.dup_corr = q->dup_cor.rho;
-- 
2.7.4

[PATCH v3 net-next 3/3] netem: support delivering packets in delayed time slots

[Dave Taht]

Slotting is a crude approximation of the behaviors of shared media such
as cable, wifi, and LTE, which gather up a bunch of packets within a
varying delay window and deliver them, relative to that, nearly all at
once.

It works within the existing loss, duplication, jitter and delay
parameters of netem. Some amount of inherent latency must be specified,
regardless.

The new "slot" parameter specifies a minimum and maximum delay between
transmission attempts.

The "bytes" and "packets" parameters can be used to limit the amount of
information transferred per slot.

Examples of use:

tc qdisc add dev eth0 root netem delay 200us \
         slot 800us 10ms bytes 64k packets 42

A more correct example, using stacked netem instances and a packet limit
to emulate a tail drop wifi queue with slots and variable packet
delivery, with a 200Mbit isochronous underlying rate, and 20ms path
delay:

tc qdisc add dev eth0 root handle 1: netem delay 20ms rate 200mbit \
         limit 10000
tc qdisc add dev eth0 parent 1:1 handle 10:1 netem delay 200us \
         slot 800us 10ms bytes 64k packets 42 limit 512

Signed-off-by: Dave Taht <dave.taht@gmail.com>
---
 include/uapi/linux/pkt_sched.h |  8 +++++
 net/sched/sch_netem.c          | 74 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 79 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 8fe6d18..af3cc2f 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -539,6 +539,7 @@ enum {
 	TCA_NETEM_PAD,
 	TCA_NETEM_LATENCY64,
 	TCA_NETEM_JITTER64,
+	TCA_NETEM_SLOT,
 	__TCA_NETEM_MAX,
 };
 
@@ -576,6 +577,13 @@ struct tc_netem_rate {
 	__s32	cell_overhead;
 };
 
+struct tc_netem_slot {
+	__s64   min_delay; /* nsec */
+	__s64   max_delay;
+	__s32   max_packets;
+	__s32   max_bytes;
+};
+
 enum {
 	NETEM_LOSS_UNSPEC,
 	NETEM_LOSS_GI,		/* General Intuitive - 4 state model */
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 47d6dec..b686e75 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -135,6 +135,13 @@ struct netem_sched_data {
 		u32 a5; /* p23 used only in 4-states */
 	} clg;
 
+	struct tc_netem_slot slot_config;
+	struct slotstate {
+		u64 slot_next;
+		s32 packets_left;
+		s32 bytes_left;
+	} slot;
+
 };
 
 /* Time stamp put into socket buffer control block
@@ -591,6 +598,20 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	return NET_XMIT_SUCCESS;
 }
 
+/* Delay the next round with a new future slot with a
+ * correct number of bytes and packets.
+ */
+
+static void get_slot_next(struct netem_sched_data *q, u64 now)
+{
+	q->slot.slot_next = now + q->slot_config.min_delay +
+		(prandom_u32() *
+			(q->slot_config.max_delay -
+				q->slot_config.min_delay) >> 32);
+	q->slot.packets_left = q->slot_config.max_packets;
+	q->slot.bytes_left = q->slot_config.max_bytes;
+}
+
 static struct sk_buff *netem_dequeue(struct Qdisc *sch)
 {
 	struct netem_sched_data *q = qdisc_priv(sch);
@@ -608,14 +629,17 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
 	p = rb_first(&q->t_root);
 	if (p) {
 		u64 time_to_send;
+		u64 now = ktime_get_ns();
 
 		skb = rb_to_skb(p);
 
 		/* if more time remaining? */
 		time_to_send = netem_skb_cb(skb)->time_to_send;
-		if (time_to_send <= ktime_get_ns()) {
-			rb_erase(p, &q->t_root);
+		if (q->slot.slot_next && q->slot.slot_next < time_to_send)
+			get_slot_next(q, now);
 
+		if (time_to_send <= now &&  q->slot.slot_next <= now) {
+			rb_erase(p, &q->t_root);
 			sch->q.qlen--;
 			qdisc_qstats_backlog_dec(sch, skb);
 			skb->next = NULL;
@@ -634,6 +658,14 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
 				skb->tstamp = 0;
 #endif
 
+			if (q->slot.slot_next) {
+				q->slot.packets_left--;
+				q->slot.bytes_left -= qdisc_pkt_len(skb);
+				if (q->slot.packets_left <= 0 ||
+				    q->slot.bytes_left <= 0)
+					get_slot_next(q, now);
+			}
+
 			if (q->qdisc) {
 				unsigned int pkt_len = qdisc_pkt_len(skb);
 				struct sk_buff *to_free = NULL;
@@ -657,7 +689,10 @@ static struct sk_buff *netem_dequeue(struct Qdisc *sch)
 			if (skb)
 				goto deliver;
 		}
-		qdisc_watchdog_schedule_ns(&q->watchdog, time_to_send);
+
+		qdisc_watchdog_schedule_ns(&q->watchdog,
+					   max(time_to_send,
+					       q->slot.slot_next));
 	}
 
 	if (q->qdisc) {
@@ -688,6 +723,7 @@ static void dist_free(struct disttable *d)
  * Distribution data is a variable size payload containing
  * signed 16 bit values.
  */
+
 static int get_dist_table(struct Qdisc *sch, const struct nlattr *attr)
 {
 	struct netem_sched_data *q = qdisc_priv(sch);
@@ -718,6 +754,23 @@ static int get_dist_table(struct Qdisc *sch, const struct nlattr *attr)
 	return 0;
 }
 
+static void get_slot(struct netem_sched_data *q, const struct nlattr *attr)
+{
+	const struct tc_netem_slot *c = nla_data(attr);
+
+	q->slot_config = *c;
+	if (q->slot_config.max_packets == 0)
+		q->slot_config.max_packets = INT_MAX;
+	if (q->slot_config.max_bytes == 0)
+		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)
+		q->slot.slot_next = ktime_get_ns();
+	else
+		q->slot.slot_next = 0;
+}
+
 static void get_correlation(struct netem_sched_data *q, const struct nlattr *attr)
 {
 	const struct tc_netem_corr *c = nla_data(attr);
@@ -821,6 +874,7 @@ static const struct nla_policy netem_policy[TCA_NETEM_MAX + 1] = {
 	[TCA_NETEM_RATE64]	= { .type = NLA_U64 },
 	[TCA_NETEM_LATENCY64]	= { .type = NLA_S64 },
 	[TCA_NETEM_JITTER64]	= { .type = NLA_S64 },
+	[TCA_NETEM_SLOT]	= { .len = sizeof(struct tc_netem_slot) },
 };
 
 static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla,
@@ -927,6 +981,9 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt)
 	if (tb[TCA_NETEM_ECN])
 		q->ecn = nla_get_u32(tb[TCA_NETEM_ECN]);
 
+	if (tb[TCA_NETEM_SLOT])
+		get_slot(q, tb[TCA_NETEM_SLOT]);
+
 	return ret;
 }
 
@@ -1016,6 +1073,7 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff *skb)
 	struct tc_netem_reorder reorder;
 	struct tc_netem_corrupt corrupt;
 	struct tc_netem_rate rate;
+	struct tc_netem_slot slot;
 
 	qopt.latency = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->latency),
 			     UINT_MAX);
@@ -1070,6 +1128,16 @@ 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) {
+		slot = q->slot_config;
+		if (slot.max_packets == INT_MAX)
+			slot.max_packets = 0;
+		if (slot.max_bytes == INT_MAX)
+			slot.max_bytes = 0;
+		if (nla_put(skb, TCA_NETEM_SLOT, sizeof(slot), &slot))
+			goto nla_put_failure;
+	}
+
 	return nla_nest_end(skb, nla);
 
 nla_put_failure:
-- 
2.7.4

Re: [PATCH v3 net-next 2/3] netem: add uapi to express delay and jitter in nanoseconds

[Stephen Hemminger]

On Wed,  8 Nov 2017 15:12:27 -0800
Dave Taht <dave.taht@gmail.com> wrote:

> --- a/net/sched/sch_netem.c
> +++ b/net/sched/sch_netem.c
> @@ -819,6 +819,8 @@ static const struct nla_policy netem_policy[TCA_NETEM_MAX + 1] = {
>  	[TCA_NETEM_LOSS]	= { .type = NLA_NESTED },
>  	[TCA_NETEM_ECN]		= { .type = NLA_U32 },
>  	[TCA_NETEM_RATE64]	= { .type = NLA_U64 },
> +	[TCA_NETEM_LATENCY64]	= { .type = NLA_S64 },
> +	[TCA_NETEM_JITTER64]	= { .type = NLA_S64 },
>  };
>  
>  static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla,
> @@ -916,6 +918,12 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt)
>  		q->rate = max_t(u64, q->rate,
>  				nla_get_u64(tb[TCA_NETEM_RATE64]));
>  
> +	if (tb[TCA_NETEM_LATENCY64])
> +		q->latency = nla_get_s64(tb[TCA_NETEM_LATENCY64]);
> +
> +	if (tb[TCA_NETEM_JITTER64])
> +		q->jitter = nla_get_s64(tb[TCA_NETEM_JITTER64]);
> +
>  	if (tb[TCA_NETEM_ECN])
>  		q->ecn = nla_get_u32(tb[TCA_NETEM_ECN]);
>  

Although some of the maths use signed 64 bit.
I think the API should be unsigned 64 bit.  Or do you want to allow
negative latency?

Re: [PATCH v3 net-next 2/3] netem: add uapi to express delay and jitter in nanoseconds

[Dave Taht]

On Wed, Nov 8, 2017 at 3:24 PM, Stephen Hemminger
<stephen@networkplumber.org> wrote:
> On Wed,  8 Nov 2017 15:12:27 -0800
> Dave Taht <dave.taht@gmail.com> wrote:
>
>> --- a/net/sched/sch_netem.c
>> +++ b/net/sched/sch_netem.c
>> @@ -819,6 +819,8 @@ static const struct nla_policy netem_policy[TCA_NETEM_MAX + 1] = {
>>       [TCA_NETEM_LOSS]        = { .type = NLA_NESTED },
>>       [TCA_NETEM_ECN]         = { .type = NLA_U32 },
>>       [TCA_NETEM_RATE64]      = { .type = NLA_U64 },
>> +     [TCA_NETEM_LATENCY64]   = { .type = NLA_S64 },
>> +     [TCA_NETEM_JITTER64]    = { .type = NLA_S64 },
>>  };
>>
>>  static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla,
>> @@ -916,6 +918,12 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt)
>>               q->rate = max_t(u64, q->rate,
>>                               nla_get_u64(tb[TCA_NETEM_RATE64]));
>>
>> +     if (tb[TCA_NETEM_LATENCY64])
>> +             q->latency = nla_get_s64(tb[TCA_NETEM_LATENCY64]);
>> +
>> +     if (tb[TCA_NETEM_JITTER64])
>> +             q->jitter = nla_get_s64(tb[TCA_NETEM_JITTER64]);
>> +
>>       if (tb[TCA_NETEM_ECN])
>>               q->ecn = nla_get_u32(tb[TCA_NETEM_ECN]);
>>
>
> Although some of the maths use signed 64 bit.
> I think the API should be unsigned 64 bit.  Or do you want to allow
> negative latency?

Personally I find things simpler to reason about when signed, and the
userspace side of the code (currently) offers the ability to generically
have signed time values for "other stuff".

The constrained range of 63 vs 64 bits we can debate in 272 years or so.

I'll let eric cast the tie vote.

-- 

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619

Re: [PATCH v3 net-next 2/3] netem: add uapi to express delay and jitter in nanoseconds

[Eric Dumazet]

On Wed, Nov 8, 2017 at 3:36 PM, Dave Taht <dave.taht@gmail.com> wrote:
> On Wed, Nov 8, 2017 at 3:24 PM, Stephen Hemminger
> <stephen@networkplumber.org> wrote:
>> On Wed,  8 Nov 2017 15:12:27 -0800
>> Dave Taht <dave.taht@gmail.com> wrote:
>>
>>> --- a/net/sched/sch_netem.c
>>> +++ b/net/sched/sch_netem.c
>>> @@ -819,6 +819,8 @@ static const struct nla_policy netem_policy[TCA_NETEM_MAX + 1] = {
>>>       [TCA_NETEM_LOSS]        = { .type = NLA_NESTED },
>>>       [TCA_NETEM_ECN]         = { .type = NLA_U32 },
>>>       [TCA_NETEM_RATE64]      = { .type = NLA_U64 },
>>> +     [TCA_NETEM_LATENCY64]   = { .type = NLA_S64 },
>>> +     [TCA_NETEM_JITTER64]    = { .type = NLA_S64 },
>>>  };
>>>
>>>  static int parse_attr(struct nlattr *tb[], int maxtype, struct nlattr *nla,
>>> @@ -916,6 +918,12 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt)
>>>               q->rate = max_t(u64, q->rate,
>>>                               nla_get_u64(tb[TCA_NETEM_RATE64]));
>>>
>>> +     if (tb[TCA_NETEM_LATENCY64])
>>> +             q->latency = nla_get_s64(tb[TCA_NETEM_LATENCY64]);
>>> +
>>> +     if (tb[TCA_NETEM_JITTER64])
>>> +             q->jitter = nla_get_s64(tb[TCA_NETEM_JITTER64]);
>>> +
>>>       if (tb[TCA_NETEM_ECN])
>>>               q->ecn = nla_get_u32(tb[TCA_NETEM_ECN]);
>>>
>>
>> Although some of the maths use signed 64 bit.
>> I think the API should be unsigned 64 bit.  Or do you want to allow
>> negative latency?
>
> Personally I find things simpler to reason about when signed, and the
> userspace side of the code (currently) offers the ability to generically
> have signed time values for "other stuff".
>
> The constrained range of 63 vs 64 bits we can debate in 272 years or so.

ktime_get_ns() returns number of nanosec in u64, since machine _boot_

So we wont have overflows, unless a linux host can stay up for more
than 500 years.

This seems unlikely.

Re: [PATCH v3 net-next 0/3] netem: add nsec scheduling and slot feature

[David Miller]

From: Dave Taht <dave.taht@gmail.com>
Date: Wed,  8 Nov 2017 15:12:25 -0800

> This patch series converts netem away from the old "ticks" interface and
> userspace API, and adds support for a new "slot" feature intended to
> emulate bursty macs such as WiFi and LTE better.
> 
> Changes since v2:
> Use u64 for packet_len_sched_time()
> Use simpler max(time_to_send,q->slot.slot_next)
> 
> Changes since v1:
> Always pass new nanosecond APIs to userspace

Series applied, thanks!