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

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Date:   Tue,  7 Nov 2017 12:59:35 -0800
From:   Dave Taht <dave.taht@...il.com>
To:     netdev@...r.kernel.org
Cc:     Dave Taht <dave.taht@...il.com>
Subject: [PATCH net-next 2/3] netem: add uapi to express delay and jitter in nanosec

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@...il.com>
---
 include/uapi/linux/pkt_sched.h |  2 ++
 net/sched/sch_netem.c          | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 5002562..20cfd64 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -536,6 +536,8 @@ 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 443a75d..16c4813 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 +1028,14 @@ 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 (PSCHED_TICKS2NS(qopt.latency) != q->latency)
+		if (nla_put(skb, TCA_NETEM_LATENCY64, sizeof(q->latency),
+			    &q->latency))
+			goto nla_put_failure;
+	if (PSCHED_TICKS2NS(qopt.jitter) != q->jitter)
+		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