netdev - [PATCH v2] net: sched: Add support for packet bursting.

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Message-ID: <532A8EEC-59FD-42F2-8568-4C649677B4B0@itu.dk>
Date:   Mon, 28 Jun 2021 11:25:41 +0000
From:   Niclas Hedam <nhed@....dk>
To:     "stephen@...workplumber.org" <stephen@...workplumber.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH v2] net: sched: Add support for packet bursting.

>From 71843907bdb9cdc4e24358f0c16a8778f2762dc7 Mon Sep 17 00:00:00 2001
From: Niclas Hedam <nhed@....dk>
Date: Fri, 25 Jun 2021 13:37:18 +0200
Subject: [PATCH] net: sched: Add support for packet bursting.

This commit implements packet bursting in the NetEm scheduler.
This allows system administrators to hold back outgoing
packets and release them at a multiple of a time quantum.
This feature can be used to prevent timing attacks caused
by network latency.

Signed-off-by: Niclas Hedam <nhed@....dk>
---
v2: add enum at end of list (Cong Wang)
include/uapi/linux/pkt_sched.h |  2 ++
net/sched/sch_netem.c          | 24 +++++++++++++++++++++---
2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/pkt_sched.h b/include/uapi/linux/pkt_sched.h
index 79a699f106b1..1ba49f141dae 100644
--- a/include/uapi/linux/pkt_sched.h
+++ b/include/uapi/linux/pkt_sched.h
@@ -603,6 +603,7 @@ enum {
	TCA_NETEM_JITTER64,
	TCA_NETEM_SLOT,
	TCA_NETEM_SLOT_DIST,
+        TCA_NETEM_BURSTING,
	__TCA_NETEM_MAX,
};

@@ -615,6 +616,7 @@ struct tc_netem_qopt {
	__u32	gap;		/* re-ordering gap (0 for none) */
	__u32   duplicate;	/* random packet dup  (0=none ~0=100%) */
	__u32	jitter;		/* random jitter in latency (us) */
+	__u32	bursting;	/* send packets in bursts (us) */
};

struct tc_netem_corr {
diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 0c345e43a09a..52d796287b86 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -85,6 +85,7 @@ struct netem_sched_data {
	s64 latency;
	s64 jitter;

+	u32 bursting;
	u32 loss;
	u32 ecn;
	u32 limit;
@@ -467,7 +468,7 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
	/* If a delay is expected, orphan the skb. (orphaning usually takes
	 * place at TX completion time, so _before_ the link transit delay)
	 */
-	if (q->latency || q->jitter || q->rate)
+	if (q->latency || q->jitter || q->rate || q->bursting)
		skb_orphan_partial(skb);

	/*
@@ -527,8 +528,17 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
	qdisc_qstats_backlog_inc(sch, skb);

	cb = netem_skb_cb(skb);
-	if (q->gap == 0 ||		/* not doing reordering */
-	    q->counter < q->gap - 1 ||	/* inside last reordering gap */
+	if (q->bursting > 0) {
+		u64 now;
+
+		now = ktime_get_ns();
+
+		cb->time_to_send = now - (now % q->bursting) + q->bursting;
+
+		++q->counter;
+		tfifo_enqueue(skb, sch);
+	} else if (q->gap == 0 ||		/* not doing reordering */
+	    q->counter < q->gap - 1 ||		/* inside last reordering gap */
	    q->reorder < get_crandom(&q->reorder_cor)) {
		u64 now;
		s64 delay;
@@ -927,6 +937,7 @@ static const struct nla_policy netem_policy[TCA_NETEM_MAX + 1] = {
	[TCA_NETEM_ECN]		= { .type = NLA_U32 },
	[TCA_NETEM_RATE64]	= { .type = NLA_U64 },
	[TCA_NETEM_LATENCY64]	= { .type = NLA_S64 },
+	[TCA_NETEM_BURSTING]	= { .type = NLA_U64 },
	[TCA_NETEM_JITTER64]	= { .type = NLA_S64 },
	[TCA_NETEM_SLOT]	= { .len = sizeof(struct tc_netem_slot) },
};
@@ -1001,6 +1012,7 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,

	q->latency = PSCHED_TICKS2NS(qopt->latency);
	q->jitter = PSCHED_TICKS2NS(qopt->jitter);
+	q->bursting = PSCHED_TICKS2NS(qopt->bursting);
	q->limit = qopt->limit;
	q->gap = qopt->gap;
	q->counter = 0;
@@ -1032,6 +1044,9 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
	if (tb[TCA_NETEM_LATENCY64])
		q->latency = nla_get_s64(tb[TCA_NETEM_LATENCY64]);

+	if (tb[TCA_NETEM_BURSTING])
+		q->bursting = nla_get_u64(tb[TCA_NETEM_BURSTING]);
+
	if (tb[TCA_NETEM_JITTER64])
		q->jitter = nla_get_s64(tb[TCA_NETEM_JITTER64]);

@@ -1150,6 +1165,9 @@ static int netem_dump(struct Qdisc *sch, struct sk_buff *skb)
			     UINT_MAX);
	qopt.jitter = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->jitter),
			    UINT_MAX);
+	qopt.bursting = min_t(psched_tdiff_t, PSCHED_NS2TICKS(q->bursting),
+			    UINT_MAX);
+
	qopt.limit = q->limit;
	qopt.loss = q->loss;
	qopt.gap = q->gap;
--
2.25.1