sch_cake: Add DiffServ handling

This adds support for DiffServ-based priority queueing to CAKE. If the
shaper is in use, each priority tier gets its own virtual clock, which
limits that tier's rate to a fraction of the overall shaped rate, to
discourage trying to game the priority mechanism.

CAKE defaults to a simple, three-tier mode that interprets most code points
as "best effort", but places CS1 traffic into a low-priority "bulk" tier
which is assigned 1/16 of the total rate, and a few code points indicating
latency-sensitive or control traffic (specifically TOS4, VA, EF, CS6, CS7)
into a "latency sensitive" high-priority tier, which is assigned 1/4 rate.
The other supported DiffServ modes are a 4-tier mode matching the 802.11e
precedence rules, as well as two 8-tier modes, one of which implements
strict precedence of the eight priority levels.

This commit also adds an optional DiffServ 'wash' mode, which will zero out
the DSCP fields of any packet passing through CAKE. While this can
technically be done with other mechanisms in the kernel, having the feature
available in CAKE significantly decreases configuration complexity; and the
implementation cost is low on top of the other DiffServ-handling code.

Filters and applications can set the skb->priority field to override the
DSCP-based classification into tiers. If TC_H_MAJ(skb->priority) matches
CAKE's qdisc handle, the minor number will be interpreted as a priority
tier if it is less than or equal to the number of configured priority
tiers.
Signed-off-by: NToke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/sched/sch_cake.c

@@ -296,6 +296,68 @@ static void cobalt_set_enqueue_time(struct sk_buff *skb,
 
 static u16 quantum_div[CAKE_QUEUES + 1] = {0};
 
+/* Diffserv lookup tables */
+
+static const u8 precedence[] = {
+	0, 0, 0, 0, 0, 0, 0, 0,
+	1, 1, 1, 1, 1, 1, 1, 1,
+	2, 2, 2, 2, 2, 2, 2, 2,
+	3, 3, 3, 3, 3, 3, 3, 3,
+	4, 4, 4, 4, 4, 4, 4, 4,
+	5, 5, 5, 5, 5, 5, 5, 5,
+	6, 6, 6, 6, 6, 6, 6, 6,
+	7, 7, 7, 7, 7, 7, 7, 7,
+};
+
+static const u8 diffserv8[] = {
+	2, 5, 1, 2, 4, 2, 2, 2,
+	0, 2, 1, 2, 1, 2, 1, 2,
+	5, 2, 4, 2, 4, 2, 4, 2,
+	3, 2, 3, 2, 3, 2, 3, 2,
+	6, 2, 3, 2, 3, 2, 3, 2,
+	6, 2, 2, 2, 6, 2, 6, 2,
+	7, 2, 2, 2, 2, 2, 2, 2,
+	7, 2, 2, 2, 2, 2, 2, 2,
+};
+
+static const u8 diffserv4[] = {
+	0, 2, 0, 0, 2, 0, 0, 0,
+	1, 0, 0, 0, 0, 0, 0, 0,
+	2, 0, 2, 0, 2, 0, 2, 0,
+	2, 0, 2, 0, 2, 0, 2, 0,
+	3, 0, 2, 0, 2, 0, 2, 0,
+	3, 0, 0, 0, 3, 0, 3, 0,
+	3, 0, 0, 0, 0, 0, 0, 0,
+	3, 0, 0, 0, 0, 0, 0, 0,
+};
+
+static const u8 diffserv3[] = {
+	0, 0, 0, 0, 2, 0, 0, 0,
+	1, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 2, 0, 2, 0,
+	2, 0, 0, 0, 0, 0, 0, 0,
+	2, 0, 0, 0, 0, 0, 0, 0,
+};
+
+static const u8 besteffort[] = {
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+	0, 0, 0, 0, 0, 0, 0, 0,
+};
+
+/* tin priority order for stats dumping */
+
+static const u8 normal_order[] = {0, 1, 2, 3, 4, 5, 6, 7};
+static const u8 bulk_order[] = {1, 0, 2, 3};
+
 #define REC_INV_SQRT_CACHE (16)
 static u32 cobalt_rec_inv_sqrt_cache[REC_INV_SQRT_CACHE] = {0};
 
@@ -1351,20 +1413,91 @@ static unsigned int cake_drop(struct Qdisc *sch, struct sk_buff **to_free)
 	return idx + (tin << 16);
 }
 
-static u32 cake_classify(struct Qdisc *sch, struct cake_tin_data *t,
+static void cake_wash_diffserv(struct sk_buff *skb)
+{
+	switch (skb->protocol) {
+	case htons(ETH_P_IP):
+		ipv4_change_dsfield(ip_hdr(skb), INET_ECN_MASK, 0);
+		break;
+	case htons(ETH_P_IPV6):
+		ipv6_change_dsfield(ipv6_hdr(skb), INET_ECN_MASK, 0);
+		break;
+	default:
+		break;
+	}
+}
+
+static u8 cake_handle_diffserv(struct sk_buff *skb, u16 wash)
+{
+	u8 dscp;
+
+	switch (skb->protocol) {
+	case htons(ETH_P_IP):
+		dscp = ipv4_get_dsfield(ip_hdr(skb)) >> 2;
+		if (wash && dscp)
+			ipv4_change_dsfield(ip_hdr(skb), INET_ECN_MASK, 0);
+		return dscp;
+
+	case htons(ETH_P_IPV6):
+		dscp = ipv6_get_dsfield(ipv6_hdr(skb)) >> 2;
+		if (wash && dscp)
+			ipv6_change_dsfield(ipv6_hdr(skb), INET_ECN_MASK, 0);
+		return dscp;
+
+	case htons(ETH_P_ARP):
+		return 0x38;  /* CS7 - Net Control */
+
+	default:
+		/* If there is no Diffserv field, treat as best-effort */
+		return 0;
+	}
+}
+
+static struct cake_tin_data *cake_select_tin(struct Qdisc *sch,
+					     struct sk_buff *skb)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	u32 tin;
+
+	if (TC_H_MAJ(skb->priority) == sch->handle &&
+	    TC_H_MIN(skb->priority) > 0 &&
+	    TC_H_MIN(skb->priority) <= q->tin_cnt) {
+		tin = TC_H_MIN(skb->priority) - 1;
+
+		if (q->rate_flags & CAKE_FLAG_WASH)
+			cake_wash_diffserv(skb);
+	} else if (q->tin_mode != CAKE_DIFFSERV_BESTEFFORT) {
+		/* extract the Diffserv Precedence field, if it exists */
+		/* and clear DSCP bits if washing */
+		tin = q->tin_index[cake_handle_diffserv(skb,
+				q->rate_flags & CAKE_FLAG_WASH)];
+		if (unlikely(tin >= q->tin_cnt))
+			tin = 0;
+	} else {
+		tin = 0;
+		if (q->rate_flags & CAKE_FLAG_WASH)
+			cake_wash_diffserv(skb);
+	}
+
+	return &q->tins[tin];
+}
+
+static u32 cake_classify(struct Qdisc *sch, struct cake_tin_data **t,
 			 struct sk_buff *skb, int flow_mode, int *qerr)
 {
 	struct cake_sched_data *q = qdisc_priv(sch);
 	struct tcf_proto *filter;
 	struct tcf_result res;
+	u32 flow = 0;
 	int result;
 
 	filter = rcu_dereference_bh(q->filter_list);
 	if (!filter)
-		return cake_hash(t, skb, flow_mode) + 1;
+		goto hash;
 
 	*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
 	result = tcf_classify(skb, filter, &res, false);
+
 	if (result >= 0) {
 #ifdef CONFIG_NET_CLS_ACT
 		switch (result) {
@@ -1378,9 +1511,11 @@ static u32 cake_classify(struct Qdisc *sch, struct cake_tin_data *t,
 		}
 #endif
 		if (TC_H_MIN(res.classid) <= CAKE_QUEUES)
-			return TC_H_MIN(res.classid);
+			flow = TC_H_MIN(res.classid);
 	}
-	return 0;
+hash:
+	*t = cake_select_tin(sch, skb);
+	return flow ?: cake_hash(*t, skb, flow_mode) + 1;
 }
 
 static void cake_reconfigure(struct Qdisc *sch);
@@ -1395,13 +1530,10 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 	ktime_t now = ktime_get();
 	struct cake_tin_data *b;
 	struct cake_flow *flow;
-	u32 idx, tin;
-
-	tin = 0;
-	b = &q->tins[tin];
+	u32 idx;
 
 	/* choose flow to insert into */
-	idx = cake_classify(sch, b, skb, q->flow_mode, &ret);
+	idx = cake_classify(sch, &b, skb, q->flow_mode, &ret);
 	if (idx == 0) {
 		if (ret & __NET_XMIT_BYPASS)
 			qdisc_qstats_drop(sch);
@@ -1917,18 +2049,275 @@ static void cake_set_rate(struct cake_tin_data *b, u64 rate, u32 mtu,
 	b->cparams.p_dec = 1 << 20; /* 1/4096 */
 }
 
-static void cake_reconfigure(struct Qdisc *sch)
+static int cake_config_besteffort(struct Qdisc *sch)
 {
 	struct cake_sched_data *q = qdisc_priv(sch);
 	struct cake_tin_data *b = &q->tins[0];
-	int c, ft = 0;
+	u32 mtu = psched_mtu(qdisc_dev(sch));
+	u64 rate = q->rate_bps;
 
 	q->tin_cnt = 1;
-	cake_set_rate(b, q->rate_bps, psched_mtu(qdisc_dev(sch)),
+
+	q->tin_index = besteffort;
+	q->tin_order = normal_order;
+
+	cake_set_rate(b, rate, mtu,
 		      us_to_ns(q->target), us_to_ns(q->interval));
 	b->tin_quantum_band = 65535;
 	b->tin_quantum_prio = 65535;
 
+	return 0;
+}
+
+static int cake_config_precedence(struct Qdisc *sch)
+{
+	/* convert high-level (user visible) parameters into internal format */
+	struct cake_sched_data *q = qdisc_priv(sch);
+	u32 mtu = psched_mtu(qdisc_dev(sch));
+	u64 rate = q->rate_bps;
+	u32 quantum1 = 256;
+	u32 quantum2 = 256;
+	u32 i;
+
+	q->tin_cnt = 8;
+	q->tin_index = precedence;
+	q->tin_order = normal_order;
+
+	for (i = 0; i < q->tin_cnt; i++) {
+		struct cake_tin_data *b = &q->tins[i];
+
+		cake_set_rate(b, rate, mtu, us_to_ns(q->target),
+			      us_to_ns(q->interval));
+
+		b->tin_quantum_prio = max_t(u16, 1U, quantum1);
+		b->tin_quantum_band = max_t(u16, 1U, quantum2);
+
+		/* calculate next class's parameters */
+		rate  *= 7;
+		rate >>= 3;
+
+		quantum1  *= 3;
+		quantum1 >>= 1;
+
+		quantum2  *= 7;
+		quantum2 >>= 3;
+	}
+
+	return 0;
+}
+
+/*	List of known Diffserv codepoints:
+ *
+ *	Least Effort (CS1)
+ *	Best Effort (CS0)
+ *	Max Reliability & LLT "Lo" (TOS1)
+ *	Max Throughput (TOS2)
+ *	Min Delay (TOS4)
+ *	LLT "La" (TOS5)
+ *	Assured Forwarding 1 (AF1x) - x3
+ *	Assured Forwarding 2 (AF2x) - x3
+ *	Assured Forwarding 3 (AF3x) - x3
+ *	Assured Forwarding 4 (AF4x) - x3
+ *	Precedence Class 2 (CS2)
+ *	Precedence Class 3 (CS3)
+ *	Precedence Class 4 (CS4)
+ *	Precedence Class 5 (CS5)
+ *	Precedence Class 6 (CS6)
+ *	Precedence Class 7 (CS7)
+ *	Voice Admit (VA)
+ *	Expedited Forwarding (EF)
+
+ *	Total 25 codepoints.
+ */
+
+/*	List of traffic classes in RFC 4594:
+ *		(roughly descending order of contended priority)
+ *		(roughly ascending order of uncontended throughput)
+ *
+ *	Network Control (CS6,CS7)      - routing traffic
+ *	Telephony (EF,VA)         - aka. VoIP streams
+ *	Signalling (CS5)               - VoIP setup
+ *	Multimedia Conferencing (AF4x) - aka. video calls
+ *	Realtime Interactive (CS4)     - eg. games
+ *	Multimedia Streaming (AF3x)    - eg. YouTube, NetFlix, Twitch
+ *	Broadcast Video (CS3)
+ *	Low Latency Data (AF2x,TOS4)      - eg. database
+ *	Ops, Admin, Management (CS2,TOS1) - eg. ssh
+ *	Standard Service (CS0 & unrecognised codepoints)
+ *	High Throughput Data (AF1x,TOS2)  - eg. web traffic
+ *	Low Priority Data (CS1)           - eg. BitTorrent
+
+ *	Total 12 traffic classes.
+ */
+
+static int cake_config_diffserv8(struct Qdisc *sch)
+{
+/*	Pruned list of traffic classes for typical applications:
+ *
+ *		Network Control          (CS6, CS7)
+ *		Minimum Latency          (EF, VA, CS5, CS4)
+ *		Interactive Shell        (CS2, TOS1)
+ *		Low Latency Transactions (AF2x, TOS4)
+ *		Video Streaming          (AF4x, AF3x, CS3)
+ *		Bog Standard             (CS0 etc.)
+ *		High Throughput          (AF1x, TOS2)
+ *		Background Traffic       (CS1)
+ *
+ *		Total 8 traffic classes.
+ */
+
+	struct cake_sched_data *q = qdisc_priv(sch);
+	u32 mtu = psched_mtu(qdisc_dev(sch));
+	u64 rate = q->rate_bps;
+	u32 quantum1 = 256;
+	u32 quantum2 = 256;
+	u32 i;
+
+	q->tin_cnt = 8;
+
+	/* codepoint to class mapping */
+	q->tin_index = diffserv8;
+	q->tin_order = normal_order;
+
+	/* class characteristics */
+	for (i = 0; i < q->tin_cnt; i++) {
+		struct cake_tin_data *b = &q->tins[i];
+
+		cake_set_rate(b, rate, mtu, us_to_ns(q->target),
+			      us_to_ns(q->interval));
+
+		b->tin_quantum_prio = max_t(u16, 1U, quantum1);
+		b->tin_quantum_band = max_t(u16, 1U, quantum2);
+
+		/* calculate next class's parameters */
+		rate  *= 7;
+		rate >>= 3;
+
+		quantum1  *= 3;
+		quantum1 >>= 1;
+
+		quantum2  *= 7;
+		quantum2 >>= 3;
+	}
+
+	return 0;
+}
+
+static int cake_config_diffserv4(struct Qdisc *sch)
+{
+/*  Further pruned list of traffic classes for four-class system:
+ *
+ *	    Latency Sensitive  (CS7, CS6, EF, VA, CS5, CS4)
+ *	    Streaming Media    (AF4x, AF3x, CS3, AF2x, TOS4, CS2, TOS1)
+ *	    Best Effort        (CS0, AF1x, TOS2, and those not specified)
+ *	    Background Traffic (CS1)
+ *
+ *		Total 4 traffic classes.
+ */
+
+	struct cake_sched_data *q = qdisc_priv(sch);
+	u32 mtu = psched_mtu(qdisc_dev(sch));
+	u64 rate = q->rate_bps;
+	u32 quantum = 1024;
+
+	q->tin_cnt = 4;
+
+	/* codepoint to class mapping */
+	q->tin_index = diffserv4;
+	q->tin_order = bulk_order;
+
+	/* class characteristics */
+	cake_set_rate(&q->tins[0], rate, mtu,
+		      us_to_ns(q->target), us_to_ns(q->interval));
+	cake_set_rate(&q->tins[1], rate >> 4, mtu,
+		      us_to_ns(q->target), us_to_ns(q->interval));
+	cake_set_rate(&q->tins[2], rate >> 1, mtu,
+		      us_to_ns(q->target), us_to_ns(q->interval));
+	cake_set_rate(&q->tins[3], rate >> 2, mtu,
+		      us_to_ns(q->target), us_to_ns(q->interval));
+
+	/* priority weights */
+	q->tins[0].tin_quantum_prio = quantum;
+	q->tins[1].tin_quantum_prio = quantum >> 4;
+	q->tins[2].tin_quantum_prio = quantum << 2;
+	q->tins[3].tin_quantum_prio = quantum << 4;
+
+	/* bandwidth-sharing weights */
+	q->tins[0].tin_quantum_band = quantum;
+	q->tins[1].tin_quantum_band = quantum >> 4;
+	q->tins[2].tin_quantum_band = quantum >> 1;
+	q->tins[3].tin_quantum_band = quantum >> 2;
+
+	return 0;
+}
+
+static int cake_config_diffserv3(struct Qdisc *sch)
+{
+/*  Simplified Diffserv structure with 3 tins.
+ *		Low Priority		(CS1)
+ *		Best Effort
+ *		Latency Sensitive	(TOS4, VA, EF, CS6, CS7)
+ */
+	struct cake_sched_data *q = qdisc_priv(sch);
+	u32 mtu = psched_mtu(qdisc_dev(sch));
+	u64 rate = q->rate_bps;
+	u32 quantum = 1024;
+
+	q->tin_cnt = 3;
+
+	/* codepoint to class mapping */
+	q->tin_index = diffserv3;
+	q->tin_order = bulk_order;
+
+	/* class characteristics */
+	cake_set_rate(&q->tins[0], rate, mtu,
+		      us_to_ns(q->target), us_to_ns(q->interval));
+	cake_set_rate(&q->tins[1], rate >> 4, mtu,
+		      us_to_ns(q->target), us_to_ns(q->interval));
+	cake_set_rate(&q->tins[2], rate >> 2, mtu,
+		      us_to_ns(q->target), us_to_ns(q->interval));
+
+	/* priority weights */
+	q->tins[0].tin_quantum_prio = quantum;
+	q->tins[1].tin_quantum_prio = quantum >> 4;
+	q->tins[2].tin_quantum_prio = quantum << 4;
+
+	/* bandwidth-sharing weights */
+	q->tins[0].tin_quantum_band = quantum;
+	q->tins[1].tin_quantum_band = quantum >> 4;
+	q->tins[2].tin_quantum_band = quantum >> 2;
+
+	return 0;
+}
+
+static void cake_reconfigure(struct Qdisc *sch)
+{
+	struct cake_sched_data *q = qdisc_priv(sch);
+	int c, ft;
+
+	switch (q->tin_mode) {
+	case CAKE_DIFFSERV_BESTEFFORT:
+		ft = cake_config_besteffort(sch);
+		break;
+
+	case CAKE_DIFFSERV_PRECEDENCE:
+		ft = cake_config_precedence(sch);
+		break;
+
+	case CAKE_DIFFSERV_DIFFSERV8:
+		ft = cake_config_diffserv8(sch);
+		break;
+
+	case CAKE_DIFFSERV_DIFFSERV4:
+		ft = cake_config_diffserv4(sch);
+		break;
+
+	case CAKE_DIFFSERV_DIFFSERV3:
+	default:
+		ft = cake_config_diffserv3(sch);
+		break;
+	}
+
 	for (c = q->tin_cnt; c < CAKE_MAX_TINS; c++) {
 		cake_clear_tin(sch, c);
 		q->tins[c].cparams.mtu_time = q->tins[ft].cparams.mtu_time;
@@ -1984,6 +2373,16 @@ static int cake_change(struct Qdisc *sch, struct nlattr *opt,
 	if (tb[TCA_CAKE_BASE_RATE64])
 		q->rate_bps = nla_get_u64(tb[TCA_CAKE_BASE_RATE64]);
 
+	if (tb[TCA_CAKE_DIFFSERV_MODE])
+		q->tin_mode = nla_get_u32(tb[TCA_CAKE_DIFFSERV_MODE]);
+
+	if (tb[TCA_CAKE_WASH]) {
+		if (!!nla_get_u32(tb[TCA_CAKE_WASH]))
+			q->rate_flags |= CAKE_FLAG_WASH;
+		else
+			q->rate_flags &= ~CAKE_FLAG_WASH;
+	}
+
 	if (tb[TCA_CAKE_FLOW_MODE])
 		q->flow_mode = ((q->flow_mode & CAKE_FLOW_NAT_FLAG) |
 				(nla_get_u32(tb[TCA_CAKE_FLOW_MODE]) &
@@ -2048,7 +2447,7 @@ static int cake_init(struct Qdisc *sch, struct nlattr *opt,
 	int i, j, err;
 
 	sch->limit = 10240;
-	q->tin_mode = CAKE_DIFFSERV_BESTEFFORT;
+	q->tin_mode = CAKE_DIFFSERV_DIFFSERV3;
 	q->flow_mode  = CAKE_FLOW_TRIPLE;
 
 	q->rate_bps = 0; /* unlimited by default */
@@ -2158,6 +2557,13 @@ static int cake_dump(struct Qdisc *sch, struct sk_buff *skb)
 			!!(q->flow_mode & CAKE_FLOW_NAT_FLAG)))
 		goto nla_put_failure;
 
+	if (nla_put_u32(skb, TCA_CAKE_DIFFSERV_MODE, q->tin_mode))
+		goto nla_put_failure;
+
+	if (nla_put_u32(skb, TCA_CAKE_WASH,
+			!!(q->rate_flags & CAKE_FLAG_WASH)))
+		goto nla_put_failure;
+
 	return nla_nest_end(skb, opts);
 
 nla_put_failure:
@@ -2211,7 +2617,7 @@ static int cake_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 	} while (0)
 
 	for (i = 0; i < q->tin_cnt; i++) {
-		struct cake_tin_data *b = &q->tins[i];
+		struct cake_tin_data *b = &q->tins[q->tin_order[i]];
 
 		ts = nla_nest_start(d->skb, i + 1);
 		if (!ts)
@@ -2310,7 +2716,8 @@ static int cake_dump_class_stats(struct Qdisc *sch, unsigned long cl,
 	u32 idx = cl - 1;
 
 	if (idx < CAKE_QUEUES * q->tin_cnt) {
-		const struct cake_tin_data *b = &q->tins[idx / CAKE_QUEUES];
+		const struct cake_tin_data *b = \
+			&q->tins[q->tin_order[idx / CAKE_QUEUES]];
 		const struct sk_buff *skb;
 
 		flow = &b->flows[idx % CAKE_QUEUES];
@@ -2382,7 +2789,7 @@ static void cake_walk(struct Qdisc *sch, struct qdisc_walker *arg)
 		return;
 
 	for (i = 0; i < q->tin_cnt; i++) {
-		struct cake_tin_data *b = &q->tins[i];
+		struct cake_tin_data *b = &q->tins[q->tin_order[i]];
 
 		for (j = 0; j < CAKE_QUEUES; j++) {
 			if (list_empty(&b->flows[j].flowchain) ||