bpf: Add support for fq's EDT to HBM

Adds support for fq's Earliest Departure Time to HBM (Host Bandwidth
Manager). Includes a new BPF program supporting EDT, and also updates
corresponding programs.

It will drop packets with an EDT of more than 500us in the future
unless the packet belongs to a flow with less than 2 packets in flight.
This is done so each flow has at least 2 packets in flight, so they
will not starve, and also to help prevent delayed ACK timeouts.

It will also work with ECN enabled traffic, where the packets will be
CE marked if their EDT is more than 50us in the future.

The table below shows some performance numbers. The flows are back to
back RPCS. One server sending to another, either 2 or 4 flows.
One flow is a 10KB RPC, the rest are 1MB RPCs. When there are more
than one flow of a given RPC size, the numbers represent averages.

The rate limit applies to all flows (they are in the same cgroup).
Tests ending with "-edt" ran with the new BPF program supporting EDT.
Tests ending with "-hbt" ran on top HBT qdisc with the specified rate
(i.e. no HBM). The other tests ran with the HBM BPF program included
in the HBM patch-set.

EDT has limited value when using DCTCP, but it helps in many cases when
using Cubic. It usually achieves larger link utilization and lower
99% latencies for the 1MB RPCs.
HBM ends up queueing a lot of packets with its default parameter values,
reducing the goodput of the 10KB RPCs and increasing their latency. Also,
the RTTs seen by the flows are quite large.

                         Aggr              10K  10K  10K   1MB  1MB  1MB
         Limit           rate drops  RTT  rate  P90  P99  rate  P90  P99
Test      rate  Flows    Mbps   %     us  Mbps   us   us  Mbps   ms   ms
--------  ----  -----    ---- -----  ---  ---- ---- ----  ---- ---- ----
cubic       1G    2       904  0.02  108   257  511  539   647 13.4 24.5
cubic-edt   1G    2       982  0.01  156   239  656  967   743 14.0 17.2
dctcp       1G    2       977  0.00  105   324  408  744   653 14.5 15.9
dctcp-edt   1G    2       981  0.01  142   321  417  811   660 15.7 17.0
cubic-htb   1G    2       919  0.00 1825    40 2822 4140   879  9.7  9.9

cubic     200M    2       155  0.30  220    81  532  655    74  283  450
cubic-edt 200M    2       188  0.02  222    87 1035 1095   101   84   85
dctcp     200M    2       188  0.03  111    77  912  939   111   76  325
dctcp-edt 200M    2       188  0.03  217    74 1416 1738   114   76   79
cubic-htb 200M    2       188  0.00 5015     8 14ms 15ms   180   48   50

cubic       1G    4       952  0.03  110   165  516  546   262   38  154
cubic-edt   1G    4       973  0.01  190   111 1034 1314   287   65   79
dctcp       1G    4       951  0.00  103   180  617  905   257   37   38
dctcp-edt   1G    4       967  0.00  163   151  732 1126   272   43   55
cubic-htb   1G    4       914  0.00 3249    13  7ms  8ms   300   29   34

cubic       5G    4      4236  0.00  134   305  490  624  1310   10   17
cubic-edt   5G    4      4865  0.00  156   306  425  759  1520   10   16
dctcp       5G    4      4936  0.00  128   485  221  409  1484    7    9
dctcp-edt   5G    4      4924  0.00  148   390  392  623  1508   11   26

v1 -> v2: Incorporated Andrii's suggestions
v2 -> v3: Incorporated Yonghong's suggestions
v3 -> v4: Removed credit update that is not needed
Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

samples/bpf/Makefile

@@ -168,6 +168,7 @@ always += task_fd_query_kern.o
 always += xdp_sample_pkts_kern.o
 always += ibumad_kern.o
 always += hbm_out_kern.o
+always += hbm_edt_kern.o
 
 KBUILD_HOSTCFLAGS += -I$(objtree)/usr/include
 KBUILD_HOSTCFLAGS += -I$(srctree)/tools/lib/bpf/
@@ -272,6 +273,7 @@ $(src)/*.c: verify_target_bpf $(LIBBPF)
 $(obj)/tracex5_kern.o: $(obj)/syscall_nrs.h
 $(obj)/hbm_out_kern.o: $(src)/hbm.h $(src)/hbm_kern.h
 $(obj)/hbm.o: $(src)/hbm.h
+$(obj)/hbm_edt_kern.o: $(src)/hbm.h $(src)/hbm_kern.h
 
 # asm/sysreg.h - inline assembly used by it is incompatible with llvm.
 # But, there is no easy way to fix it, so just exclude it since it is

samples/bpf/do_hbm_test.sh

@@ -14,7 +14,7 @@ Usage() {
   echo "loads. The output is the goodput in Mbps (unless -D was used)."
   echo ""
   echo "USAGE: $name [out] [-b=<prog>|--bpf=<prog>] [-c=<cc>|--cc=<cc>]"
-  echo "             [-D] [-d=<delay>|--delay=<delay>] [--debug] [-E]"
+  echo "             [-D] [-d=<delay>|--delay=<delay>] [--debug] [-E] [--edt]"
   echo "             [-f=<#flows>|--flows=<#flows>] [-h] [-i=<id>|--id=<id >]"
   echo "             [-l] [-N] [--no_cn] [-p=<port>|--port=<port>] [-P]"
   echo "             [-q=<qdisc>] [-R] [-s=<server>|--server=<server]"
@@ -30,6 +30,7 @@ Usage() {
   echo "                      other detailed information. This information is"
   echo "                      test dependent (i.e. iperf3 or netperf)."
   echo "    -E                enable ECN (not required for dctcp)"
+  echo "    --edt             use fq's Earliest Departure Time (requires fq)"
   echo "    -f or --flows     number of concurrent flows (default=1)"
   echo "    -i or --id        cgroup id (an integer, default is 1)"
   echo "    -N                use netperf instead of iperf3"
@@ -130,13 +131,12 @@ processArgs () {
       details=1
       ;;
     -E)
-     ecn=1
+      ecn=1
+      ;;
+    --edt)
+      flags="$flags --edt"
+      qdisc="fq"
      ;;
-    # Support for upcomming fq Early Departure Time egress rate limiting
-    #--edt)
-    # prog="hbm_out_edt_kern.o"
-    # qdisc="fq"
-    # ;;
     -f=*|--flows=*)
       flows="${i#*=}"
       ;;
@@ -228,8 +228,8 @@ if [ "$netem" -ne "0" ] ; then
   tc qdisc del dev lo root > /dev/null 2>&1
   tc qdisc add dev lo root netem delay $netem\ms > /dev/null 2>&1
 elif [ "$qdisc" != "" ] ; then
-  tc qdisc del dev lo root > /dev/null 2>&1
-  tc qdisc add dev lo root $qdisc > /dev/null 2>&1
+  tc qdisc del dev eth0 root > /dev/null 2>&1
+  tc qdisc add dev eth0 root $qdisc > /dev/null 2>&1
 fi
 
 n=0
@@ -399,7 +399,9 @@ fi
 if [ "$netem" -ne "0" ] ; then
   tc qdisc del dev lo root > /dev/null 2>&1
 fi
-
+if [ "$qdisc" != "" ] ; then
+  tc qdisc del dev eth0 root > /dev/null 2>&1
+fi
 sleep 2
 
 hbmPid=`ps ax | grep "hbm " | grep --invert-match "grep" | awk '{ print $1 }'`

samples/bpf/hbm.c

@@ -62,6 +62,7 @@ bool loopback_flag;
 bool debugFlag;
 bool work_conserving_flag;
 bool no_cn_flag;
+bool edt_flag;
 
 static void Usage(void);
 static void read_trace_pipe2(void);
@@ -372,9 +373,14 @@ static int run_bpf_prog(char *prog, int cg_id)
 		fprintf(fout, "avg rtt:%d\n",
 			(int)(qstats.sum_rtt / (qstats.pkts_total + 1)));
 		// Average credit
-		fprintf(fout, "avg credit:%d\n",
-			(int)(qstats.sum_credit /
-			      (1500 * ((int)qstats.pkts_total) + 1)));
+		if (edt_flag)
+			fprintf(fout, "avg credit_ms:%.03f\n",
+				(qstats.sum_credit /
+				 (qstats.pkts_total + 1.0)) / 1000000.0);
+		else
+			fprintf(fout, "avg credit:%d\n",
+				(int)(qstats.sum_credit /
+				      (1500 * ((int)qstats.pkts_total ) + 1)));
 
 		// Return values stats
 		for (k = 0; k < RET_VAL_COUNT; k++) {
@@ -408,6 +414,7 @@ static void Usage(void)
 	       "  Where:\n"
 	       "    -o         indicates egress direction (default)\n"
 	       "    -d         print BPF trace debug buffer\n"
+	       "    --edt      use fq's Earliest Departure Time\n"
 	       "    -l         also limit flows using loopback\n"
 	       "    -n <#>     to create cgroup \"/hbm#\" and attach prog\n"
 	       "               Default is /hbm1\n"
@@ -433,6 +440,7 @@ int main(int argc, char **argv)
 	char *optstring = "iodln:r:st:wh";
 	struct option loptions[] = {
 		{"no_cn", 0, NULL, 1},
+		{"edt", 0, NULL, 2},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -441,6 +449,10 @@ int main(int argc, char **argv)
 		case 1:
 			no_cn_flag = true;
 			break;
+		case 2:
+			prog = "hbm_edt_kern.o";
+			edt_flag = true;
+			break;
 		case'o':
 			break;
 		case 'd':

samples/bpf/hbm_edt_kern.c

+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2019 Facebook
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ *
+ * Sample Host Bandwidth Manager (HBM) BPF program.
+ *
+ * A cgroup skb BPF egress program to limit cgroup output bandwidth.
+ * It uses a modified virtual token bucket queue to limit average
+ * egress bandwidth. The implementation uses credits instead of tokens.
+ * Negative credits imply that queueing would have happened (this is
+ * a virtual queue, so no queueing is done by it. However, queueing may
+ * occur at the actual qdisc (which is not used for rate limiting).
+ *
+ * This implementation uses 3 thresholds, one to start marking packets and
+ * the other two to drop packets:
+ *                                  CREDIT
+ *        - <--------------------------|------------------------> +
+ *              |    |          |      0
+ *              |  Large pkt    |
+ *              |  drop thresh  |
+ *   Small pkt drop             Mark threshold
+ *       thresh
+ *
+ * The effect of marking depends on the type of packet:
+ * a) If the packet is ECN enabled and it is a TCP packet, then the packet
+ *    is ECN marked.
+ * b) If the packet is a TCP packet, then we probabilistically call tcp_cwr
+ *    to reduce the congestion window. The current implementation uses a linear
+ *    distribution (0% probability at marking threshold, 100% probability
+ *    at drop threshold).
+ * c) If the packet is not a TCP packet, then it is dropped.
+ *
+ * If the credit is below the drop threshold, the packet is dropped. If it
+ * is a TCP packet, then it also calls tcp_cwr since packets dropped by
+ * by a cgroup skb BPF program do not automatically trigger a call to
+ * tcp_cwr in the current kernel code.
+ *
+ * This BPF program actually uses 2 drop thresholds, one threshold
+ * for larger packets (>= 120 bytes) and another for smaller packets. This
+ * protects smaller packets such as SYNs, ACKs, etc.
+ *
+ * The default bandwidth limit is set at 1Gbps but this can be changed by
+ * a user program through a shared BPF map. In addition, by default this BPF
+ * program does not limit connections using loopback. This behavior can be
+ * overwritten by the user program. There is also an option to calculate
+ * some statistics, such as percent of packets marked or dropped, which
+ * a user program, such as hbm, can access.
+ */
+
+#include "hbm_kern.h"
+
+SEC("cgroup_skb/egress")
+int _hbm_out_cg(struct __sk_buff *skb)
+{
+	long long delta = 0, delta_send;
+	unsigned long long curtime, sendtime;
+	struct hbm_queue_stats *qsp = NULL;
+	unsigned int queue_index = 0;
+	bool congestion_flag = false;
+	bool ecn_ce_flag = false;
+	struct hbm_pkt_info pkti = {};
+	struct hbm_vqueue *qdp;
+	bool drop_flag = false;
+	bool cwr_flag = false;
+	int len = skb->len;
+	int rv = ALLOW_PKT;
+
+	qsp = bpf_map_lookup_elem(&queue_stats, &queue_index);
+
+	// Check if we should ignore loopback traffic
+	if (qsp != NULL && !qsp->loopback && (skb->ifindex == 1))
+		return ALLOW_PKT;
+
+	hbm_get_pkt_info(skb, &pkti);
+
+	// We may want to account for the length of headers in len
+	// calculation, like ETH header + overhead, specially if it
+	// is a gso packet. But I am not doing it right now.
+
+	qdp = bpf_get_local_storage(&queue_state, 0);
+	if (!qdp)
+		return ALLOW_PKT;
+	if (qdp->lasttime == 0)
+		hbm_init_edt_vqueue(qdp, 1024);
+
+	curtime = bpf_ktime_get_ns();
+
+	// Begin critical section
+	bpf_spin_lock(&qdp->lock);
+	delta = qdp->lasttime - curtime;
+	// bound bursts to 100us
+	if (delta < -BURST_SIZE_NS) {
+		// negative delta is a credit that allows bursts
+		qdp->lasttime = curtime - BURST_SIZE_NS;
+		delta = -BURST_SIZE_NS;
+	}
+	sendtime = qdp->lasttime;
+	delta_send = BYTES_TO_NS(len, qdp->rate);
+	__sync_add_and_fetch(&(qdp->lasttime), delta_send);
+	bpf_spin_unlock(&qdp->lock);
+	// End critical section
+
+	// Set EDT of packet
+	skb->tstamp = sendtime;
+
+	// Check if we should update rate
+	if (qsp != NULL && (qsp->rate * 128) != qdp->rate)
+		qdp->rate = qsp->rate * 128;
+
+	// Set flags (drop, congestion, cwr)
+	// last packet will be sent in the future, bound latency
+	if (delta > DROP_THRESH_NS || (delta > LARGE_PKT_DROP_THRESH_NS &&
+				       len > LARGE_PKT_THRESH)) {
+		drop_flag = true;
+		if (pkti.is_tcp && pkti.ecn == 0)
+			cwr_flag = true;
+	} else if (delta > MARK_THRESH_NS) {
+		if (pkti.is_tcp)
+			congestion_flag = true;
+		else
+			drop_flag = true;
+	}
+
+	if (congestion_flag) {
+		if (bpf_skb_ecn_set_ce(skb)) {
+			ecn_ce_flag = true;
+		} else {
+			if (pkti.is_tcp) {
+				unsigned int rand = bpf_get_prandom_u32();
+
+				if (delta >= MARK_THRESH_NS +
+				    (rand % MARK_REGION_SIZE_NS)) {
+					// Do congestion control
+					cwr_flag = true;
+				}
+			} else if (len > LARGE_PKT_THRESH) {
+				// Problem if too many small packets?
+				drop_flag = true;
+				congestion_flag = false;
+			}
+		}
+	}
+
+	if (pkti.is_tcp && drop_flag && pkti.packets_out <= 1) {
+		drop_flag = false;
+		cwr_flag = true;
+		congestion_flag = false;
+	}
+
+	if (qsp != NULL && qsp->no_cn)
+			cwr_flag = false;
+
+	hbm_update_stats(qsp, len, curtime, congestion_flag, drop_flag,
+			 cwr_flag, ecn_ce_flag, &pkti, (int) delta);
+
+	if (drop_flag) {
+		__sync_add_and_fetch(&(qdp->lasttime), -delta_send);
+		rv = DROP_PKT;
+	}
+
+	if (cwr_flag)
+		rv |= CWR;
+	return rv;
+}
+char _license[] SEC("license") = "GPL";

samples/bpf/hbm_kern.h

@@ -29,6 +29,7 @@
 #define DROP_PKT	0
 #define ALLOW_PKT	1
 #define TCP_ECN_OK	1
+#define CWR		2
 
 #ifndef HBM_DEBUG  // Define HBM_DEBUG to enable debugging
 #undef bpf_printk
@@ -45,8 +46,18 @@
 #define MAX_CREDIT		(100 * MAX_BYTES_PER_PACKET)
 #define INIT_CREDIT		(INITIAL_CREDIT_PACKETS * MAX_BYTES_PER_PACKET)
 
+// Time base accounting for fq's EDT
+#define BURST_SIZE_NS		100000 // 100us
+#define MARK_THRESH_NS		50000 // 50us
+#define DROP_THRESH_NS		500000 // 500us
+// Reserve 20us of queuing for small packets (less than 120 bytes)
+#define LARGE_PKT_DROP_THRESH_NS (DROP_THRESH_NS - 20000)
+#define MARK_REGION_SIZE_NS	(LARGE_PKT_DROP_THRESH_NS - MARK_THRESH_NS)
+
 // rate in bytes per ns << 20
 #define CREDIT_PER_NS(delta, rate) ((((u64)(delta)) * (rate)) >> 20)
+#define BYTES_PER_NS(delta, rate) ((((u64)(delta)) * (rate)) >> 20)
+#define BYTES_TO_NS(bytes, rate) div64_u64(((u64)(bytes)) << 20, (u64)(rate))
 
 struct bpf_map_def SEC("maps") queue_state = {
 	.type = BPF_MAP_TYPE_CGROUP_STORAGE,
@@ -67,6 +78,7 @@ BPF_ANNOTATE_KV_PAIR(queue_stats, int, struct hbm_queue_stats);
 struct hbm_pkt_info {
 	int	cwnd;
 	int	rtt;
+	int	packets_out;
 	bool	is_ip;
 	bool	is_tcp;
 	short	ecn;
@@ -86,16 +98,20 @@ static int get_tcp_info(struct __sk_buff *skb, struct hbm_pkt_info *pkti)
 				if (tp) {
 					pkti->cwnd = tp->snd_cwnd;
 					pkti->rtt = tp->srtt_us >> 3;
+					pkti->packets_out = tp->packets_out;
 					return 0;
 				}
 			}
 		}
 	}
+	pkti->cwnd = 0;
+	pkti->rtt = 0;
+	pkti->packets_out = 0;
 	return 1;
 }
 
-static __always_inline void hbm_get_pkt_info(struct __sk_buff *skb,
-					     struct hbm_pkt_info *pkti)
+static void hbm_get_pkt_info(struct __sk_buff *skb,
+			     struct hbm_pkt_info *pkti)
 {
 	struct iphdr iph;
 	struct ipv6hdr *ip6h;
@@ -123,10 +139,22 @@ static __always_inline void hbm_get_pkt_info(struct __sk_buff *skb,
 
 static __always_inline void hbm_init_vqueue(struct hbm_vqueue *qdp, int rate)
 {
-		bpf_printk("Initializing queue_state, rate:%d\n", rate * 128);
-		qdp->lasttime = bpf_ktime_get_ns();
-		qdp->credit = INIT_CREDIT;
-		qdp->rate = rate * 128;
+	bpf_printk("Initializing queue_state, rate:%d\n", rate * 128);
+	qdp->lasttime = bpf_ktime_get_ns();
+	qdp->credit = INIT_CREDIT;
+	qdp->rate = rate * 128;
+}
+
+static __always_inline void hbm_init_edt_vqueue(struct hbm_vqueue *qdp,
+						int rate)
+{
+	unsigned long long curtime;
+
+	curtime = bpf_ktime_get_ns();
+	bpf_printk("Initializing queue_state, rate:%d\n", rate * 128);
+	qdp->lasttime = curtime - BURST_SIZE_NS;	// support initial burst
+	qdp->credit = 0;				// not used
+	qdp->rate = rate * 128;
 }
 
 static __always_inline void hbm_update_stats(struct hbm_queue_stats *qsp,