hbm_edt_kern.c (5401B)
1// SPDX-License-Identifier: GPL-2.0 2/* Copyright (c) 2019 Facebook 3 * 4 * This program is free software; you can redistribute it and/or 5 * modify it under the terms of version 2 of the GNU General Public 6 * License as published by the Free Software Foundation. 7 * 8 * Sample Host Bandwidth Manager (HBM) BPF program. 9 * 10 * A cgroup skb BPF egress program to limit cgroup output bandwidth. 11 * It uses a modified virtual token bucket queue to limit average 12 * egress bandwidth. The implementation uses credits instead of tokens. 13 * Negative credits imply that queueing would have happened (this is 14 * a virtual queue, so no queueing is done by it. However, queueing may 15 * occur at the actual qdisc (which is not used for rate limiting). 16 * 17 * This implementation uses 3 thresholds, one to start marking packets and 18 * the other two to drop packets: 19 * CREDIT 20 * - <--------------------------|------------------------> + 21 * | | | 0 22 * | Large pkt | 23 * | drop thresh | 24 * Small pkt drop Mark threshold 25 * thresh 26 * 27 * The effect of marking depends on the type of packet: 28 * a) If the packet is ECN enabled and it is a TCP packet, then the packet 29 * is ECN marked. 30 * b) If the packet is a TCP packet, then we probabilistically call tcp_cwr 31 * to reduce the congestion window. The current implementation uses a linear 32 * distribution (0% probability at marking threshold, 100% probability 33 * at drop threshold). 34 * c) If the packet is not a TCP packet, then it is dropped. 35 * 36 * If the credit is below the drop threshold, the packet is dropped. If it 37 * is a TCP packet, then it also calls tcp_cwr since packets dropped by 38 * by a cgroup skb BPF program do not automatically trigger a call to 39 * tcp_cwr in the current kernel code. 40 * 41 * This BPF program actually uses 2 drop thresholds, one threshold 42 * for larger packets (>= 120 bytes) and another for smaller packets. This 43 * protects smaller packets such as SYNs, ACKs, etc. 44 * 45 * The default bandwidth limit is set at 1Gbps but this can be changed by 46 * a user program through a shared BPF map. In addition, by default this BPF 47 * program does not limit connections using loopback. This behavior can be 48 * overwritten by the user program. There is also an option to calculate 49 * some statistics, such as percent of packets marked or dropped, which 50 * a user program, such as hbm, can access. 51 */ 52 53#include "hbm_kern.h" 54 55SEC("cgroup_skb/egress") 56int _hbm_out_cg(struct __sk_buff *skb) 57{ 58 long long delta = 0, delta_send; 59 unsigned long long curtime, sendtime; 60 struct hbm_queue_stats *qsp = NULL; 61 unsigned int queue_index = 0; 62 bool congestion_flag = false; 63 bool ecn_ce_flag = false; 64 struct hbm_pkt_info pkti = {}; 65 struct hbm_vqueue *qdp; 66 bool drop_flag = false; 67 bool cwr_flag = false; 68 int len = skb->len; 69 int rv = ALLOW_PKT; 70 71 qsp = bpf_map_lookup_elem(&queue_stats, &queue_index); 72 73 // Check if we should ignore loopback traffic 74 if (qsp != NULL && !qsp->loopback && (skb->ifindex == 1)) 75 return ALLOW_PKT; 76 77 hbm_get_pkt_info(skb, &pkti); 78 79 // We may want to account for the length of headers in len 80 // calculation, like ETH header + overhead, specially if it 81 // is a gso packet. But I am not doing it right now. 82 83 qdp = bpf_get_local_storage(&queue_state, 0); 84 if (!qdp) 85 return ALLOW_PKT; 86 if (qdp->lasttime == 0) 87 hbm_init_edt_vqueue(qdp, 1024); 88 89 curtime = bpf_ktime_get_ns(); 90 91 // Begin critical section 92 bpf_spin_lock(&qdp->lock); 93 delta = qdp->lasttime - curtime; 94 // bound bursts to 100us 95 if (delta < -BURST_SIZE_NS) { 96 // negative delta is a credit that allows bursts 97 qdp->lasttime = curtime - BURST_SIZE_NS; 98 delta = -BURST_SIZE_NS; 99 } 100 sendtime = qdp->lasttime; 101 delta_send = BYTES_TO_NS(len, qdp->rate); 102 __sync_add_and_fetch(&(qdp->lasttime), delta_send); 103 bpf_spin_unlock(&qdp->lock); 104 // End critical section 105 106 // Set EDT of packet 107 skb->tstamp = sendtime; 108 109 // Check if we should update rate 110 if (qsp != NULL && (qsp->rate * 128) != qdp->rate) 111 qdp->rate = qsp->rate * 128; 112 113 // Set flags (drop, congestion, cwr) 114 // last packet will be sent in the future, bound latency 115 if (delta > DROP_THRESH_NS || (delta > LARGE_PKT_DROP_THRESH_NS && 116 len > LARGE_PKT_THRESH)) { 117 drop_flag = true; 118 if (pkti.is_tcp && pkti.ecn == 0) 119 cwr_flag = true; 120 } else if (delta > MARK_THRESH_NS) { 121 if (pkti.is_tcp) 122 congestion_flag = true; 123 else 124 drop_flag = true; 125 } 126 127 if (congestion_flag) { 128 if (bpf_skb_ecn_set_ce(skb)) { 129 ecn_ce_flag = true; 130 } else { 131 if (pkti.is_tcp) { 132 unsigned int rand = bpf_get_prandom_u32(); 133 134 if (delta >= MARK_THRESH_NS + 135 (rand % MARK_REGION_SIZE_NS)) { 136 // Do congestion control 137 cwr_flag = true; 138 } 139 } else if (len > LARGE_PKT_THRESH) { 140 // Problem if too many small packets? 141 drop_flag = true; 142 congestion_flag = false; 143 } 144 } 145 } 146 147 if (pkti.is_tcp && drop_flag && pkti.packets_out <= 1) { 148 drop_flag = false; 149 cwr_flag = true; 150 congestion_flag = false; 151 } 152 153 if (qsp != NULL && qsp->no_cn) 154 cwr_flag = false; 155 156 hbm_update_stats(qsp, len, curtime, congestion_flag, drop_flag, 157 cwr_flag, ecn_ce_flag, &pkti, (int) delta); 158 159 if (drop_flag) { 160 __sync_add_and_fetch(&(qdp->lasttime), -delta_send); 161 rv = DROP_PKT; 162 } 163 164 if (cwr_flag) 165 rv |= CWR; 166 return rv; 167} 168char _license[] SEC("license") = "GPL";