samples/bpf/hbm_edt_kern.c

   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
  55 SEC("cgroup_skb/egress")
  56 int _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 }
 168 char _license[] SEC("license") = "GPL";