net/sched/sch_cbs.c

   1 /*
   2  * net/sched/sch_cbs.c  Credit Based Shaper
   3  *
   4  *              This program is free software; you can redistribute it and/or
   5  *              modify it under the terms of the GNU General Public License
   6  *              as published by the Free Software Foundation; either version
   7  *              2 of the License, or (at your option) any later version.
   8  *
   9  * Authors:     Vinicius Costa Gomes <vinicius.gomes@intel.com>
  10  *
  11  */
  12
  13 /* Credit Based Shaper (CBS)
  14  * =========================
  15  *
  16  * This is a simple rate-limiting shaper aimed at TSN applications on
  17  * systems with known traffic workloads.
  18  *
  19  * Its algorithm is defined by the IEEE 802.1Q-2014 Specification,
  20  * Section 8.6.8.2, and explained in more detail in the Annex L of the
  21  * same specification.
  22  *
  23  * There are four tunables to be considered:
  24  *
  25  *      'idleslope': Idleslope is the rate of credits that is
  26  *      accumulated (in kilobits per second) when there is at least
  27  *      one packet waiting for transmission. Packets are transmitted
  28  *      when the current value of credits is equal or greater than
  29  *      zero. When there is no packet to be transmitted the amount of
  30  *      credits is set to zero. This is the main tunable of the CBS
  31  *      algorithm.
  32  *
  33  *      'sendslope':
  34  *      Sendslope is the rate of credits that is depleted (it should be a
  35  *      negative number of kilobits per second) when a transmission is
  36  *      ocurring. It can be calculated as follows, (IEEE 802.1Q-2014 Section
  37  *      8.6.8.2 item g):
  38  *
  39  *      sendslope = idleslope - port_transmit_rate
  40  *
  41  *      'hicredit': Hicredit defines the maximum amount of credits (in
  42  *      bytes) that can be accumulated. Hicredit depends on the
  43  *      characteristics of interfering traffic,
  44  *      'max_interference_size' is the maximum size of any burst of
  45  *      traffic that can delay the transmission of a frame that is
  46  *      available for transmission for this traffic class, (IEEE
  47  *      802.1Q-2014 Annex L, Equation L-3):
  48  *
  49  *      hicredit = max_interference_size * (idleslope / port_transmit_rate)
  50  *
  51  *      'locredit': Locredit is the minimum amount of credits that can
  52  *      be reached. It is a function of the traffic flowing through
  53  *      this qdisc (IEEE 802.1Q-2014 Annex L, Equation L-2):
  54  *
  55  *      locredit = max_frame_size * (sendslope / port_transmit_rate)
  56  */
  57
  58 #include <linux/module.h>
  59 #include <linux/types.h>
  60 #include <linux/kernel.h>
  61 #include <linux/string.h>
  62 #include <linux/errno.h>
  63 #include <linux/skbuff.h>
  64 #include <net/netlink.h>
  65 #include <net/sch_generic.h>
  66 #include <net/pkt_sched.h>
  67
  68 #define BYTES_PER_KBIT (1000LL / 8)
  69
  70 struct cbs_sched_data {
  71         bool offload;
  72         int queue;
  73         s64 port_rate; /* in bytes/s */
  74         s64 last; /* timestamp in ns */
  75         s64 credits; /* in bytes */
  76         s32 locredit; /* in bytes */
  77         s32 hicredit; /* in bytes */
  78         s64 sendslope; /* in bytes/s */
  79         s64 idleslope; /* in bytes/s */
  80         struct qdisc_watchdog watchdog;
  81         int (*enqueue)(struct sk_buff *skb, struct Qdisc *sch);
  82         struct sk_buff *(*dequeue)(struct Qdisc *sch);
  83 };
  84
  85 static int cbs_enqueue_offload(struct sk_buff *skb, struct Qdisc *sch)
  86 {
  87         return qdisc_enqueue_tail(skb, sch);
  88 }
  89
  90 static int cbs_enqueue_soft(struct sk_buff *skb, struct Qdisc *sch)
  91 {
  92         struct cbs_sched_data *q = qdisc_priv(sch);
  93
  94         if (sch->q.qlen == 0 && q->credits > 0) {
  95                 /* We need to stop accumulating credits when there's
  96                  * no enqueued packets and q->credits is positive.
  97                  */
  98                 q->credits = 0;
  99                 q->last = ktime_get_ns();
 100         }
 101
 102         return qdisc_enqueue_tail(skb, sch);
 103 }
 104
 105 static int cbs_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 106                        struct sk_buff **to_free)
 107 {
 108         struct cbs_sched_data *q = qdisc_priv(sch);
 109
 110         return q->enqueue(skb, sch);
 111 }
 112
 113 /* timediff is in ns, slope is in bytes/s */
 114 static s64 timediff_to_credits(s64 timediff, s64 slope)
 115 {
 116         return div64_s64(timediff * slope, NSEC_PER_SEC);
 117 }
 118
 119 static s64 delay_from_credits(s64 credits, s64 slope)
 120 {
 121         if (unlikely(slope == 0))
 122                 return S64_MAX;
 123
 124         return div64_s64(-credits * NSEC_PER_SEC, slope);
 125 }
 126
 127 static s64 credits_from_len(unsigned int len, s64 slope, s64 port_rate)
 128 {
 129         if (unlikely(port_rate == 0))
 130                 return S64_MAX;
 131
 132         return div64_s64(len * slope, port_rate);
 133 }
 134
 135 static struct sk_buff *cbs_dequeue_soft(struct Qdisc *sch)
 136 {
 137         struct cbs_sched_data *q = qdisc_priv(sch);
 138         s64 now = ktime_get_ns();
 139         struct sk_buff *skb;
 140         s64 credits;
 141         int len;
 142
 143         if (q->credits < 0) {
 144                 credits = timediff_to_credits(now - q->last, q->idleslope);
 145
 146                 credits = q->credits + credits;
 147                 q->credits = min_t(s64, credits, q->hicredit);
 148
 149                 if (q->credits < 0) {
 150                         s64 delay;
 151
 152                         delay = delay_from_credits(q->credits, q->idleslope);
 153                         qdisc_watchdog_schedule_ns(&q->watchdog, now + delay);
 154
 155                         q->last = now;
 156
 157                         return NULL;
 158                 }
 159         }
 160
 161         skb = qdisc_dequeue_head(sch);
 162         if (!skb)
 163                 return NULL;
 164
 165         len = qdisc_pkt_len(skb);
 166
 167         /* As sendslope is a negative number, this will decrease the
 168          * amount of q->credits.
 169          */
 170         credits = credits_from_len(len, q->sendslope, q->port_rate);
 171         credits += q->credits;
 172
 173         q->credits = max_t(s64, credits, q->locredit);
 174         q->last = now;
 175
 176         return skb;
 177 }
 178
 179 static struct sk_buff *cbs_dequeue_offload(struct Qdisc *sch)
 180 {
 181         return qdisc_dequeue_head(sch);
 182 }
 183
 184 static struct sk_buff *cbs_dequeue(struct Qdisc *sch)
 185 {
 186         struct cbs_sched_data *q = qdisc_priv(sch);
 187
 188         return q->dequeue(sch);
 189 }
 190
 191 static const struct nla_policy cbs_policy[TCA_CBS_MAX + 1] = {
 192         [TCA_CBS_PARMS] = { .len = sizeof(struct tc_cbs_qopt) },
 193 };
 194
 195 static void cbs_disable_offload(struct net_device *dev,
 196                                 struct cbs_sched_data *q)
 197 {
 198         struct tc_cbs_qopt_offload cbs = { };
 199         const struct net_device_ops *ops;
 200         int err;
 201
 202         if (!q->offload)
 203                 return;
 204
 205         q->enqueue = cbs_enqueue_soft;
 206         q->dequeue = cbs_dequeue_soft;
 207
 208         ops = dev->netdev_ops;
 209         if (!ops->ndo_setup_tc)
 210                 return;
 211
 212         cbs.queue = q->queue;
 213         cbs.enable = 0;
 214
 215         err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
 216         if (err < 0)
 217                 pr_warn("Couldn't disable CBS offload for queue %d\n",
 218                         cbs.queue);
 219 }
 220
 221 static int cbs_enable_offload(struct net_device *dev, struct cbs_sched_data *q,
 222                               const struct tc_cbs_qopt *opt)
 223 {
 224         const struct net_device_ops *ops = dev->netdev_ops;
 225         struct tc_cbs_qopt_offload cbs = { };
 226         int err;
 227
 228         if (!ops->ndo_setup_tc)
 229                 return -EOPNOTSUPP;
 230
 231         cbs.queue = q->queue;
 232
 233         cbs.enable = 1;
 234         cbs.hicredit = opt->hicredit;
 235         cbs.locredit = opt->locredit;
 236         cbs.idleslope = opt->idleslope;
 237         cbs.sendslope = opt->sendslope;
 238
 239         err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
 240         if (err < 0)
 241                 return err;
 242
 243         q->enqueue = cbs_enqueue_offload;
 244         q->dequeue = cbs_dequeue_offload;
 245
 246         return 0;
 247 }
 248
 249 static int cbs_change(struct Qdisc *sch, struct nlattr *opt)
 250 {
 251         struct cbs_sched_data *q = qdisc_priv(sch);
 252         struct net_device *dev = qdisc_dev(sch);
 253         struct nlattr *tb[TCA_CBS_MAX + 1];
 254         struct tc_cbs_qopt *qopt;
 255         int err;
 256
 257         err = nla_parse_nested(tb, TCA_CBS_MAX, opt, cbs_policy, NULL);
 258         if (err < 0)
 259                 return err;
 260
 261         if (!tb[TCA_CBS_PARMS])
 262                 return -EINVAL;
 263
 264         qopt = nla_data(tb[TCA_CBS_PARMS]);
 265
 266         if (!qopt->offload) {
 267                 struct ethtool_link_ksettings ecmd;
 268                 s64 link_speed;
 269
 270                 if (!__ethtool_get_link_ksettings(dev, &ecmd))
 271                         link_speed = ecmd.base.speed;
 272                 else
 273                         link_speed = SPEED_1000;
 274
 275                 q->port_rate = link_speed * 1000 * BYTES_PER_KBIT;
 276
 277                 cbs_disable_offload(dev, q);
 278         } else {
 279                 err = cbs_enable_offload(dev, q, qopt);
 280                 if (err < 0)
 281                         return err;
 282         }
 283
 284         /* Everything went OK, save the parameters used. */
 285         q->hicredit = qopt->hicredit;
 286         q->locredit = qopt->locredit;
 287         q->idleslope = qopt->idleslope * BYTES_PER_KBIT;
 288         q->sendslope = qopt->sendslope * BYTES_PER_KBIT;
 289         q->offload = qopt->offload;
 290
 291         return 0;
 292 }
 293
 294 static int cbs_init(struct Qdisc *sch, struct nlattr *opt)
 295 {
 296         struct cbs_sched_data *q = qdisc_priv(sch);
 297         struct net_device *dev = qdisc_dev(sch);
 298
 299         if (!opt)
 300                 return -EINVAL;
 301
 302         q->queue = sch->dev_queue - netdev_get_tx_queue(dev, 0);
 303
 304         q->enqueue = cbs_enqueue_soft;
 305         q->dequeue = cbs_dequeue_soft;
 306
 307         qdisc_watchdog_init(&q->watchdog, sch);
 308
 309         return cbs_change(sch, opt);
 310 }
 311
 312 static void cbs_destroy(struct Qdisc *sch)
 313 {
 314         struct cbs_sched_data *q = qdisc_priv(sch);
 315         struct net_device *dev = qdisc_dev(sch);
 316
 317         qdisc_watchdog_cancel(&q->watchdog);
 318
 319         cbs_disable_offload(dev, q);
 320 }
 321
 322 static int cbs_dump(struct Qdisc *sch, struct sk_buff *skb)
 323 {
 324         struct cbs_sched_data *q = qdisc_priv(sch);
 325         struct tc_cbs_qopt opt = { };
 326         struct nlattr *nest;
 327
 328         nest = nla_nest_start(skb, TCA_OPTIONS);
 329         if (!nest)
 330                 goto nla_put_failure;
 331
 332         opt.hicredit = q->hicredit;
 333         opt.locredit = q->locredit;
 334         opt.sendslope = div64_s64(q->sendslope, BYTES_PER_KBIT);
 335         opt.idleslope = div64_s64(q->idleslope, BYTES_PER_KBIT);
 336         opt.offload = q->offload;
 337
 338         if (nla_put(skb, TCA_CBS_PARMS, sizeof(opt), &opt))
 339                 goto nla_put_failure;
 340
 341         return nla_nest_end(skb, nest);
 342
 343 nla_put_failure:
 344         nla_nest_cancel(skb, nest);
 345         return -1;
 346 }
 347
 348 static struct Qdisc_ops cbs_qdisc_ops __read_mostly = {
 349         .id             =       "cbs",
 350         .priv_size      =       sizeof(struct cbs_sched_data),
 351         .enqueue        =       cbs_enqueue,
 352         .dequeue        =       cbs_dequeue,
 353         .peek           =       qdisc_peek_dequeued,
 354         .init           =       cbs_init,
 355         .reset          =       qdisc_reset_queue,
 356         .destroy        =       cbs_destroy,
 357         .change         =       cbs_change,
 358         .dump           =       cbs_dump,
 359         .owner          =       THIS_MODULE,
 360 };
 361
 362 static int __init cbs_module_init(void)
 363 {
 364         return register_qdisc(&cbs_qdisc_ops);
 365 }
 366
 367 static void __exit cbs_module_exit(void)
 368 {
 369         unregister_qdisc(&cbs_qdisc_ops);
 370 }
 371 module_init(cbs_module_init)
 372 module_exit(cbs_module_exit)
 373 MODULE_LICENSE("GPL");