net/sched/sch_cbs.c

0001 // SPDX-License-Identifier: GPL-2.0-or-later
0002 /*
0003  * net/sched/sch_cbs.c  Credit Based Shaper
0004  *
0005  * Authors: Vinicius Costa Gomes <vinicius.gomes@intel.com>
0006  */
0007
0008 /* Credit Based Shaper (CBS)
0009  * =========================
0010  *
0011  * This is a simple rate-limiting shaper aimed at TSN applications on
0012  * systems with known traffic workloads.
0013  *
0014  * Its algorithm is defined by the IEEE 802.1Q-2014 Specification,
0015  * Section 8.6.8.2, and explained in more detail in the Annex L of the
0016  * same specification.
0017  *
0018  * There are four tunables to be considered:
0019  *
0020  *  'idleslope': Idleslope is the rate of credits that is
0021  *  accumulated (in kilobits per second) when there is at least
0022  *  one packet waiting for transmission. Packets are transmitted
0023  *  when the current value of credits is equal or greater than
0024  *  zero. When there is no packet to be transmitted the amount of
0025  *  credits is set to zero. This is the main tunable of the CBS
0026  *  algorithm.
0027  *
0028  *  'sendslope':
0029  *  Sendslope is the rate of credits that is depleted (it should be a
0030  *  negative number of kilobits per second) when a transmission is
0031  *  ocurring. It can be calculated as follows, (IEEE 802.1Q-2014 Section
0032  *  8.6.8.2 item g):
0033  *
0034  *  sendslope = idleslope - port_transmit_rate
0035  *
0036  *  'hicredit': Hicredit defines the maximum amount of credits (in
0037  *  bytes) that can be accumulated. Hicredit depends on the
0038  *  characteristics of interfering traffic,
0039  *  'max_interference_size' is the maximum size of any burst of
0040  *  traffic that can delay the transmission of a frame that is
0041  *  available for transmission for this traffic class, (IEEE
0042  *  802.1Q-2014 Annex L, Equation L-3):
0043  *
0044  *  hicredit = max_interference_size * (idleslope / port_transmit_rate)
0045  *
0046  *  'locredit': Locredit is the minimum amount of credits that can
0047  *  be reached. It is a function of the traffic flowing through
0048  *  this qdisc (IEEE 802.1Q-2014 Annex L, Equation L-2):
0049  *
0050  *  locredit = max_frame_size * (sendslope / port_transmit_rate)
0051  */
0052
0053 #include <linux/ethtool.h>
0054 #include <linux/module.h>
0055 #include <linux/types.h>
0056 #include <linux/kernel.h>
0057 #include <linux/string.h>
0058 #include <linux/errno.h>
0059 #include <linux/skbuff.h>
0060 #include <net/netevent.h>
0061 #include <net/netlink.h>
0062 #include <net/sch_generic.h>
0063 #include <net/pkt_sched.h>
0064
0065 static LIST_HEAD(cbs_list);
0066 static DEFINE_SPINLOCK(cbs_list_lock);
0067
0068 #define BYTES_PER_KBIT (1000LL / 8)
0069
0070 struct cbs_sched_data {
0071     bool offload;
0072     int queue;
0073     atomic64_t port_rate; /* in bytes/s */
0074     s64 last; /* timestamp in ns */
0075     s64 credits; /* in bytes */
0076     s32 locredit; /* in bytes */
0077     s32 hicredit; /* in bytes */
0078     s64 sendslope; /* in bytes/s */
0079     s64 idleslope; /* in bytes/s */
0080     struct qdisc_watchdog watchdog;
0081     int (*enqueue)(struct sk_buff *skb, struct Qdisc *sch,
0082                struct sk_buff **to_free);
0083     struct sk_buff *(*dequeue)(struct Qdisc *sch);
0084     struct Qdisc *qdisc;
0085     struct list_head cbs_list;
0086 };
0087
0088 static int cbs_child_enqueue(struct sk_buff *skb, struct Qdisc *sch,
0089                  struct Qdisc *child,
0090                  struct sk_buff **to_free)
0091 {
0092     unsigned int len = qdisc_pkt_len(skb);
0093     int err;
0094
0095     err = child->ops->enqueue(skb, child, to_free);
0096     if (err != NET_XMIT_SUCCESS)
0097         return err;
0098
0099     sch->qstats.backlog += len;
0100     sch->q.qlen++;
0101
0102     return NET_XMIT_SUCCESS;
0103 }
0104
0105 static int cbs_enqueue_offload(struct sk_buff *skb, struct Qdisc *sch,
0106                    struct sk_buff **to_free)
0107 {
0108     struct cbs_sched_data *q = qdisc_priv(sch);
0109     struct Qdisc *qdisc = q->qdisc;
0110
0111     return cbs_child_enqueue(skb, sch, qdisc, to_free);
0112 }
0113
0114 static int cbs_enqueue_soft(struct sk_buff *skb, struct Qdisc *sch,
0115                 struct sk_buff **to_free)
0116 {
0117     struct cbs_sched_data *q = qdisc_priv(sch);
0118     struct Qdisc *qdisc = q->qdisc;
0119
0120     if (sch->q.qlen == 0 && q->credits > 0) {
0121         /* We need to stop accumulating credits when there's
0122          * no enqueued packets and q->credits is positive.
0123          */
0124         q->credits = 0;
0125         q->last = ktime_get_ns();
0126     }
0127
0128     return cbs_child_enqueue(skb, sch, qdisc, to_free);
0129 }
0130
0131 static int cbs_enqueue(struct sk_buff *skb, struct Qdisc *sch,
0132                struct sk_buff **to_free)
0133 {
0134     struct cbs_sched_data *q = qdisc_priv(sch);
0135
0136     return q->enqueue(skb, sch, to_free);
0137 }
0138
0139 /* timediff is in ns, slope is in bytes/s */
0140 static s64 timediff_to_credits(s64 timediff, s64 slope)
0141 {
0142     return div64_s64(timediff * slope, NSEC_PER_SEC);
0143 }
0144
0145 static s64 delay_from_credits(s64 credits, s64 slope)
0146 {
0147     if (unlikely(slope == 0))
0148         return S64_MAX;
0149
0150     return div64_s64(-credits * NSEC_PER_SEC, slope);
0151 }
0152
0153 static s64 credits_from_len(unsigned int len, s64 slope, s64 port_rate)
0154 {
0155     if (unlikely(port_rate == 0))
0156         return S64_MAX;
0157
0158     return div64_s64(len * slope, port_rate);
0159 }
0160
0161 static struct sk_buff *cbs_child_dequeue(struct Qdisc *sch, struct Qdisc *child)
0162 {
0163     struct sk_buff *skb;
0164
0165     skb = child->ops->dequeue(child);
0166     if (!skb)
0167         return NULL;
0168
0169     qdisc_qstats_backlog_dec(sch, skb);
0170     qdisc_bstats_update(sch, skb);
0171     sch->q.qlen--;
0172
0173     return skb;
0174 }
0175
0176 static struct sk_buff *cbs_dequeue_soft(struct Qdisc *sch)
0177 {
0178     struct cbs_sched_data *q = qdisc_priv(sch);
0179     struct Qdisc *qdisc = q->qdisc;
0180     s64 now = ktime_get_ns();
0181     struct sk_buff *skb;
0182     s64 credits;
0183     int len;
0184
0185     /* The previous packet is still being sent */
0186     if (now < q->last) {
0187         qdisc_watchdog_schedule_ns(&q->watchdog, q->last);
0188         return NULL;
0189     }
0190     if (q->credits < 0) {
0191         credits = timediff_to_credits(now - q->last, q->idleslope);
0192
0193         credits = q->credits + credits;
0194         q->credits = min_t(s64, credits, q->hicredit);
0195
0196         if (q->credits < 0) {
0197             s64 delay;
0198
0199             delay = delay_from_credits(q->credits, q->idleslope);
0200             qdisc_watchdog_schedule_ns(&q->watchdog, now + delay);
0201
0202             q->last = now;
0203
0204             return NULL;
0205         }
0206     }
0207     skb = cbs_child_dequeue(sch, qdisc);
0208     if (!skb)
0209         return NULL;
0210
0211     len = qdisc_pkt_len(skb);
0212
0213     /* As sendslope is a negative number, this will decrease the
0214      * amount of q->credits.
0215      */
0216     credits = credits_from_len(len, q->sendslope,
0217                    atomic64_read(&q->port_rate));
0218     credits += q->credits;
0219
0220     q->credits = max_t(s64, credits, q->locredit);
0221     /* Estimate of the transmission of the last byte of the packet in ns */
0222     if (unlikely(atomic64_read(&q->port_rate) == 0))
0223         q->last = now;
0224     else
0225         q->last = now + div64_s64(len * NSEC_PER_SEC,
0226                       atomic64_read(&q->port_rate));
0227
0228     return skb;
0229 }
0230
0231 static struct sk_buff *cbs_dequeue_offload(struct Qdisc *sch)
0232 {
0233     struct cbs_sched_data *q = qdisc_priv(sch);
0234     struct Qdisc *qdisc = q->qdisc;
0235
0236     return cbs_child_dequeue(sch, qdisc);
0237 }
0238
0239 static struct sk_buff *cbs_dequeue(struct Qdisc *sch)
0240 {
0241     struct cbs_sched_data *q = qdisc_priv(sch);
0242
0243     return q->dequeue(sch);
0244 }
0245
0246 static const struct nla_policy cbs_policy[TCA_CBS_MAX + 1] = {
0247     [TCA_CBS_PARMS] = { .len = sizeof(struct tc_cbs_qopt) },
0248 };
0249
0250 static void cbs_disable_offload(struct net_device *dev,
0251                 struct cbs_sched_data *q)
0252 {
0253     struct tc_cbs_qopt_offload cbs = { };
0254     const struct net_device_ops *ops;
0255     int err;
0256
0257     if (!q->offload)
0258         return;
0259
0260     q->enqueue = cbs_enqueue_soft;
0261     q->dequeue = cbs_dequeue_soft;
0262
0263     ops = dev->netdev_ops;
0264     if (!ops->ndo_setup_tc)
0265         return;
0266
0267     cbs.queue = q->queue;
0268     cbs.enable = 0;
0269
0270     err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
0271     if (err < 0)
0272         pr_warn("Couldn't disable CBS offload for queue %d\n",
0273             cbs.queue);
0274 }
0275
0276 static int cbs_enable_offload(struct net_device *dev, struct cbs_sched_data *q,
0277                   const struct tc_cbs_qopt *opt,
0278                   struct netlink_ext_ack *extack)
0279 {
0280     const struct net_device_ops *ops = dev->netdev_ops;
0281     struct tc_cbs_qopt_offload cbs = { };
0282     int err;
0283
0284     if (!ops->ndo_setup_tc) {
0285         NL_SET_ERR_MSG(extack, "Specified device does not support cbs offload");
0286         return -EOPNOTSUPP;
0287     }
0288
0289     cbs.queue = q->queue;
0290
0291     cbs.enable = 1;
0292     cbs.hicredit = opt->hicredit;
0293     cbs.locredit = opt->locredit;
0294     cbs.idleslope = opt->idleslope;
0295     cbs.sendslope = opt->sendslope;
0296
0297     err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
0298     if (err < 0) {
0299         NL_SET_ERR_MSG(extack, "Specified device failed to setup cbs hardware offload");
0300         return err;
0301     }
0302
0303     q->enqueue = cbs_enqueue_offload;
0304     q->dequeue = cbs_dequeue_offload;
0305
0306     return 0;
0307 }
0308
0309 static void cbs_set_port_rate(struct net_device *dev, struct cbs_sched_data *q)
0310 {
0311     struct ethtool_link_ksettings ecmd;
0312     int speed = SPEED_10;
0313     int port_rate;
0314     int err;
0315
0316     err = __ethtool_get_link_ksettings(dev, &ecmd);
0317     if (err < 0)
0318         goto skip;
0319
0320     if (ecmd.base.speed && ecmd.base.speed != SPEED_UNKNOWN)
0321         speed = ecmd.base.speed;
0322
0323 skip:
0324     port_rate = speed * 1000 * BYTES_PER_KBIT;
0325
0326     atomic64_set(&q->port_rate, port_rate);
0327     netdev_dbg(dev, "cbs: set %s's port_rate to: %lld, linkspeed: %d\n",
0328            dev->name, (long long)atomic64_read(&q->port_rate),
0329            ecmd.base.speed);
0330 }
0331
0332 static int cbs_dev_notifier(struct notifier_block *nb, unsigned long event,
0333                 void *ptr)
0334 {
0335     struct net_device *dev = netdev_notifier_info_to_dev(ptr);
0336     struct cbs_sched_data *q;
0337     struct net_device *qdev;
0338     bool found = false;
0339
0340     ASSERT_RTNL();
0341
0342     if (event != NETDEV_UP && event != NETDEV_CHANGE)
0343         return NOTIFY_DONE;
0344
0345     spin_lock(&cbs_list_lock);
0346     list_for_each_entry(q, &cbs_list, cbs_list) {
0347         qdev = qdisc_dev(q->qdisc);
0348         if (qdev == dev) {
0349             found = true;
0350             break;
0351         }
0352     }
0353     spin_unlock(&cbs_list_lock);
0354
0355     if (found)
0356         cbs_set_port_rate(dev, q);
0357
0358     return NOTIFY_DONE;
0359 }
0360
0361 static int cbs_change(struct Qdisc *sch, struct nlattr *opt,
0362               struct netlink_ext_ack *extack)
0363 {
0364     struct cbs_sched_data *q = qdisc_priv(sch);
0365     struct net_device *dev = qdisc_dev(sch);
0366     struct nlattr *tb[TCA_CBS_MAX + 1];
0367     struct tc_cbs_qopt *qopt;
0368     int err;
0369
0370     err = nla_parse_nested_deprecated(tb, TCA_CBS_MAX, opt, cbs_policy,
0371                       extack);
0372     if (err < 0)
0373         return err;
0374
0375     if (!tb[TCA_CBS_PARMS]) {
0376         NL_SET_ERR_MSG(extack, "Missing CBS parameter which are mandatory");
0377         return -EINVAL;
0378     }
0379
0380     qopt = nla_data(tb[TCA_CBS_PARMS]);
0381
0382     if (!qopt->offload) {
0383         cbs_set_port_rate(dev, q);
0384         cbs_disable_offload(dev, q);
0385     } else {
0386         err = cbs_enable_offload(dev, q, qopt, extack);
0387         if (err < 0)
0388             return err;
0389     }
0390
0391     /* Everything went OK, save the parameters used. */
0392     q->hicredit = qopt->hicredit;
0393     q->locredit = qopt->locredit;
0394     q->idleslope = qopt->idleslope * BYTES_PER_KBIT;
0395     q->sendslope = qopt->sendslope * BYTES_PER_KBIT;
0396     q->offload = qopt->offload;
0397
0398     return 0;
0399 }
0400
0401 static int cbs_init(struct Qdisc *sch, struct nlattr *opt,
0402             struct netlink_ext_ack *extack)
0403 {
0404     struct cbs_sched_data *q = qdisc_priv(sch);
0405     struct net_device *dev = qdisc_dev(sch);
0406
0407     if (!opt) {
0408         NL_SET_ERR_MSG(extack, "Missing CBS qdisc options  which are mandatory");
0409         return -EINVAL;
0410     }
0411
0412     q->qdisc = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
0413                      sch->handle, extack);
0414     if (!q->qdisc)
0415         return -ENOMEM;
0416
0417     spin_lock(&cbs_list_lock);
0418     list_add(&q->cbs_list, &cbs_list);
0419     spin_unlock(&cbs_list_lock);
0420
0421     qdisc_hash_add(q->qdisc, false);
0422
0423     q->queue = sch->dev_queue - netdev_get_tx_queue(dev, 0);
0424
0425     q->enqueue = cbs_enqueue_soft;
0426     q->dequeue = cbs_dequeue_soft;
0427
0428     qdisc_watchdog_init(&q->watchdog, sch);
0429
0430     return cbs_change(sch, opt, extack);
0431 }
0432
0433 static void cbs_destroy(struct Qdisc *sch)
0434 {
0435     struct cbs_sched_data *q = qdisc_priv(sch);
0436     struct net_device *dev = qdisc_dev(sch);
0437
0438     /* Nothing to do if we couldn't create the underlying qdisc */
0439     if (!q->qdisc)
0440         return;
0441
0442     qdisc_watchdog_cancel(&q->watchdog);
0443     cbs_disable_offload(dev, q);
0444
0445     spin_lock(&cbs_list_lock);
0446     list_del(&q->cbs_list);
0447     spin_unlock(&cbs_list_lock);
0448
0449     qdisc_put(q->qdisc);
0450 }
0451
0452 static int cbs_dump(struct Qdisc *sch, struct sk_buff *skb)
0453 {
0454     struct cbs_sched_data *q = qdisc_priv(sch);
0455     struct tc_cbs_qopt opt = { };
0456     struct nlattr *nest;
0457
0458     nest = nla_nest_start_noflag(skb, TCA_OPTIONS);
0459     if (!nest)
0460         goto nla_put_failure;
0461
0462     opt.hicredit = q->hicredit;
0463     opt.locredit = q->locredit;
0464     opt.sendslope = div64_s64(q->sendslope, BYTES_PER_KBIT);
0465     opt.idleslope = div64_s64(q->idleslope, BYTES_PER_KBIT);
0466     opt.offload = q->offload;
0467
0468     if (nla_put(skb, TCA_CBS_PARMS, sizeof(opt), &opt))
0469         goto nla_put_failure;
0470
0471     return nla_nest_end(skb, nest);
0472
0473 nla_put_failure:
0474     nla_nest_cancel(skb, nest);
0475     return -1;
0476 }
0477
0478 static int cbs_dump_class(struct Qdisc *sch, unsigned long cl,
0479               struct sk_buff *skb, struct tcmsg *tcm)
0480 {
0481     struct cbs_sched_data *q = qdisc_priv(sch);
0482
0483     if (cl != 1 || !q->qdisc)   /* only one class */
0484         return -ENOENT;
0485
0486     tcm->tcm_handle |= TC_H_MIN(1);
0487     tcm->tcm_info = q->qdisc->handle;
0488
0489     return 0;
0490 }
0491
0492 static int cbs_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new,
0493              struct Qdisc **old, struct netlink_ext_ack *extack)
0494 {
0495     struct cbs_sched_data *q = qdisc_priv(sch);
0496
0497     if (!new) {
0498         new = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
0499                     sch->handle, NULL);
0500         if (!new)
0501             new = &noop_qdisc;
0502     }
0503
0504     *old = qdisc_replace(sch, new, &q->qdisc);
0505     return 0;
0506 }
0507
0508 static struct Qdisc *cbs_leaf(struct Qdisc *sch, unsigned long arg)
0509 {
0510     struct cbs_sched_data *q = qdisc_priv(sch);
0511
0512     return q->qdisc;
0513 }
0514
0515 static unsigned long cbs_find(struct Qdisc *sch, u32 classid)
0516 {
0517     return 1;
0518 }
0519
0520 static void cbs_walk(struct Qdisc *sch, struct qdisc_walker *walker)
0521 {
0522     if (!walker->stop) {
0523         if (walker->count >= walker->skip) {
0524             if (walker->fn(sch, 1, walker) < 0) {
0525                 walker->stop = 1;
0526                 return;
0527             }
0528         }
0529         walker->count++;
0530     }
0531 }
0532
0533 static const struct Qdisc_class_ops cbs_class_ops = {
0534     .graft      =   cbs_graft,
0535     .leaf       =   cbs_leaf,
0536     .find       =   cbs_find,
0537     .walk       =   cbs_walk,
0538     .dump       =   cbs_dump_class,
0539 };
0540
0541 static struct Qdisc_ops cbs_qdisc_ops __read_mostly = {
0542     .id     =   "cbs",
0543     .cl_ops     =   &cbs_class_ops,
0544     .priv_size  =   sizeof(struct cbs_sched_data),
0545     .enqueue    =   cbs_enqueue,
0546     .dequeue    =   cbs_dequeue,
0547     .peek       =   qdisc_peek_dequeued,
0548     .init       =   cbs_init,
0549     .reset      =   qdisc_reset_queue,
0550     .destroy    =   cbs_destroy,
0551     .change     =   cbs_change,
0552     .dump       =   cbs_dump,
0553     .owner      =   THIS_MODULE,
0554 };
0555
0556 static struct notifier_block cbs_device_notifier = {
0557     .notifier_call = cbs_dev_notifier,
0558 };
0559
0560 static int __init cbs_module_init(void)
0561 {
0562     int err;
0563
0564     err = register_netdevice_notifier(&cbs_device_notifier);
0565     if (err)
0566         return err;
0567
0568     err = register_qdisc(&cbs_qdisc_ops);
0569     if (err)
0570         unregister_netdevice_notifier(&cbs_device_notifier);
0571
0572     return err;
0573 }
0574
0575 static void __exit cbs_module_exit(void)
0576 {
0577     unregister_qdisc(&cbs_qdisc_ops);
0578     unregister_netdevice_notifier(&cbs_device_notifier);
0579 }
0580 module_init(cbs_module_init)
0581 module_exit(cbs_module_exit)
0582 MODULE_LICENSE("GPL");