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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* net/sched/sch_cbs.c Credit Based Shaper
*
* Authors: Vinicius Costa Gomes <vinicius.gomes@intel.com>
*/
/* Credit Based Shaper (CBS)
* =========================
*
* This is a simple rate-limiting shaper aimed at TSN applications on
* systems with known traffic workloads.
*
* Its algorithm is defined by the IEEE 802.1Q-2014 Specification,
* Section 8.6.8.2, and explained in more detail in the Annex L of the
* same specification.
*
* There are four tunables to be considered:
*
* 'idleslope': Idleslope is the rate of credits that is
* accumulated (in kilobits per second) when there is at least
* one packet waiting for transmission. Packets are transmitted
* when the current value of credits is equal or greater than
* zero. When there is no packet to be transmitted the amount of
* credits is set to zero. This is the main tunable of the CBS
* algorithm.
*
* 'sendslope':
* Sendslope is the rate of credits that is depleted (it should be a
* negative number of kilobits per second) when a transmission is
* ocurring. It can be calculated as follows, (IEEE 802.1Q-2014 Section
* 8.6.8.2 item g):
*
* sendslope = idleslope - port_transmit_rate
*
* 'hicredit': Hicredit defines the maximum amount of credits (in
* bytes) that can be accumulated. Hicredit depends on the
* characteristics of interfering traffic,
* 'max_interference_size' is the maximum size of any burst of
* traffic that can delay the transmission of a frame that is
* available for transmission for this traffic class, (IEEE
* 802.1Q-2014 Annex L, Equation L-3):
*
* hicredit = max_interference_size * (idleslope / port_transmit_rate)
*
* 'locredit': Locredit is the minimum amount of credits that can
* be reached. It is a function of the traffic flowing through
* this qdisc (IEEE 802.1Q-2014 Annex L, Equation L-2):
*
* locredit = max_frame_size * (sendslope / port_transmit_rate)
*/
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <net/netevent.h>
#include <net/netlink.h>
#include <net/sch_generic.h>
#include <net/pkt_sched.h>
static LIST_HEAD(cbs_list);
static DEFINE_SPINLOCK(cbs_list_lock);
#define BYTES_PER_KBIT (1000LL / 8)
struct cbs_sched_data {
bool offload;
int queue;
atomic64_t port_rate; /* in bytes/s */
s64 last; /* timestamp in ns */
s64 credits; /* in bytes */
s32 locredit; /* in bytes */
s32 hicredit; /* in bytes */
s64 sendslope; /* in bytes/s */
s64 idleslope; /* in bytes/s */
struct qdisc_watchdog watchdog;
int (*enqueue)(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free);
struct sk_buff *(*dequeue)(struct Qdisc *sch);
struct Qdisc *qdisc;
struct list_head cbs_list;
};
static int cbs_child_enqueue(struct sk_buff *skb, struct Qdisc *sch,
struct Qdisc *child,
struct sk_buff **to_free)
{
unsigned int len = qdisc_pkt_len(skb);
int err;
err = child->ops->enqueue(skb, child, to_free);
if (err != NET_XMIT_SUCCESS)
return err;
sch->qstats.backlog += len;
sch->q.qlen++;
return NET_XMIT_SUCCESS;
}
static int cbs_enqueue_offload(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free)
{
struct cbs_sched_data *q = qdisc_priv(sch);
struct Qdisc *qdisc = q->qdisc;
return cbs_child_enqueue(skb, sch, qdisc, to_free);
}
static int cbs_enqueue_soft(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free)
{
struct cbs_sched_data *q = qdisc_priv(sch);
struct Qdisc *qdisc = q->qdisc;
if (sch->q.qlen == 0 && q->credits > 0) {
/* We need to stop accumulating credits when there's
* no enqueued packets and q->credits is positive.
*/
q->credits = 0;
q->last = ktime_get_ns();
}
return cbs_child_enqueue(skb, sch, qdisc, to_free);
}
static int cbs_enqueue(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free)
{
struct cbs_sched_data *q = qdisc_priv(sch);
return q->enqueue(skb, sch, to_free);
}
/* timediff is in ns, slope is in bytes/s */
static s64 timediff_to_credits(s64 timediff, s64 slope)
{
return div64_s64(timediff * slope, NSEC_PER_SEC);
}
static s64 delay_from_credits(s64 credits, s64 slope)
{
if (unlikely(slope == 0))
return S64_MAX;
return div64_s64(-credits * NSEC_PER_SEC, slope);
}
static s64 credits_from_len(unsigned int len, s64 slope, s64 port_rate)
{
if (unlikely(port_rate == 0))
return S64_MAX;
return div64_s64(len * slope, port_rate);
}
static struct sk_buff *cbs_child_dequeue(struct Qdisc *sch, struct Qdisc *child)
{
struct sk_buff *skb;
skb = child->ops->dequeue(child);
if (!skb)
return NULL;
qdisc_qstats_backlog_dec(sch, skb);
qdisc_bstats_update(sch, skb);
sch->q.qlen--;
return skb;
}
static struct sk_buff *cbs_dequeue_soft(struct Qdisc *sch)
{
struct cbs_sched_data *q = qdisc_priv(sch);
struct Qdisc *qdisc = q->qdisc;
s64 now = ktime_get_ns();
struct sk_buff *skb;
s64 credits;
int len;
if (q->credits < 0) {
credits = timediff_to_credits(now - q->last, q->idleslope);
credits = q->credits + credits;
q->credits = min_t(s64, credits, q->hicredit);
if (q->credits < 0) {
s64 delay;
delay = delay_from_credits(q->credits, q->idleslope);
qdisc_watchdog_schedule_ns(&q->watchdog, now + delay);
q->last = now;
return NULL;
}
}
skb = cbs_child_dequeue(sch, qdisc);
if (!skb)
return NULL;
len = qdisc_pkt_len(skb);
/* As sendslope is a negative number, this will decrease the
* amount of q->credits.
*/
credits = credits_from_len(len, q->sendslope,
atomic64_read(&q->port_rate));
credits += q->credits;
q->credits = max_t(s64, credits, q->locredit);
q->last = now;
return skb;
}
static struct sk_buff *cbs_dequeue_offload(struct Qdisc *sch)
{
struct cbs_sched_data *q = qdisc_priv(sch);
struct Qdisc *qdisc = q->qdisc;
return cbs_child_dequeue(sch, qdisc);
}
static struct sk_buff *cbs_dequeue(struct Qdisc *sch)
{
struct cbs_sched_data *q = qdisc_priv(sch);
return q->dequeue(sch);
}
static const struct nla_policy cbs_policy[TCA_CBS_MAX + 1] = {
[TCA_CBS_PARMS] = { .len = sizeof(struct tc_cbs_qopt) },
};
static void cbs_disable_offload(struct net_device *dev,
struct cbs_sched_data *q)
{
struct tc_cbs_qopt_offload cbs = { };
const struct net_device_ops *ops;
int err;
if (!q->offload)
return;
q->enqueue = cbs_enqueue_soft;
q->dequeue = cbs_dequeue_soft;
ops = dev->netdev_ops;
if (!ops->ndo_setup_tc)
return;
cbs.queue = q->queue;
cbs.enable = 0;
err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
if (err < 0)
pr_warn("Couldn't disable CBS offload for queue %d\n",
cbs.queue);
}
static int cbs_enable_offload(struct net_device *dev, struct cbs_sched_data *q,
const struct tc_cbs_qopt *opt,
struct netlink_ext_ack *extack)
{
const struct net_device_ops *ops = dev->netdev_ops;
struct tc_cbs_qopt_offload cbs = { };
int err;
if (!ops->ndo_setup_tc) {
NL_SET_ERR_MSG(extack, "Specified device does not support cbs offload");
return -EOPNOTSUPP;
}
cbs.queue = q->queue;
cbs.enable = 1;
cbs.hicredit = opt->hicredit;
cbs.locredit = opt->locredit;
cbs.idleslope = opt->idleslope;
cbs.sendslope = opt->sendslope;
err = ops->ndo_setup_tc(dev, TC_SETUP_QDISC_CBS, &cbs);
if (err < 0) {
NL_SET_ERR_MSG(extack, "Specified device failed to setup cbs hardware offload");
return err;
}
q->enqueue = cbs_enqueue_offload;
q->dequeue = cbs_dequeue_offload;
return 0;
}
static void cbs_set_port_rate(struct net_device *dev, struct cbs_sched_data *q)
{
struct ethtool_link_ksettings ecmd;
int speed = SPEED_10;
int port_rate;
int err;
err = __ethtool_get_link_ksettings(dev, &ecmd);
if (err < 0)
goto skip;
if (ecmd.base.speed && ecmd.base.speed != SPEED_UNKNOWN)
speed = ecmd.base.speed;
skip:
port_rate = speed * 1000 * BYTES_PER_KBIT;
atomic64_set(&q->port_rate, port_rate);
netdev_dbg(dev, "cbs: set %s's port_rate to: %lld, linkspeed: %d\n",
dev->name, (long long)atomic64_read(&q->port_rate),
ecmd.base.speed);
}
static int cbs_dev_notifier(struct notifier_block *nb, unsigned long event,
void *ptr)
{
struct net_device *dev = netdev_notifier_info_to_dev(ptr);
struct cbs_sched_data *q;
struct net_device *qdev;
bool found = false;
ASSERT_RTNL();
if (event != NETDEV_UP && event != NETDEV_CHANGE)
return NOTIFY_DONE;
spin_lock(&cbs_list_lock);
list_for_each_entry(q, &cbs_list, cbs_list) {
qdev = qdisc_dev(q->qdisc);
if (qdev == dev) {
found = true;
break;
}
}
spin_unlock(&cbs_list_lock);
if (found)
cbs_set_port_rate(dev, q);
return NOTIFY_DONE;
}
static int cbs_change(struct Qdisc *sch, struct nlattr *opt,
struct netlink_ext_ack *extack)
{
struct cbs_sched_data *q = qdisc_priv(sch);
struct net_device *dev = qdisc_dev(sch);
struct nlattr *tb[TCA_CBS_MAX + 1];
struct tc_cbs_qopt *qopt;
int err;
err = nla_parse_nested_deprecated(tb, TCA_CBS_MAX, opt, cbs_policy,
extack);
if (err < 0)
return err;
if (!tb[TCA_CBS_PARMS]) {
NL_SET_ERR_MSG(extack, "Missing CBS parameter which are mandatory");
return -EINVAL;
}
qopt = nla_data(tb[TCA_CBS_PARMS]);
if (!qopt->offload) {
cbs_set_port_rate(dev, q);
cbs_disable_offload(dev, q);
} else {
err = cbs_enable_offload(dev, q, qopt, extack);
if (err < 0)
return err;
}
/* Everything went OK, save the parameters used. */
q->hicredit = qopt->hicredit;
q->locredit = qopt->locredit;
q->idleslope = qopt->idleslope * BYTES_PER_KBIT;
q->sendslope = qopt->sendslope * BYTES_PER_KBIT;
q->offload = qopt->offload;
return 0;
}
static int cbs_init(struct Qdisc *sch, struct nlattr *opt,
struct netlink_ext_ack *extack)
{
struct cbs_sched_data *q = qdisc_priv(sch);
struct net_device *dev = qdisc_dev(sch);
if (!opt) {
NL_SET_ERR_MSG(extack, "Missing CBS qdisc options which are mandatory");
return -EINVAL;
}
q->qdisc = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
sch->handle, extack);
if (!q->qdisc)
return -ENOMEM;
spin_lock(&cbs_list_lock);
list_add(&q->cbs_list, &cbs_list);
spin_unlock(&cbs_list_lock);
qdisc_hash_add(q->qdisc, false);
q->queue = sch->dev_queue - netdev_get_tx_queue(dev, 0);
q->enqueue = cbs_enqueue_soft;
q->dequeue = cbs_dequeue_soft;
qdisc_watchdog_init(&q->watchdog, sch);
return cbs_change(sch, opt, extack);
}
static void cbs_destroy(struct Qdisc *sch)
{
struct cbs_sched_data *q = qdisc_priv(sch);
struct net_device *dev = qdisc_dev(sch);
/* Nothing to do if we couldn't create the underlying qdisc */
if (!q->qdisc)
return;
qdisc_watchdog_cancel(&q->watchdog);
cbs_disable_offload(dev, q);
spin_lock(&cbs_list_lock);
list_del(&q->cbs_list);
spin_unlock(&cbs_list_lock);
qdisc_put(q->qdisc);
}
static int cbs_dump(struct Qdisc *sch, struct sk_buff *skb)
{
struct cbs_sched_data *q = qdisc_priv(sch);
struct tc_cbs_qopt opt = { };
struct nlattr *nest;
nest = nla_nest_start_noflag(skb, TCA_OPTIONS);
if (!nest)
goto nla_put_failure;
opt.hicredit = q->hicredit;
opt.locredit = q->locredit;
opt.sendslope = div64_s64(q->sendslope, BYTES_PER_KBIT);
opt.idleslope = div64_s64(q->idleslope, BYTES_PER_KBIT);
opt.offload = q->offload;
if (nla_put(skb, TCA_CBS_PARMS, sizeof(opt), &opt))
goto nla_put_failure;
return nla_nest_end(skb, nest);
nla_put_failure:
nla_nest_cancel(skb, nest);
return -1;
}
static int cbs_dump_class(struct Qdisc *sch, unsigned long cl,
struct sk_buff *skb, struct tcmsg *tcm)
{
struct cbs_sched_data *q = qdisc_priv(sch);
if (cl != 1 || !q->qdisc) /* only one class */
return -ENOENT;
tcm->tcm_handle |= TC_H_MIN(1);
tcm->tcm_info = q->qdisc->handle;
return 0;
}
static int cbs_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new,
struct Qdisc **old, struct netlink_ext_ack *extack)
{
struct cbs_sched_data *q = qdisc_priv(sch);
if (!new) {
new = qdisc_create_dflt(sch->dev_queue, &pfifo_qdisc_ops,
sch->handle, NULL);
if (!new)
new = &noop_qdisc;
}
*old = qdisc_replace(sch, new, &q->qdisc);
return 0;
}
static struct Qdisc *cbs_leaf(struct Qdisc *sch, unsigned long arg)
{
struct cbs_sched_data *q = qdisc_priv(sch);
return q->qdisc;
}
static unsigned long cbs_find(struct Qdisc *sch, u32 classid)
{
return 1;
}
static void cbs_walk(struct Qdisc *sch, struct qdisc_walker *walker)
{
if (!walker->stop) {
if (walker->count >= walker->skip) {
if (walker->fn(sch, 1, walker) < 0) {
walker->stop = 1;
return;
}
}
walker->count++;
}
}
static const struct Qdisc_class_ops cbs_class_ops = {
.graft = cbs_graft,
.leaf = cbs_leaf,
.find = cbs_find,
.walk = cbs_walk,
.dump = cbs_dump_class,
};
static struct Qdisc_ops cbs_qdisc_ops __read_mostly = {
.id = "cbs",
.cl_ops = &cbs_class_ops,
.priv_size = sizeof(struct cbs_sched_data),
.enqueue = cbs_enqueue,
.dequeue = cbs_dequeue,
.peek = qdisc_peek_dequeued,
.init = cbs_init,
.reset = qdisc_reset_queue,
.destroy = cbs_destroy,
.change = cbs_change,
.dump = cbs_dump,
.owner = THIS_MODULE,
};
static struct notifier_block cbs_device_notifier = {
.notifier_call = cbs_dev_notifier,
};
static int __init cbs_module_init(void)
{
int err;
err = register_netdevice_notifier(&cbs_device_notifier);
if (err)
return err;
err = register_qdisc(&cbs_qdisc_ops);
if (err)
unregister_netdevice_notifier(&cbs_device_notifier);
return err;
}
static void __exit cbs_module_exit(void)
{
unregister_qdisc(&cbs_qdisc_ops);
unregister_netdevice_notifier(&cbs_device_notifier);
}
module_init(cbs_module_init)
module_exit(cbs_module_exit)
MODULE_LICENSE("GPL");
|