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/*
* net/sched/sch_cbs.c Credit Based Shaper
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
* 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/netlink.h>
#include <net/sch_generic.h>
#include <net/pkt_sched.h>
#define BYTES_PER_KBIT (1000LL / 8)
struct cbs_sched_data {
bool offload;
int queue;
s64 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 *(*dequeue)(struct Qdisc *sch);
};
static int cbs_enqueue_offload(struct sk_buff *skb, struct Qdisc *sch)
{
return qdisc_enqueue_tail(skb, sch);
}
static int cbs_enqueue_soft(struct sk_buff *skb, struct Qdisc *sch)
{
struct cbs_sched_data *q = qdisc_priv(sch);
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 qdisc_enqueue_tail(skb, sch);
}
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);
}
/* 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_dequeue_soft(struct Qdisc *sch)
{
struct cbs_sched_data *q = qdisc_priv(sch);
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 = qdisc_dequeue_head(sch);
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, 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)
{
return qdisc_dequeue_head(sch);
}
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)
{
const struct net_device_ops *ops = dev->netdev_ops;
struct tc_cbs_qopt_offload cbs = { };
int err;
if (!ops->ndo_setup_tc)
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)
return err;
q->enqueue = cbs_enqueue_offload;
q->dequeue = cbs_dequeue_offload;
return 0;
}
static int cbs_change(struct Qdisc *sch, struct nlattr *opt)
{
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(tb, TCA_CBS_MAX, opt, cbs_policy, NULL);
if (err < 0)
return err;
if (!tb[TCA_CBS_PARMS])
return -EINVAL;
qopt = nla_data(tb[TCA_CBS_PARMS]);
if (!qopt->offload) {
struct ethtool_link_ksettings ecmd;
s64 link_speed;
if (!__ethtool_get_link_ksettings(dev, &ecmd))
link_speed = ecmd.base.speed;
else
link_speed = SPEED_1000;
q->port_rate = link_speed * 1000 * BYTES_PER_KBIT;
cbs_disable_offload(dev, q);
} else {
err = cbs_enable_offload(dev, q, qopt);
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
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