/* Copyright (C) 2013 Cisco Systems, Inc, 2013.
*
* 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.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* Author: Vijay Subramanian <vijaynsu@cisco.com>
* Author: Mythili Prabhu <mysuryan@cisco.com>
*
* ECN support is added by Naeem Khademi <naeemk@ifi.uio.no>
* University of Oslo, Norway.
*
* References:
* IETF draft submission: http://tools.ietf.org/html/draft-pan-aqm-pie-00
* IEEE Conference on High Performance Switching and Routing 2013 :
* "PIE: A * Lightweight Control Scheme to Address the Bufferbloat Problem"
*/
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <net/pkt_sched.h>
#include <net/inet_ecn.h>
#define QUEUE_THRESHOLD 10000
#define DQCOUNT_INVALID -1
#define MAX_PROB 0xffffffff
#define PIE_SCALE 8
/* parameters used */
struct pie_params {
psched_time_t target; /* user specified target delay in pschedtime */
u32 tupdate; /* timer frequency (in jiffies) */
u32 limit; /* number of packets that can be enqueued */
u32 alpha; /* alpha and beta are between 0 and 32 */
u32 beta; /* and are used for shift relative to 1 */
bool ecn; /* true if ecn is enabled */
bool bytemode; /* to scale drop early prob based on pkt size */
};
/* variables used */
struct pie_vars {
u32 prob; /* probability but scaled by u32 limit. */
psched_time_t burst_time;
psched_time_t qdelay;
psched_time_t qdelay_old;
u64 dq_count; /* measured in bytes */
psched_time_t dq_tstamp; /* drain rate */
u32 avg_dq_rate; /* bytes per pschedtime tick,scaled */
u32 qlen_old; /* in bytes */
};
/* statistics gathering */
struct pie_stats {
u32 packets_in; /* total number of packets enqueued */
u32 dropped; /* packets dropped due to pie_action */
u32 overlimit; /* dropped due to lack of space in queue */
u32 maxq; /* maximum queue size */
u32 ecn_mark; /* packets marked with ECN */
};
/* private data for the Qdisc */
struct pie_sched_data {
struct pie_params params;
struct pie_vars vars;
struct pie_stats stats;
struct timer_list adapt_timer;
};
static void pie_params_init(struct pie_params *params)
{
params->alpha = 2;
params->beta = 20;
params->tupdate = usecs_to_jiffies(30 * USEC_PER_MSEC); /* 30 ms */
params->limit = 1000; /* default of 1000 packets */
params->target = PSCHED_NS2TICKS(20 * NSEC_PER_MSEC); /* 20 ms */
params->ecn = false;
params->bytemode = false;
}
static void pie_vars_init(struct pie_vars *vars)
{
vars->dq_count = DQCOUNT_INVALID;
vars->avg_dq_rate = 0;
/* default of 100 ms in pschedtime */
vars->burst_time = PSCHED_NS2TICKS(100 * NSEC_PER_MSEC);
}
static bool drop_early(struct Qdisc *sch, u32 packet_size)
{
struct pie_sched_data *q = qdisc_priv(sch);
u32 rnd;
u32 local_prob = q->vars.prob;
u32 mtu = psched_mtu(qdisc_dev(sch));
/* If there is still burst allowance left skip random early drop */
if (q->vars.burst_time > 0)
return false;
/* If current delay is less than half of target, and
* if drop prob is low already, disable early_drop
*/
if ((q->vars.qdelay < q->params.target / 2)
&& (q->vars.prob < MAX_PROB / 5))
return false;
/* If we have fewer than 2 mtu-sized packets, disable drop_early,
* similar to min_th in RED
*/
if (sch->qstats.backlog < 2 * mtu)
return false;
/* If bytemode is turned on, use packet size to compute new
* probablity. Smaller packets will have lower drop prob in this case
*/
if (q->params.bytemode && packet_size <= mtu)
local_prob = (local_prob / mtu) * packet_size;
else
local_prob = q->vars.prob;
rnd = prandom_u32();
if (rnd < local_prob)
return true;
return false;
}
static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
struct pie_sched_data *q = qdisc_priv(sch);
bool enqueue = false;
if (unlikely(qdisc_qlen(sch) >= sch->limit)) {
q->stats.overlimit++;
goto out;
}
if (!drop_early(sch, skb->len)) {
enqueue = true;
} else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) &&
INET_ECN_set_ce(skb)) {
/* If packet is ecn capable, mark it if drop probability
* is lower than 10%, else drop it.
*/
q->stats.ecn_mark++;
enqueue = true;
}
/* we can enqueue the packet */
if (enqueue) {
q->stats.packets_in++;
if (qdisc_qlen(sch) > q->stats.maxq)
q->stats.maxq = qdisc_qlen(sch);
return qdisc_enqueue_tail(skb, sch);
}
out:
q->stats.dropped++;
return qdisc_drop(skb, sch);
}
static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = {
[TCA_PIE_TARGET] = {.type = NLA_U32},
[TCA_PIE_LIMIT] = {.type = NLA_U32},
[TCA_PIE_TUPDATE] = {.type = NLA_U32},
[TCA_PIE_ALPHA] = {.type = NLA_U32},
[TCA_PIE_BETA] = {.type = NLA_U32},
[TCA_PIE_ECN] = {.type = NLA_U32},
[TCA_PIE_BYTEMODE] = {.type = NLA_U32},
};
static int pie_change(struct Qdisc *sch, struct nlattr *opt)
{
struct pie_sched_data *q = qdisc_priv(sch);
struct nlattr *tb[TCA_PIE_MAX + 1];
unsigned int qlen;
int err;
if (!opt)
return -EINVAL;
err = nla_parse_nested(tb, TCA_PIE_MAX, opt, pie_policy);
if (err < 0)
return err;
sch_tree_lock(sch);
/* convert from microseconds to pschedtime */
if (tb[TCA_PIE_TARGET]) {
/* target is in us */
u32 target = nla_get_u32(tb[TCA_PIE_TARGET]);
/* convert to pschedtime */
q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC);
}
/* tupdate is in jiffies */
if (tb[TCA_PIE_TUPDATE])
q->params.tupdate = usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE]));
if (tb[TCA_PIE_LIMIT]) {
u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]);
q->params.limit = limit;
sch->limit = limit;
}
if (tb[TCA_PIE_ALPHA])
q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]);
if (tb[TCA_PIE_BETA])
q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]);
if (tb[TCA_PIE_ECN])
q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]);
if (tb[TCA_PIE_BYTEMODE])
q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]);
/* Drop excess packets if new limit is lower */
qlen = sch->q.qlen;
while (sch->q.qlen > sch->limit) {
struct sk_buff *skb = __skb_dequeue(&sch->q);
qdisc_qstats_backlog_dec(sch, skb);
qdisc_drop(skb, sch);
}
qdisc_tree_decrease_qlen(sch, qlen - sch->q.qlen);
sch_tree_unlock(sch);
return 0;
}
static void pie_process_dequeue(struct Qdisc *sch, struct sk_buff *skb)
{
struct pie_sched_data *q = qdisc_priv(sch);
int qlen = sch->qstats.backlog; /* current queue size in bytes */
/* If current queue is about 10 packets or more and dq_count is unset
* we have enough packets to calculate the drain rate. Save
* current time as dq_tstamp and start measurement cycle.
*/
if (qlen >= QUEUE_THRESHOLD && q->vars.dq_count == DQCOUNT_INVALID) {
q->vars.dq_tstamp = psched_get_time();
q->vars.dq_count = 0;
}
/* Calculate the average drain rate from this value. If queue length
* has receded to a small value viz., <= QUEUE_THRESHOLD bytes,reset
* the dq_count to -1 as we don't have enough packets to calculate the
* drain rate anymore The following if block is entered only when we
* have a substantial queue built up (QUEUE_THRESHOLD bytes or more)
* and we calculate the drain rate for the threshold here. dq_count is
* in bytes, time difference in psched_time, hence rate is in
* bytes/psched_time.
*/
if (q->vars.dq_count != DQCOUNT_INVALID) {
q->vars.dq_count += skb->len;
if (q->vars.dq_count >= QUEUE_THRESHOLD) {
psched_time_t now = psched_get_time();
u32 dtime = now - q->vars.dq_tstamp;
u32 count = q->vars.dq_count << PIE_SCALE;
if (dtime == 0)
return;
count = count / dtime;
if (q->vars.avg_dq_rate == 0)
q->vars.avg_dq_rate = count;
else
q->vars.avg_dq_rate =
(q->vars.avg_dq_rate -
(q->vars.avg_dq_rate >> 3)) + (count >> 3);
/* If the queue has receded below the threshold, we hold
* on to the last drain rate calculated, else we reset
* dq_count to 0 to re-enter the if block when the next
* packet is dequeued
*/
if (qlen < QUEUE_THRESHOLD)
q->vars.dq_count = DQCOUNT_INVALID;
else {
q->vars.dq_count = 0;
q->vars.dq_tstamp = psched_get_time();
}
if (q->vars.burst_time > 0) {
if (q->vars.burst_time > dtime)
q->vars.burst_time -= dtime;
else
q->vars.burst_time = 0;
}
}
}
}
static void calculate_probability(struct Qdisc *sch)
{
struct pie_sched_data *q = qdisc_priv(sch);
u32 qlen = sch->qstats.backlog; /* queue size in bytes */
psched_time_t qdelay = 0; /* in pschedtime */
psched_time_t qdelay_old = q->vars.qdelay; /* in pschedtime */
s32 delta = 0; /* determines the change in probability */
u32 oldprob;
u32 alpha, beta;
bool update_prob = true;
q->vars.qdelay_old = q->vars.qdelay;
if (q->vars.avg_dq_rate > 0)
qdelay = (qlen << PIE_SCALE) / q->vars.avg_dq_rate;
else
qdelay = 0;
/* If qdelay is zero and qlen is not, it means qlen is very small, less
* than dequeue_rate, so we do not update probabilty in this round
*/
if (qdelay == 0 && qlen != 0)
update_prob = false;
/* In the algorithm, alpha and beta are between 0 and 2 with typical
* value for alpha as 0.125. In this implementation, we use values 0-32
* passed from user space to represent this. Also, alpha and beta have
* unit of HZ and need to be scaled before they can used to update
* probability. alpha/beta are updated locally below by 1) scaling them
* appropriately 2) scaling down by 16 to come to 0-2 range.
* Please see paper for details.
*
* We scale alpha and beta differently depending on whether we are in
* light, medium or high dropping mode.
*/
if (q->vars.prob < MAX_PROB / 100) {
alpha =
(q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
beta =
(q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
} else if (q->vars.prob < MAX_PROB / 10) {
alpha =
(q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
beta =
(q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
} else {
alpha =
(q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
beta =
(q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
}
/* alpha and beta should be between 0 and 32, in multiples of 1/16 */
delta += alpha * ((qdelay - q->params.target));
delta += beta * ((qdelay - qdelay_old));
oldprob = q->vars.prob;
/* to ensure we increase probability in steps of no more than 2% */
if (delta > (s32) (MAX_PROB / (100 / 2)) &&
q->vars.prob >= MAX_PROB / 10)
delta = (MAX_PROB / 100) * 2;
/* Non-linear drop:
* Tune drop probability to increase quickly for high delays(>= 250ms)
* 250ms is derived through experiments and provides error protection
*/
if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC)))
delta += MAX_PROB / (100 / 2);
q->vars.prob += delta;
if (delta > 0) {
/* prevent overflow */
if (q->vars.prob < oldprob) {
q->vars.prob = MAX_PROB;
/* Prevent normalization error. If probability is at
* maximum value already, we normalize it here, and
* skip the check to do a non-linear drop in the next
* section.
*/
update_prob = false;
}
} else {
/* prevent underflow */
if (q->vars.prob > oldprob)
q->vars.prob = 0;
}
/* Non-linear drop in probability: Reduce drop probability quickly if
* delay is 0 for 2 consecutive Tupdate periods.
*/
if ((qdelay == 0) && (qdelay_old == 0) && update_prob)
q->vars.prob = (q->vars.prob * 98) / 100;
q->vars.qdelay = qdelay;
q->vars.qlen_old = qlen;
/* We restart the measurement cycle if the following conditions are met
* 1. If the delay has been low for 2 consecutive Tupdate periods
* 2. Calculated drop probability is zero
* 3. We have atleast one estimate for the avg_dq_rate ie.,
* is a non-zero value
*/
if ((q->vars.qdelay < q->params.target / 2) &&
(q->vars.qdelay_old < q->params.target / 2) &&
(q->vars.prob == 0) &&
(q->vars.avg_dq_rate > 0))
pie_vars_init(&q->vars);
}
static void pie_timer(unsigned long arg)
{
struct Qdisc *sch = (struct Qdisc *)arg;
struct pie_sched_data *q = qdisc_priv(sch);
spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));
spin_lock(root_lock);
calculate_probability(sch);
/* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */
if (q->params.tupdate)
mod_timer(&q->adapt_timer, jiffies + q->params.tupdate);
spin_unlock(root_lock);
}
static int pie_init(struct Qdisc *sch, struct nlattr *opt)
{
struct pie_sched_data *q = qdisc_priv(sch);
pie_params_init(&q->params);
pie_vars_init(&q->vars);
sch->limit = q->params.limit;
setup_timer(&q->adapt_timer, pie_timer, (unsigned long)sch);
if (opt) {
int err = pie_change(sch, opt);
if (err)
return err;
}
mod_timer(&q->adapt_timer, jiffies + HZ / 2);
return 0;
}
static int pie_dump(struct Qdisc *sch, struct sk_buff *skb)
{
struct pie_sched_data *q = qdisc_priv(sch);
struct nlattr *opts;
opts = nla_nest_start(skb, TCA_OPTIONS);
if (opts == NULL)
goto nla_put_failure;
/* convert target from pschedtime to us */
if (nla_put_u32(skb, TCA_PIE_TARGET,
((u32) PSCHED_TICKS2NS(q->params.target)) /
NSEC_PER_USEC) ||
nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) ||
nla_put_u32(skb, TCA_PIE_TUPDATE, jiffies_to_usecs(q->params.tupdate)) ||
nla_put_u32(skb, TCA_PIE_ALPHA, q->params.alpha) ||
nla_put_u32(skb, TCA_PIE_BETA, q->params.beta) ||
nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) ||
nla_put_u32(skb, TCA_PIE_BYTEMODE, q->params.bytemode))
goto nla_put_failure;
return nla_nest_end(skb, opts);
nla_put_failure:
nla_nest_cancel(skb, opts);
return -1;
}
static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
{
struct pie_sched_data *q = qdisc_priv(sch);
struct tc_pie_xstats st = {
.prob = q->vars.prob,
.delay = ((u32) PSCHED_TICKS2NS(q->vars.qdelay)) /
NSEC_PER_USEC,
/* unscale and return dq_rate in bytes per sec */
.avg_dq_rate = q->vars.avg_dq_rate *
(PSCHED_TICKS_PER_SEC) >> PIE_SCALE,
.packets_in = q->stats.packets_in,
.overlimit = q->stats.overlimit,
.maxq = q->stats.maxq,
.dropped = q->stats.dropped,
.ecn_mark = q->stats.ecn_mark,
};
return gnet_stats_copy_app(d, &st, sizeof(st));
}
static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch)
{
struct sk_buff *skb;
skb = __qdisc_dequeue_head(sch, &sch->q);
if (!skb)
return NULL;
pie_process_dequeue(sch, skb);
return skb;
}
static void pie_reset(struct Qdisc *sch)
{
struct pie_sched_data *q = qdisc_priv(sch);
qdisc_reset_queue(sch);
pie_vars_init(&q->vars);
}
static void pie_destroy(struct Qdisc *sch)
{
struct pie_sched_data *q = qdisc_priv(sch);
q->params.tupdate = 0;
del_timer_sync(&q->adapt_timer);
}
static struct Qdisc_ops pie_qdisc_ops __read_mostly = {
.id = "pie",
.priv_size = sizeof(struct pie_sched_data),
.enqueue = pie_qdisc_enqueue,
.dequeue = pie_qdisc_dequeue,
.peek = qdisc_peek_dequeued,
.init = pie_init,
.destroy = pie_destroy,
.reset = pie_reset,
.change = pie_change,
.dump = pie_dump,
.dump_stats = pie_dump_stats,
.owner = THIS_MODULE,
};
static int __init pie_module_init(void)
{
return register_qdisc(&pie_qdisc_ops);
}
static void __exit pie_module_exit(void)
{
unregister_qdisc(&pie_qdisc_ops);
}
module_init(pie_module_init);
module_exit(pie_module_exit);
MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler");
MODULE_AUTHOR("Vijay Subramanian");
MODULE_AUTHOR("Mythili Prabhu");
MODULE_LICENSE("GPL");
