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|
/*
* net/sched/sch_choke.c CHOKE scheduler
*
* Copyright (c) 2011 Stephen Hemminger <shemminger@vyatta.com>
* Copyright (c) 2011 Eric Dumazet <eric.dumazet@gmail.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* version 2 as published by the Free Software Foundation.
*
*/
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <linux/vmalloc.h>
#include <net/pkt_sched.h>
#include <net/pkt_cls.h>
#include <net/inet_ecn.h>
#include <net/red.h>
#include <net/flow_dissector.h>
/*
CHOKe stateless AQM for fair bandwidth allocation
=================================================
CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for
unresponsive flows) is a variant of RED that penalizes misbehaving flows but
maintains no flow state. The difference from RED is an additional step
during the enqueuing process. If average queue size is over the
low threshold (qmin), a packet is chosen at random from the queue.
If both the new and chosen packet are from the same flow, both
are dropped. Unlike RED, CHOKe is not really a "classful" qdisc because it
needs to access packets in queue randomly. It has a minimal class
interface to allow overriding the builtin flow classifier with
filters.
Source:
R. Pan, B. Prabhakar, and K. Psounis, "CHOKe, A Stateless
Active Queue Management Scheme for Approximating Fair Bandwidth Allocation",
IEEE INFOCOM, 2000.
A. Tang, J. Wang, S. Low, "Understanding CHOKe: Throughput and Spatial
Characteristics", IEEE/ACM Transactions on Networking, 2004
*/
/* Upper bound on size of sk_buff table (packets) */
#define CHOKE_MAX_QUEUE (128*1024 - 1)
struct choke_sched_data {
/* Parameters */
u32 limit;
unsigned char flags;
struct red_parms parms;
/* Variables */
struct red_vars vars;
struct {
u32 prob_drop; /* Early probability drops */
u32 prob_mark; /* Early probability marks */
u32 forced_drop; /* Forced drops, qavg > max_thresh */
u32 forced_mark; /* Forced marks, qavg > max_thresh */
u32 pdrop; /* Drops due to queue limits */
u32 other; /* Drops due to drop() calls */
u32 matched; /* Drops to flow match */
} stats;
unsigned int head;
unsigned int tail;
unsigned int tab_mask; /* size - 1 */
struct sk_buff **tab;
};
/* number of elements in queue including holes */
static unsigned int choke_len(const struct choke_sched_data *q)
{
return (q->tail - q->head) & q->tab_mask;
}
/* Is ECN parameter configured */
static int use_ecn(const struct choke_sched_data *q)
{
return q->flags & TC_RED_ECN;
}
/* Should packets over max just be dropped (versus marked) */
static int use_harddrop(const struct choke_sched_data *q)
{
return q->flags & TC_RED_HARDDROP;
}
/* Move head pointer forward to skip over holes */
static void choke_zap_head_holes(struct choke_sched_data *q)
{
do {
q->head = (q->head + 1) & q->tab_mask;
if (q->head == q->tail)
break;
} while (q->tab[q->head] == NULL);
}
/* Move tail pointer backwards to reuse holes */
static void choke_zap_tail_holes(struct choke_sched_data *q)
{
do {
q->tail = (q->tail - 1) & q->tab_mask;
if (q->head == q->tail)
break;
} while (q->tab[q->tail] == NULL);
}
/* Drop packet from queue array by creating a "hole" */
static void choke_drop_by_idx(struct Qdisc *sch, unsigned int idx,
struct sk_buff **to_free)
{
struct choke_sched_data *q = qdisc_priv(sch);
struct sk_buff *skb = q->tab[idx];
q->tab[idx] = NULL;
if (idx == q->head)
choke_zap_head_holes(q);
if (idx == q->tail)
choke_zap_tail_holes(q);
qdisc_qstats_backlog_dec(sch, skb);
qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(skb));
qdisc_drop(skb, sch, to_free);
--sch->q.qlen;
}
struct choke_skb_cb {
u16 classid;
u8 keys_valid;
struct flow_keys_digest keys;
};
static inline struct choke_skb_cb *choke_skb_cb(const struct sk_buff *skb)
{
qdisc_cb_private_validate(skb, sizeof(struct choke_skb_cb));
return (struct choke_skb_cb *)qdisc_skb_cb(skb)->data;
}
static inline void choke_set_classid(struct sk_buff *skb, u16 classid)
{
choke_skb_cb(skb)->classid = classid;
}
/*
* Compare flow of two packets
* Returns true only if source and destination address and port match.
* false for special cases
*/
static bool choke_match_flow(struct sk_buff *skb1,
struct sk_buff *skb2)
{
struct flow_keys temp;
if (skb1->protocol != skb2->protocol)
return false;
if (!choke_skb_cb(skb1)->keys_valid) {
choke_skb_cb(skb1)->keys_valid = 1;
skb_flow_dissect_flow_keys(skb1, &temp, 0);
make_flow_keys_digest(&choke_skb_cb(skb1)->keys, &temp);
}
if (!choke_skb_cb(skb2)->keys_valid) {
choke_skb_cb(skb2)->keys_valid = 1;
skb_flow_dissect_flow_keys(skb2, &temp, 0);
make_flow_keys_digest(&choke_skb_cb(skb2)->keys, &temp);
}
return !memcmp(&choke_skb_cb(skb1)->keys,
&choke_skb_cb(skb2)->keys,
sizeof(choke_skb_cb(skb1)->keys));
}
/*
* Select a packet at random from queue
* HACK: since queue can have holes from previous deletion; retry several
* times to find a random skb but then just give up and return the head
* Will return NULL if queue is empty (q->head == q->tail)
*/
static struct sk_buff *choke_peek_random(const struct choke_sched_data *q,
unsigned int *pidx)
{
struct sk_buff *skb;
int retrys = 3;
do {
*pidx = (q->head + prandom_u32_max(choke_len(q))) & q->tab_mask;
skb = q->tab[*pidx];
if (skb)
return skb;
} while (--retrys > 0);
return q->tab[*pidx = q->head];
}
/*
* Compare new packet with random packet in queue
* returns true if matched and sets *pidx
*/
static bool choke_match_random(const struct choke_sched_data *q,
struct sk_buff *nskb,
unsigned int *pidx)
{
struct sk_buff *oskb;
if (q->head == q->tail)
return false;
oskb = choke_peek_random(q, pidx);
return choke_match_flow(oskb, nskb);
}
static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch,
struct sk_buff **to_free)
{
struct choke_sched_data *q = qdisc_priv(sch);
const struct red_parms *p = &q->parms;
choke_skb_cb(skb)->keys_valid = 0;
/* Compute average queue usage (see RED) */
q->vars.qavg = red_calc_qavg(p, &q->vars, sch->q.qlen);
if (red_is_idling(&q->vars))
red_end_of_idle_period(&q->vars);
/* Is queue small? */
if (q->vars.qavg <= p->qth_min)
q->vars.qcount = -1;
else {
unsigned int idx;
/* Draw a packet at random from queue and compare flow */
if (choke_match_random(q, skb, &idx)) {
q->stats.matched++;
choke_drop_by_idx(sch, idx, to_free);
goto congestion_drop;
}
/* Queue is large, always mark/drop */
if (q->vars.qavg > p->qth_max) {
q->vars.qcount = -1;
qdisc_qstats_overlimit(sch);
if (use_harddrop(q) || !use_ecn(q) ||
|