cregit-Linux how code gets into the kernel

Release 4.8 net/sched/sch_sfb.c

Directory: net/sched
/*
 * net/sched/sch_sfb.c    Stochastic Fair Blue
 *
 * Copyright (c) 2008-2011 Juliusz Chroboczek <jch@pps.jussieu.fr>
 * 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.
 *
 * W. Feng, D. Kandlur, D. Saha, K. Shin. Blue:
 * A New Class of Active Queue Management Algorithms.
 * U. Michigan CSE-TR-387-99, April 1999.
 *
 * http://www.thefengs.com/wuchang/blue/CSE-TR-387-99.pdf
 *
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <linux/random.h>
#include <linux/jhash.h>
#include <net/ip.h>
#include <net/pkt_sched.h>
#include <net/inet_ecn.h>

/*
 * SFB uses two B[l][n] : L x N arrays of bins (L levels, N bins per level)
 * This implementation uses L = 8 and N = 16
 * This permits us to split one 32bit hash (provided per packet by rxhash or
 * external classifier) into 8 subhashes of 4 bits.
 */

#define SFB_BUCKET_SHIFT 4

#define SFB_NUMBUCKETS	(1 << SFB_BUCKET_SHIFT) 
/* N bins per Level */

#define SFB_BUCKET_MASK (SFB_NUMBUCKETS - 1)

#define SFB_LEVELS	(32 / SFB_BUCKET_SHIFT) 
/* L */

/* SFB algo uses a virtual queue, named "bin" */

struct sfb_bucket {
	
u16		qlen; /* length of virtual queue */
	
u16		p_mark; /* marking probability */
};

/* We use a double buffering right before hash change
 * (Section 4.4 of SFB reference : moving hash functions)
 */

struct sfb_bins {
	
u32		  perturbation; /* jhash perturbation */
	
struct sfb_bucket bins[SFB_LEVELS][SFB_NUMBUCKETS];
};


struct sfb_sched_data {
	
struct Qdisc	*qdisc;
	
struct tcf_proto __rcu *filter_list;
	
unsigned long	rehash_interval;
	
unsigned long	warmup_time;	/* double buffering warmup time in jiffies */
	
u32		max;
	
u32		bin_size;	/* maximum queue length per bin */
	
u32		increment;	/* d1 */
	
u32		decrement;	/* d2 */
	
u32		limit;		/* HARD maximal queue length */
	
u32		penalty_rate;
	
u32		penalty_burst;
	
u32		tokens_avail;
	
unsigned long	rehash_time;
	
unsigned long	token_time;

	
u8		slot;		/* current active bins (0 or 1) */
	
bool		double_buffering;
	
struct sfb_bins bins[2];

	struct {
		
u32	earlydrop;
		
u32	penaltydrop;
		
u32	bucketdrop;
		
u32	queuedrop;
		
u32	childdrop;	/* drops in child qdisc */
		
u32	marked;		/* ECN mark */
	} 
stats;
};

/*
 * Each queued skb might be hashed on one or two bins
 * We store in skb_cb the two hash values.
 * (A zero value means double buffering was not used)
 */

struct sfb_skb_cb {
	
u32 hashes[2];
};


static inline struct sfb_skb_cb *sfb_skb_cb(const struct sk_buff *skb) { qdisc_cb_private_validate(skb, sizeof(struct sfb_skb_cb)); return (struct sfb_skb_cb *)qdisc_skb_cb(skb)->data; }

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/* * If using 'internal' SFB flow classifier, hash comes from skb rxhash * If using external classifier, hash comes from the classid. */
static u32 sfb_hash(const struct sk_buff *skb, u32 slot) { return sfb_skb_cb(skb)->hashes[slot]; }

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/* Probabilities are coded as Q0.16 fixed-point values, * with 0xFFFF representing 65535/65536 (almost 1.0) * Addition and subtraction are saturating in [0, 65535] */
static u32 prob_plus(u32 p1, u32 p2) { u32 res = p1 + p2; return min_t(u32, res, SFB_MAX_PROB); }

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static u32 prob_minus(u32 p1, u32 p2) { return p1 > p2 ? p1 - p2 : 0; }

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static void increment_one_qlen(u32 sfbhash, u32 slot, struct sfb_sched_data *q) { int i; struct sfb_bucket *b = &q->bins[slot].bins[0][0]; for (i = 0; i < SFB_LEVELS; i++) { u32 hash = sfbhash & SFB_BUCKET_MASK; sfbhash >>= SFB_BUCKET_SHIFT; if (b[hash].qlen < 0xFFFF) b[hash].qlen++; b += SFB_NUMBUCKETS; /* next level */ } }

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static void increment_qlen(const struct sk_buff *skb, struct sfb_sched_data *q) { u32 sfbhash; sfbhash = sfb_hash(skb, 0); if (sfbhash) increment_one_qlen(sfbhash, 0, q); sfbhash = sfb_hash(skb, 1); if (sfbhash) increment_one_qlen(sfbhash, 1, q); }

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static void decrement_one_qlen(u32 sfbhash, u32 slot, struct sfb_sched_data *q) { int i; struct sfb_bucket *b = &q->bins[slot].bins[0][0]; for (i = 0; i < SFB_LEVELS; i++) { u32 hash = sfbhash & SFB_BUCKET_MASK; sfbhash >>= SFB_BUCKET_SHIFT; if (b[hash].qlen > 0) b[hash].qlen--; b += SFB_NUMBUCKETS; /* next level */ } }

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static void decrement_qlen(const struct sk_buff *skb, struct sfb_sched_data *q) { u32 sfbhash; sfbhash = sfb_hash(skb, 0); if (sfbhash) decrement_one_qlen(sfbhash, 0, q); sfbhash = sfb_hash(skb, 1); if (sfbhash) decrement_one_qlen(sfbhash, 1, q); }

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static void decrement_prob(struct sfb_bucket *b, struct sfb_sched_data *q) { b->p_mark = prob_minus(b->p_mark, q->decrement); }

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static void increment_prob(struct sfb_bucket *b, struct sfb_sched_data *q) { b->p_mark = prob_plus(b->p_mark, q->increment); }

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static void sfb_zero_all_buckets(struct sfb_sched_data *q) { memset(&q->bins, 0, sizeof(q->bins)); }

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/* * compute max qlen, max p_mark, and avg p_mark */
static u32 sfb_compute_qlen(u32 *prob_r, u32 *avgpm_r, const struct sfb_sched_data *q) { int i; u32 qlen = 0, prob = 0, totalpm = 0; const struct sfb_bucket *b = &q->bins[q->slot].bins[0][0]; for (i = 0; i < SFB_LEVELS * SFB_NUMBUCKETS; i++) { if (qlen < b->qlen) qlen = b->qlen; totalpm += b->p_mark; if (prob < b->p_mark) prob = b->p_mark; b++; } *prob_r = prob; *avgpm_r = totalpm / (SFB_LEVELS * SFB_NUMBUCKETS); return qlen; }

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static void sfb_init_perturbation(u32 slot, struct sfb_sched_data *q) { q->bins[slot].perturbation = prandom_u32(); }

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static void sfb_swap_slot(struct sfb_sched_data *q) { sfb_init_perturbation(q->slot, q); q->slot ^= 1; q->double_buffering = false; }

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/* Non elastic flows are allowed to use part of the bandwidth, expressed * in "penalty_rate" packets per second, with "penalty_burst" burst */
static bool sfb_rate_limit(struct sk_buff *skb, struct sfb_sched_data *q) { if (q->penalty_rate == 0 || q->penalty_burst == 0) return true; if (q->tokens_avail < 1) { unsigned long age = min(10UL * HZ, jiffies - q->token_time); q->tokens_avail = (age * q->penalty_rate) / HZ; if (q->tokens_avail > q->penalty_burst) q->tokens_avail = q->penalty_burst; q->token_time = jiffies; if (q->tokens_avail < 1) return true; } q->tokens_avail--; return false; }

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static bool sfb_classify(struct sk_buff *skb, struct tcf_proto *fl, int *qerr, u32 *salt) { struct tcf_result res; int result; result = tc_classify(skb, fl, &res, false); if (result >= 0) { #ifdef CONFIG_NET_CLS_ACT switch (result) { case TC_ACT_STOLEN: case TC_ACT_QUEUED: *qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN; case TC_ACT_SHOT: return false; } #endif *salt = TC_H_MIN(res.classid); return true; } return false; }

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static int sfb_enqueue(struct sk_buff *skb, struct Qdisc *sch, struct sk_buff **to_free) { struct sfb_sched_data *q = qdisc_priv(sch); struct Qdisc *child = q->qdisc; struct tcf_proto *fl; int i; u32 p_min = ~0; u32 minqlen = ~0; u32 r, sfbhash; u32 slot = q->slot; int ret = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS; if (unlikely(sch->q.qlen >= q->limit)) { qdisc_qstats_overlimit(sch); q->stats.queuedrop++; goto drop; } if (q->rehash_interval > 0) { unsigned long limit = q->rehash_time + q->rehash_interval; if (unlikely(time_after(jiffies, limit))) { sfb_swap_slot(q); q->rehash_time = jiffies; } else if (unlikely(!q->double_buffering && q->warmup_time > 0 && time_after(jiffies, limit - q->warmup_time))) { q->double_buffering = true; } } fl = rcu_dereference_bh(q->filter_list); if (fl) { u32 salt; /* If using external classifiers, get result and record it. */ if (!sfb_classify(skb, fl, &ret, &salt)) goto other_drop; sfbhash = jhash_1word(salt, q->bins[slot].perturbation); } else { sfbhash = skb_get_hash_perturb(skb, q->bins[slot].perturbation); } if (!sfbhash) sfbhash = 1; sfb_skb_cb(skb)->hashes[slot] = sfbhash; for (i = 0; i < SFB_LEVELS; i++) { u32 hash = sfbhash & SFB_BUCKET_MASK; struct sfb_bucket *b = &q->bins[slot].bins[i][hash]; sfbhash >>= SFB_BUCKET_SHIFT; if (b->qlen == 0) decrement_prob(b, q); else if (b->qlen >= q->bin_size) increment_prob(b, q); if (minqlen > b->qlen) minqlen = b->qlen; if (p_min > b->p_mark) p_min = b->p_mark; } slot ^= 1; sfb_skb_cb(skb)->hashes[slot] = 0; if (unlikely(minqlen >= q->max)) { qdisc_qstats_overlimit(sch); q->stats.bucketdrop++; goto drop; } if (unlikely(p_min >= SFB_MAX_PROB)) { /* Inelastic flow */ if (q->double_buffering) { sfbhash = skb_get_hash_perturb(skb, q->bins[slot].perturbation); if (!sfbhash) sfbhash = 1; sfb_skb_cb(skb)->hashes[slot] = sfbhash; for (i = 0; i < SFB_LEVELS; i++) { u32 hash = sfbhash & SFB_BUCKET_MASK; struct sfb_bucket *b = &q->bins[slot].bins[i][hash]; sfbhash >>= SFB_BUCKET_SHIFT; if (b->qlen == 0) decrement_prob(b, q); else if (b->qlen >= q->bin_size) increment_prob(b, q); } } if (sfb_rate_limit(skb, q)) { qdisc_qstats_overlimit(sch); q->stats.penaltydrop++; goto drop; } goto enqueue; } r = prandom_u32() & SFB_MAX_PROB; if (unlikely(r < p_min)) { if (unlikely(p_min > SFB_MAX_PROB / 2)) { /* If we're marking that many packets, then either * this flow is unresponsive, or we're badly congested. * In either case, we want to start dropping packets. */ if (r < (p_min - SFB_MAX_PROB / 2) * 2) { q->stats.earlydrop++; goto drop; } } if (INET_ECN_set_ce(skb)) { q->stats.marked++; } else { q->stats.earlydrop++; goto drop; } } enqueue: ret = qdisc_enqueue(skb, child, to_free); if (likely(ret == NET_XMIT_SUCCESS)) { qdisc_qstats_backlog_inc(sch, skb); sch->q.qlen++; increment_qlen(skb, q); } else if (net_xmit_drop_count(ret)) { q->stats.childdrop++; qdisc_qstats_drop(sch); } return ret; drop: qdisc_drop(skb, sch, to_free); return NET_XMIT_CN; other_drop: if (ret & __NET_XMIT_BYPASS) qdisc_qstats_drop(sch); kfree_skb(skb); return ret; }

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static struct sk_buff *sfb_dequeue(struct Qdisc *sch) { struct sfb_sched_data *q = qdisc_priv(sch); struct Qdisc *child = q->qdisc; struct sk_buff *skb; skb = child->dequeue(q->qdisc); if (skb) { qdisc_bstats_update(sch, skb); qdisc_qstats_backlog_dec(sch, skb); sch->q.qlen--; decrement_qlen(skb, q); } return skb; }

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static struct sk_buff *sfb_peek(struct Qdisc *sch) { struct sfb_sched_data *q = qdisc_priv(sch); struct Qdisc *child = q->qdisc; return child->ops->peek(child); }

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/* No sfb_drop -- impossible since the child doesn't return the dropped skb. */
static void sfb_reset(struct Qdisc *sch) { struct sfb_sched_data *q = qdisc_priv(sch); qdisc_reset(q->qdisc); sch->qstats.backlog = 0; sch->q.qlen = 0; q->slot = 0; q->double_buffering = false; sfb_zero_all_buckets(q); sfb_init_perturbation(0, q); }

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static void sfb_destroy(struct Qdisc *sch) { struct sfb_sched_data *q = qdisc_priv(sch); tcf_destroy_chain(&q->filter_list); qdisc_destroy(q->qdisc); }

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static const struct nla_policy sfb_policy[TCA_SFB_MAX + 1] = { [TCA_SFB_PARMS] = { .len = sizeof(struct tc_sfb_qopt) }, }; static const struct tc_sfb_qopt sfb_default_ops = { .rehash_interval = 600 * MSEC_PER_SEC, .warmup_time = 60 * MSEC_PER_SEC, .limit = 0, .max = 25, .bin_size = 20, .increment = (SFB_MAX_PROB + 500) / 1000, /* 0.1 % */ .decrement = (SFB_MAX_PROB + 3000) / 6000, .penalty_rate = 10, .penalty_burst = 20, };
static int sfb_change(struct Qdisc *sch, struct nlattr *opt) { struct sfb_sched_data *q = qdisc_priv(sch); struct Qdisc *child; struct nlattr *tb[TCA_SFB_MAX + 1]; const struct tc_sfb_qopt *ctl = &sfb_default_ops; u32 limit; int err; if (opt) { err = nla_parse_nested(tb, TCA_SFB_MAX, opt, sfb_policy); if (err < 0) return -EINVAL; if (tb[TCA_SFB_PARMS] == NULL) return -EINVAL; ctl = nla_data(tb[TCA_SFB_PARMS]); } limit = ctl->limit; if (limit == 0) limit = qdisc_dev(sch)->tx_queue_len; child = fifo_create_dflt(sch, &pfifo_qdisc_ops, limit); if (IS_ERR(child)) return PTR_ERR(child); sch_tree_lock(sch); qdisc_tree_reduce_backlog(q->qdisc, q->qdisc->q.qlen, q->qdisc->qstats.backlog); qdisc_destroy(q->qdisc); q->qdisc = child; q->rehash_interval = msecs_to_jiffies(ctl->rehash_interval); q->warmup_time = msecs_to_jiffies(ctl->warmup_time); q->rehash_time = jiffies; q->limit = limit; q->increment = ctl->increment; q->decrement = ctl->decrement; q->max = ctl->max; q->bin_size = ctl->bin_size; q->penalty_rate = ctl->penalty_rate; q->penalty_burst = ctl->penalty_burst; q->tokens_avail = ctl->penalty_burst; q->token_time = jiffies; q->slot = 0; q->double_buffering = false; sfb_zero_all_buckets(q); sfb_init_perturbation(0, q); sfb_init_perturbation(1, q); sch_tree_unlock(sch); return 0; }

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static int sfb_init(struct Qdisc *sch, struct nlattr *opt) { struct sfb_sched_data *q = qdisc_priv(sch); q->qdisc = &noop_qdisc; return sfb_change(sch, opt); }

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static int sfb_dump(struct Qdisc *sch, struct sk_buff *skb) { struct sfb_sched_data *q = qdisc_priv(sch); struct nlattr *opts; struct tc_sfb_qopt opt = { .rehash_interval = jiffies_to_msecs(q->rehash_interval), .warmup_time = jiffies_to_msecs(q->warmup_time), .limit = q->limit, .max = q->max, .bin_size = q->bin_size, .increment = q->increment, .decrement = q->decrement, .penalty_rate = q->penalty_rate, .penalty_burst = q->penalty_burst, }; sch->qstats.backlog = q->qdisc->qstats.backlog; opts = nla_nest_start(skb, TCA_OPTIONS); if (opts == NULL) goto nla_put_failure; if (nla_put(skb, TCA_SFB_PARMS, sizeof(opt), &opt)) goto nla_put_failure; return nla_nest_end(skb, opts); nla_put_failure: nla_nest_cancel(skb, opts); return -EMSGSIZE; }

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static int sfb_dump_stats(struct Qdisc *sch, struct gnet_dump *d) { struct sfb_sched_data *q = qdisc_priv(sch); struct tc_sfb_xstats st = { .earlydrop = q->stats.earlydrop, .penaltydrop = q->stats.penaltydrop, .bucketdrop = q->stats.bucketdrop, .queuedrop = q->stats.queuedrop, .childdrop = q->stats.childdrop, .marked = q->stats.marked, }; st.maxqlen = sfb_compute_qlen(&st.maxprob, &st.avgprob, q); return gnet_stats_copy_app(d, &st, sizeof(st)); }

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static int sfb_dump_class(struct Qdisc *sch, unsigned long cl, struct sk_buff *skb, struct tcmsg *tcm) { return -ENOSYS; }

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static int sfb_graft(struct Qdisc *sch, unsigned long arg, struct Qdisc *new, struct Qdisc **old) { struct sfb_sched_data *q = qdisc_priv(sch); if (new == NULL) new = &noop_qdisc; *old = qdisc_replace(sch, new, &q->qdisc); return 0; }

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static struct Qdisc *sfb_leaf(struct Qdisc *sch, unsigned long arg) { struct sfb_sched_data *q = qdisc_priv(sch); return q->qdisc; }

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static unsigned long