xref: /openbmc/linux/net/dccp/ccids/lib/loss_interval.c (revision 22246614)
1 /*
2  *  net/dccp/ccids/lib/loss_interval.c
3  *
4  *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
5  *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
6  *  Copyright (c) 2005-7 Ian McDonald <ian.mcdonald@jandi.co.nz>
7  *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
8  *
9  *  This program is free software; you can redistribute it and/or modify
10  *  it under the terms of the GNU General Public License as published by
11  *  the Free Software Foundation; either version 2 of the License, or
12  *  (at your option) any later version.
13  */
14 #include <net/sock.h>
15 #include "tfrc.h"
16 
17 static struct kmem_cache  *tfrc_lh_slab  __read_mostly;
18 /* Loss Interval weights from [RFC 3448, 5.4], scaled by 10 */
19 static const int tfrc_lh_weights[NINTERVAL] = { 10, 10, 10, 10, 8, 6, 4, 2 };
20 
21 /* implements LIFO semantics on the array */
22 static inline u8 LIH_INDEX(const u8 ctr)
23 {
24 	return (LIH_SIZE - 1 - (ctr % LIH_SIZE));
25 }
26 
27 /* the `counter' index always points at the next entry to be populated */
28 static inline struct tfrc_loss_interval *tfrc_lh_peek(struct tfrc_loss_hist *lh)
29 {
30 	return lh->counter ? lh->ring[LIH_INDEX(lh->counter - 1)] : NULL;
31 }
32 
33 /* given i with 0 <= i <= k, return I_i as per the rfc3448bis notation */
34 static inline u32 tfrc_lh_get_interval(struct tfrc_loss_hist *lh, const u8 i)
35 {
36 	BUG_ON(i >= lh->counter);
37 	return lh->ring[LIH_INDEX(lh->counter - i - 1)]->li_length;
38 }
39 
40 /*
41  *	On-demand allocation and de-allocation of entries
42  */
43 static struct tfrc_loss_interval *tfrc_lh_demand_next(struct tfrc_loss_hist *lh)
44 {
45 	if (lh->ring[LIH_INDEX(lh->counter)] == NULL)
46 		lh->ring[LIH_INDEX(lh->counter)] = kmem_cache_alloc(tfrc_lh_slab,
47 								    GFP_ATOMIC);
48 	return lh->ring[LIH_INDEX(lh->counter)];
49 }
50 
51 void tfrc_lh_cleanup(struct tfrc_loss_hist *lh)
52 {
53 	if (!tfrc_lh_is_initialised(lh))
54 		return;
55 
56 	for (lh->counter = 0; lh->counter < LIH_SIZE; lh->counter++)
57 		if (lh->ring[LIH_INDEX(lh->counter)] != NULL) {
58 			kmem_cache_free(tfrc_lh_slab,
59 					lh->ring[LIH_INDEX(lh->counter)]);
60 			lh->ring[LIH_INDEX(lh->counter)] = NULL;
61 		}
62 }
63 EXPORT_SYMBOL_GPL(tfrc_lh_cleanup);
64 
65 static void tfrc_lh_calc_i_mean(struct tfrc_loss_hist *lh)
66 {
67 	u32 i_i, i_tot0 = 0, i_tot1 = 0, w_tot = 0;
68 	int i, k = tfrc_lh_length(lh) - 1; /* k is as in rfc3448bis, 5.4 */
69 
70 	for (i=0; i <= k; i++) {
71 		i_i = tfrc_lh_get_interval(lh, i);
72 
73 		if (i < k) {
74 			i_tot0 += i_i * tfrc_lh_weights[i];
75 			w_tot  += tfrc_lh_weights[i];
76 		}
77 		if (i > 0)
78 			i_tot1 += i_i * tfrc_lh_weights[i-1];
79 	}
80 
81 	BUG_ON(w_tot == 0);
82 	lh->i_mean = max(i_tot0, i_tot1) / w_tot;
83 }
84 
85 /**
86  * tfrc_lh_update_i_mean  -  Update the `open' loss interval I_0
87  * For recomputing p: returns `true' if p > p_prev  <=>  1/p < 1/p_prev
88  */
89 u8 tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *skb)
90 {
91 	struct tfrc_loss_interval *cur = tfrc_lh_peek(lh);
92 	u32 old_i_mean = lh->i_mean;
93 	s64 length;
94 
95 	if (cur == NULL)			/* not initialised */
96 		return 0;
97 
98 	length = dccp_delta_seqno(cur->li_seqno, DCCP_SKB_CB(skb)->dccpd_seq);
99 
100 	if (length - cur->li_length <= 0)	/* duplicate or reordered */
101 		return 0;
102 
103 	if (SUB16(dccp_hdr(skb)->dccph_ccval, cur->li_ccval) > 4)
104 		/*
105 		 * Implements RFC 4342, 10.2:
106 		 * If a packet S (skb) exists whose seqno comes `after' the one
107 		 * starting the current loss interval (cur) and if the modulo-16
108 		 * distance from C(cur) to C(S) is greater than 4, consider all
109 		 * subsequent packets as belonging to a new loss interval. This
110 		 * test is necessary since CCVal may wrap between intervals.
111 		 */
112 		cur->li_is_closed = 1;
113 
114 	if (tfrc_lh_length(lh) == 1)		/* due to RFC 3448, 6.3.1 */
115 		return 0;
116 
117 	cur->li_length = length;
118 	tfrc_lh_calc_i_mean(lh);
119 
120 	return (lh->i_mean < old_i_mean);
121 }
122 EXPORT_SYMBOL_GPL(tfrc_lh_update_i_mean);
123 
124 /* Determine if `new_loss' does begin a new loss interval [RFC 4342, 10.2] */
125 static inline u8 tfrc_lh_is_new_loss(struct tfrc_loss_interval *cur,
126 				     struct tfrc_rx_hist_entry *new_loss)
127 {
128 	return	dccp_delta_seqno(cur->li_seqno, new_loss->tfrchrx_seqno) > 0 &&
129 		(cur->li_is_closed || SUB16(new_loss->tfrchrx_ccval, cur->li_ccval) > 4);
130 }
131 
132 /** tfrc_lh_interval_add  -  Insert new record into the Loss Interval database
133  * @lh:		   Loss Interval database
134  * @rh:		   Receive history containing a fresh loss event
135  * @calc_first_li: Caller-dependent routine to compute length of first interval
136  * @sk:		   Used by @calc_first_li in caller-specific way (subtyping)
137  * Updates I_mean and returns 1 if a new interval has in fact been added to @lh.
138  */
139 int tfrc_lh_interval_add(struct tfrc_loss_hist *lh, struct tfrc_rx_hist *rh,
140 			 u32 (*calc_first_li)(struct sock *), struct sock *sk)
141 {
142 	struct tfrc_loss_interval *cur = tfrc_lh_peek(lh), *new;
143 
144 	if (cur != NULL && !tfrc_lh_is_new_loss(cur, tfrc_rx_hist_loss_prev(rh)))
145 		return 0;
146 
147 	new = tfrc_lh_demand_next(lh);
148 	if (unlikely(new == NULL)) {
149 		DCCP_CRIT("Cannot allocate/add loss record.");
150 		return 0;
151 	}
152 
153 	new->li_seqno	  = tfrc_rx_hist_loss_prev(rh)->tfrchrx_seqno;
154 	new->li_ccval	  = tfrc_rx_hist_loss_prev(rh)->tfrchrx_ccval;
155 	new->li_is_closed = 0;
156 
157 	if (++lh->counter == 1)
158 		lh->i_mean = new->li_length = (*calc_first_li)(sk);
159 	else {
160 		cur->li_length = dccp_delta_seqno(cur->li_seqno, new->li_seqno);
161 		new->li_length = dccp_delta_seqno(new->li_seqno,
162 				  tfrc_rx_hist_last_rcv(rh)->tfrchrx_seqno);
163 		if (lh->counter > (2*LIH_SIZE))
164 			lh->counter -= LIH_SIZE;
165 
166 		tfrc_lh_calc_i_mean(lh);
167 	}
168 	return 1;
169 }
170 EXPORT_SYMBOL_GPL(tfrc_lh_interval_add);
171 
172 int __init tfrc_li_init(void)
173 {
174 	tfrc_lh_slab = kmem_cache_create("tfrc_li_hist",
175 					 sizeof(struct tfrc_loss_interval), 0,
176 					 SLAB_HWCACHE_ALIGN, NULL);
177 	return tfrc_lh_slab == NULL ? -ENOBUFS : 0;
178 }
179 
180 void tfrc_li_exit(void)
181 {
182 	if (tfrc_lh_slab != NULL) {
183 		kmem_cache_destroy(tfrc_lh_slab);
184 		tfrc_lh_slab = NULL;
185 	}
186 }
187