net/dccp/ccids/lib/loss_interval.c

   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 }