net/dccp/ccids/lib/loss_interval.c

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