net/dccp/ccids/lib/loss_interval.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
   4  *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
   5  *  Copyright (c) 2005-7 Ian McDonald <ian.mcdonald@jandi.co.nz>
   6  *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
   7  */
   8 #include <net/sock.h>
   9 #include "tfrc.h"
  10
  11 static struct kmem_cache  *tfrc_lh_slab  __read_mostly;
  12 /* Loss Interval weights from [RFC 3448, 5.4], scaled by 10 */
  13 static const int tfrc_lh_weights[NINTERVAL] = { 10, 10, 10, 10, 8, 6, 4, 2 };
  14
  15 /* implements LIFO semantics on the array */
  16 static inline u8 LIH_INDEX(const u8 ctr)
  17 {
  18         return LIH_SIZE - 1 - (ctr % LIH_SIZE);
  19 }
  20
  21 /* the `counter' index always points at the next entry to be populated */
  22 static inline struct tfrc_loss_interval *tfrc_lh_peek(struct tfrc_loss_hist *lh)
  23 {
  24         return lh->counter ? lh->ring[LIH_INDEX(lh->counter - 1)] : NULL;
  25 }
  26
  27 /* given i with 0 <= i <= k, return I_i as per the rfc3448bis notation */
  28 static inline u32 tfrc_lh_get_interval(struct tfrc_loss_hist *lh, const u8 i)
  29 {
  30         BUG_ON(i >= lh->counter);
  31         return lh->ring[LIH_INDEX(lh->counter - i - 1)]->li_length;
  32 }
  33
  34 /*
  35  *      On-demand allocation and de-allocation of entries
  36  */
  37 static struct tfrc_loss_interval *tfrc_lh_demand_next(struct tfrc_loss_hist *lh)
  38 {
  39         if (lh->ring[LIH_INDEX(lh->counter)] == NULL)
  40                 lh->ring[LIH_INDEX(lh->counter)] = kmem_cache_alloc(tfrc_lh_slab,
  41                                                                     GFP_ATOMIC);
  42         return lh->ring[LIH_INDEX(lh->counter)];
  43 }
  44
  45 void tfrc_lh_cleanup(struct tfrc_loss_hist *lh)
  46 {
  47         if (!tfrc_lh_is_initialised(lh))
  48                 return;
  49
  50         for (lh->counter = 0; lh->counter < LIH_SIZE; lh->counter++)
  51                 if (lh->ring[LIH_INDEX(lh->counter)] != NULL) {
  52                         kmem_cache_free(tfrc_lh_slab,
  53                                         lh->ring[LIH_INDEX(lh->counter)]);
  54                         lh->ring[LIH_INDEX(lh->counter)] = NULL;
  55                 }
  56 }
  57
  58 static void tfrc_lh_calc_i_mean(struct tfrc_loss_hist *lh)
  59 {
  60         u32 i_i, i_tot0 = 0, i_tot1 = 0, w_tot = 0;
  61         int i, k = tfrc_lh_length(lh) - 1; /* k is as in rfc3448bis, 5.4 */
  62
  63         if (k <= 0)
  64                 return;
  65
  66         for (i = 0; i <= k; i++) {
  67                 i_i = tfrc_lh_get_interval(lh, i);
  68
  69                 if (i < k) {
  70                         i_tot0 += i_i * tfrc_lh_weights[i];
  71                         w_tot  += tfrc_lh_weights[i];
  72                 }
  73                 if (i > 0)
  74                         i_tot1 += i_i * tfrc_lh_weights[i-1];
  75         }
  76
  77         lh->i_mean = max(i_tot0, i_tot1) / w_tot;
  78 }
  79
  80 /**
  81  * tfrc_lh_update_i_mean  -  Update the `open' loss interval I_0
  82  * @lh: histogram to update
  83  * @skb: received socket triggering loss interval update
  84  *
  85  * For recomputing p: returns `true' if p > p_prev  <=>  1/p < 1/p_prev
  86  */
  87 u8 tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *skb)
  88 {
  89         struct tfrc_loss_interval *cur = tfrc_lh_peek(lh);
  90         u32 old_i_mean = lh->i_mean;
  91         s64 len;
  92
  93         if (cur == NULL)                        /* not initialised */
  94                 return 0;
  95
  96         len = dccp_delta_seqno(cur->li_seqno, DCCP_SKB_CB(skb)->dccpd_seq) + 1;
  97
  98         if (len - (s64)cur->li_length <= 0)     /* duplicate or reordered */
  99                 return 0;
 100
 101         if (SUB16(dccp_hdr(skb)->dccph_ccval, cur->li_ccval) > 4)
 102                 /*
 103                  * Implements RFC 4342, 10.2:
 104                  * If a packet S (skb) exists whose seqno comes `after' the one
 105                  * starting the current loss interval (cur) and if the modulo-16
 106                  * distance from C(cur) to C(S) is greater than 4, consider all
 107                  * subsequent packets as belonging to a new loss interval. This
 108                  * test is necessary since CCVal may wrap between intervals.
 109                  */
 110                 cur->li_is_closed = 1;
 111
 112         if (tfrc_lh_length(lh) == 1)            /* due to RFC 3448, 6.3.1 */
 113                 return 0;
 114
 115         cur->li_length = len;
 116         tfrc_lh_calc_i_mean(lh);
 117
 118         return lh->i_mean < old_i_mean;
 119 }
 120
 121 /* Determine if `new_loss' does begin a new loss interval [RFC 4342, 10.2] */
 122 static inline u8 tfrc_lh_is_new_loss(struct tfrc_loss_interval *cur,
 123                                      struct tfrc_rx_hist_entry *new_loss)
 124 {
 125         return  dccp_delta_seqno(cur->li_seqno, new_loss->tfrchrx_seqno) > 0 &&
 126                 (cur->li_is_closed || SUB16(new_loss->tfrchrx_ccval, cur->li_ccval) > 4);
 127 }
 128
 129 /**
 130  * tfrc_lh_interval_add  -  Insert new record into the Loss Interval database
 131  * @lh:            Loss Interval database
 132  * @rh:            Receive history containing a fresh loss event
 133  * @calc_first_li: Caller-dependent routine to compute length of first interval
 134  * @sk:            Used by @calc_first_li in caller-specific way (subtyping)
 135  *
 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 }