loss_interval.c

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/*
 *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
 *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
 *  Copyright (c) 2005-7 Ian McDonald <[email protected]>
 *  Copyright (c) 2005 Arnaldo Carvalho de Melo <[email protected]>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 */
#include <net/sock.h>
#include "tfrc.h"

static struct kmem_cache  *tfrc_lh_slab  __read_mostly;
/* Loss Interval weights from [RFC 3448, 5.4], scaled by 10 */
static const int tfrc_lh_weights[NINTERVAL] = { 10, 10, 10, 10, 8, 6, 4, 2 };

/* implements LIFO semantics on the array */
static inline u8 LIH_INDEX(const u8 ctr)
{
    return LIH_SIZE - 1 - (ctr % LIH_SIZE);
}

/* the `counter' index always points at the next entry to be populated */
static inline struct tfrc_loss_interval *tfrc_lh_peek(struct tfrc_loss_hist *lh)
{
    return lh->counter ? lh->ring[LIH_INDEX(lh->counter - 1)] : NULL;
}

/* given i with 0 <= i <= k, return I_i as per the rfc3448bis notation */
static inline u32 tfrc_lh_get_interval(struct tfrc_loss_hist *lh, const u8 i)
{
    BUG_ON(i >= lh->counter);
    return lh->ring[LIH_INDEX(lh->counter - i - 1)]->li_length;
}

/*
 *  On-demand allocation and de-allocation of entries
 */
static struct tfrc_loss_interval *tfrc_lh_demand_next(struct tfrc_loss_hist *lh)
{
    if (lh->ring[LIH_INDEX(lh->counter)] == NULL)
        lh->ring[LIH_INDEX(lh->counter)] = kmem_cache_alloc(tfrc_lh_slab,
                                    GFP_ATOMIC);
    return lh->ring[LIH_INDEX(lh->counter)];
}

void tfrc_lh_cleanup(struct tfrc_loss_hist *lh)
{
    if (!tfrc_lh_is_initialised(lh))
        return;

    for (lh->counter = 0; lh->counter < LIH_SIZE; lh->counter++)
        if (lh->ring[LIH_INDEX(lh->counter)] != NULL) {
            kmem_cache_free(tfrc_lh_slab,
                    lh->ring[LIH_INDEX(lh->counter)]);
            lh->ring[LIH_INDEX(lh->counter)] = NULL;
        }
}

static void tfrc_lh_calc_i_mean(struct tfrc_loss_hist *lh)
{
    u32 i_i, i_tot0 = 0, i_tot1 = 0, w_tot = 0;
    int i, k = tfrc_lh_length(lh) - 1; /* k is as in rfc3448bis, 5.4 */

    if (k <= 0)
        return;

    for (i = 0; i <= k; i++) {
        i_i = tfrc_lh_get_interval(lh, i);

        if (i < k) {
            i_tot0 += i_i * tfrc_lh_weights[i];
            w_tot  += tfrc_lh_weights[i];
        }
        if (i > 0)
            i_tot1 += i_i * tfrc_lh_weights[i-1];
    }

    lh->i_mean = max(i_tot0, i_tot1) / w_tot;
}

u8 tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *skb)
{
    struct tfrc_loss_interval *cur = tfrc_lh_peek(lh);
    u32 old_i_mean = lh->i_mean;
    s64 len;

    if (cur == NULL)            /* not initialised */
        return 0;

    len = dccp_delta_seqno(cur->li_seqno, DCCP_SKB_CB(skb)->dccpd_seq) + 1;

    if (len - (s64)cur->li_length <= 0) /* duplicate or reordered */
        return 0;

    if (SUB16(dccp_hdr(skb)->dccph_ccval, cur->li_ccval) > 4)
        /*
         * Implements RFC 4342, 10.2:
         * If a packet S (skb) exists whose seqno comes `after' the one
         * starting the current loss interval (cur) and if the modulo-16
         * distance from C(cur) to C(S) is greater than 4, consider all
         * subsequent packets as belonging to a new loss interval. This
         * test is necessary since CCVal may wrap between intervals.
         */
        cur->li_is_closed = 1;

    if (tfrc_lh_length(lh) == 1)        /* due to RFC 3448, 6.3.1 */
        return 0;

    cur->li_length = len;
    tfrc_lh_calc_i_mean(lh);

    return lh->i_mean < old_i_mean;
}

/* Determine if `new_loss' does begin a new loss interval [RFC 4342, 10.2] */
static inline u8 tfrc_lh_is_new_loss(struct tfrc_loss_interval *cur,
                     struct tfrc_rx_hist_entry *new_loss)
{
    return  dccp_delta_seqno(cur->li_seqno, new_loss->tfrchrx_seqno) > 0 &&
        (cur->li_is_closed || SUB16(new_loss->tfrchrx_ccval, cur->li_ccval) > 4);
}

int tfrc_lh_interval_add(struct tfrc_loss_hist *lh, struct tfrc_rx_hist *rh,
             u32 (*calc_first_li)(struct sock *), struct sock *sk)
{
    struct tfrc_loss_interval *cur = tfrc_lh_peek(lh), *new;

    if (cur != NULL && !tfrc_lh_is_new_loss(cur, tfrc_rx_hist_loss_prev(rh)))
        return 0;

    new = tfrc_lh_demand_next(lh);
    if (unlikely(new == NULL)) {
        DCCP_CRIT("Cannot allocate/add loss record.");
        return 0;
    }

    new->li_seqno     = tfrc_rx_hist_loss_prev(rh)->tfrchrx_seqno;
    new->li_ccval     = tfrc_rx_hist_loss_prev(rh)->tfrchrx_ccval;
    new->li_is_closed = 0;

    if (++lh->counter == 1)
        lh->i_mean = new->li_length = (*calc_first_li)(sk);
    else {
        cur->li_length = dccp_delta_seqno(cur->li_seqno, new->li_seqno);
        new->li_length = dccp_delta_seqno(new->li_seqno,
                  tfrc_rx_hist_last_rcv(rh)->tfrchrx_seqno) + 1;
        if (lh->counter > (2*LIH_SIZE))
            lh->counter -= LIH_SIZE;

        tfrc_lh_calc_i_mean(lh);
    }
    return 1;
}

int __init tfrc_li_init(void)
{
    tfrc_lh_slab = kmem_cache_create("tfrc_li_hist",
                     sizeof(struct tfrc_loss_interval), 0,
                     SLAB_HWCACHE_ALIGN, NULL);
    return tfrc_lh_slab == NULL ? -ENOBUFS : 0;
}

void tfrc_li_exit(void)
{
    if (tfrc_lh_slab != NULL) {
        kmem_cache_destroy(tfrc_lh_slab);
        tfrc_lh_slab = NULL;
    }
}