tcp_bt.c

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/*
 * Copyright (c) 2019 Cisco and/or its affiliates.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at:
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * TCP byte tracker that can generate delivery rate estimates. Based on
 * draft-cheng-iccrg-delivery-rate-estimation-00
 */

#include <vnet/tcp/tcp.h>

static tcp_bt_sample_t *
bt_get_sample (tcp_byte_tracker_t * bt, u32 bts_index)
{
  if (pool_is_free_index (bt->samples, bts_index))
    return 0;
  return pool_elt_at_index (bt->samples, bts_index);
}

static tcp_bt_sample_t *
bt_next_sample (tcp_byte_tracker_t * bt, tcp_bt_sample_t * bts)
{
  return bt_get_sample (bt, bts->next);
}

static tcp_bt_sample_t *
bt_prev_sample (tcp_byte_tracker_t * bt, tcp_bt_sample_t * bts)
{
  return bt_get_sample (bt, bts->prev);
}

static u32
bt_sample_index (tcp_byte_tracker_t * bt, tcp_bt_sample_t * bts)
{
  if (!bts)
    return TCP_BTS_INVALID_INDEX;
  return bts - bt->samples;
}

static inline int
bt_seq_lt (u32 a, u32 b)
{
  return seq_lt (a, b);
}

static tcp_bt_sample_t *
bt_alloc_sample (tcp_byte_tracker_t * bt, u32 min_seq)
{
  tcp_bt_sample_t *bts;

  pool_get_zero (bt->samples, bts);
  bts->next = bts->prev = TCP_BTS_INVALID_INDEX;
  bts->min_seq = min_seq;
  rb_tree_add_custom (&bt->sample_lookup, bts->min_seq, bts - bt->samples,
                      bt_seq_lt);
  return bts;
}

static void
bt_free_sample (tcp_byte_tracker_t * bt, tcp_bt_sample_t * bts)
{
  if (bts->prev != TCP_BTS_INVALID_INDEX)
    {
      tcp_bt_sample_t *prev = bt_prev_sample (bt, bts);
      prev->next = bts->next;
    }
  else
    bt->head = bts->next;

  if (bts->next != TCP_BTS_INVALID_INDEX)
    {
      tcp_bt_sample_t *next = bt_next_sample (bt, bts);
      next->prev = bts->prev;
    }
  else
    bt->tail = bts->prev;

  rb_tree_del_custom (&bt->sample_lookup, bts->min_seq, bt_seq_lt);
  if (CLIB_DEBUG)
    memset (bts, 0xfc, sizeof (*bts));
  pool_put (bt->samples, bts);
}

static tcp_bt_sample_t *
bt_lookup_seq (tcp_byte_tracker_t * bt, u32 seq)
{
  rb_tree_t *rt = &bt->sample_lookup;
  rb_node_t *cur, *prev;
  tcp_bt_sample_t *bts;

  cur = rb_node (rt, rt->root);
  if (rb_node_is_tnil (rt, cur))
    return 0;

  while (seq != cur->key)
    {
      prev = cur;
      if (seq_lt (seq, cur->key))
        cur = rb_node_left (rt, cur);
      else
        cur = rb_node_right (rt, cur);

      if (rb_node_is_tnil (rt, cur))
        {
          /* Hit tnil as a left child. Find predecessor */
          if (seq_lt (seq, prev->key))
            {
              cur = rb_tree_predecessor (rt, prev);
              if (rb_node_is_tnil (rt, cur))
                return 0;
              bts = bt_get_sample (bt, cur->opaque);
            }
          /* Hit tnil as a right child */
          else
            {
              bts = bt_get_sample (bt, prev->opaque);
            }

          if (seq_geq (seq, bts->min_seq))
            return bts;

          return 0;
        }
    }

  if (!rb_node_is_tnil (rt, cur))
    return bt_get_sample (bt, cur->opaque);

  return 0;
}

static void
bt_update_sample (tcp_byte_tracker_t * bt, tcp_bt_sample_t * bts, u32 seq)
{
  rb_tree_del_custom (&bt->sample_lookup, bts->min_seq, bt_seq_lt);
  bts->min_seq = seq;
  rb_tree_add_custom (&bt->sample_lookup, bts->min_seq,
                      bt_sample_index (bt, bts), bt_seq_lt);
}

static tcp_bt_sample_t *
bt_fix_overlapped (tcp_byte_tracker_t * bt, tcp_bt_sample_t * start,
                   u32 seq, u8 is_end)
{
  tcp_bt_sample_t *cur, *next;

  cur = start;
  while ((next = bt_next_sample (bt, cur)) && seq_lt (next->min_seq, seq))
    {
      bt_free_sample (bt, cur);
      cur = next;
    }

  if (next)
    {
      bt_free_sample (bt, cur);
      return next;
    }

  /* Overlapping current entirely */
  if (is_end)
    {
      bt_free_sample (bt, cur);
      return 0;
    }

  /* Overlapping head of current but not all */
  bt_update_sample (bt, cur, seq);
  return cur;
}

int
tcp_bt_is_sane (tcp_byte_tracker_t * bt)
{
  tcp_bt_sample_t *bts, *tmp;

  if (pool_elts (bt->samples) != pool_elts (bt->sample_lookup.nodes) - 1)
    return 0;

  if (bt->head == TCP_BTS_INVALID_INDEX)
    {
      if (bt->tail != TCP_BTS_INVALID_INDEX)
        return 0;
      if (pool_elts (bt->samples) != 0)
        return 0;
      return 1;
    }

  bts = bt_get_sample (bt, bt->tail);
  if (!bts)
    return 0;

  bts = bt_get_sample (bt, bt->head);
  if (!bts || bts->prev != TCP_BTS_INVALID_INDEX)
    return 0;

  while (bts)
    {
      tmp = bt_lookup_seq (bt, bts->min_seq);
      if (!tmp)
        return 0;
      if (tmp != bts)
        return 0;
      tmp = bt_next_sample (bt, bts);
      if (tmp)
        {
          if (tmp->prev != bt_sample_index (bt, bts))
            {
              clib_warning ("next %u thinks prev is %u should be %u",
                            bts->next, tmp->prev, bt_sample_index (bt, bts));
              return 0;
            }
          if (!seq_lt (bts->min_seq, tmp->min_seq))
            return 0;
        }
      else
        {
          if (bt->tail != bt_sample_index (bt, bts))
            return 0;
          if (bts->next != TCP_BTS_INVALID_INDEX)
            return 0;
        }
      bts = tmp;
    }
  return 1;
}

static tcp_bt_sample_t *
tcp_bt_alloc_tx_sample (tcp_connection_t * tc, u32 min_seq)
{
  tcp_bt_sample_t *bts;
  bts = bt_alloc_sample (tc->bt, min_seq);
  bts->delivered = tc->delivered;
  bts->delivered_time = tc->delivered_time;
  bts->tx_rate = transport_connection_tx_pacer_rate (&tc->connection);
  bts->tx_time = tcp_time_now_us (tc->c_thread_index);
  bts->flags |= tc->app_limited ? TCP_BTS_IS_APP_LIMITED : 0;
  return bts;
}

void
tcp_bt_check_app_limited (tcp_connection_t * tc)
{
  u32 available_bytes, flight_size;

  available_bytes = transport_max_tx_dequeue (&tc->connection);
  flight_size = tcp_flight_size (tc);

  /* Not enough bytes to fill the cwnd */
  if (available_bytes + flight_size + tc->snd_mss < tc->cwnd
      /* Bytes considered lost have been retransmitted */
      && tc->sack_sb.lost_bytes <= tc->snd_rxt_bytes)
    tc->app_limited = tc->delivered + flight_size ? : 1;
}

void
tcp_bt_track_tx (tcp_connection_t * tc)
{
  tcp_byte_tracker_t *bt = tc->bt;
  tcp_bt_sample_t *bts, *tail;
  u32 bts_index;

  if (tc->snd_una == tc->snd_nxt)
    tc->delivered_time = tcp_time_now_us (tc->c_thread_index);

  bts = tcp_bt_alloc_tx_sample (tc, tc->snd_nxt);
  bts_index = bt_sample_index (bt, bts);
  tail = bt_get_sample (bt, bt->tail);
  if (tail)
    {
      tail->next = bts_index;
      bts->prev = bt->tail;
      bt->tail = bts_index;
    }
  else
    {
      bt->tail = bt->head = bts_index;
    }
}

void
tcp_bt_track_rxt (tcp_connection_t * tc, u32 start, u32 end)
{
  tcp_byte_tracker_t *bt = tc->bt;
  tcp_bt_sample_t *bts, *next, *cur, *prev, *nbts;
  u32 bts_index, cur_index, next_index, prev_index, min_seq;
  u8 is_end = end == tc->snd_nxt;

  bts = bt_get_sample (bt, bt->last_ooo);
  if (bts && bts->max_seq == start)
    {
      bts->max_seq = end;
      next = bt_next_sample (bt, bts);
      if (next)
        bt_fix_overlapped (bt, next, end, is_end);

      return;
    }

  /* Find original tx sample */
  bts = bt_lookup_seq (bt, start);

  ASSERT (bts != 0 && seq_geq (start, bts->min_seq));

  /* Head in the past */
  if (seq_lt (bts->min_seq, tc->snd_una))
    bt_update_sample (bt, bts, tc->snd_una);

  /* Head overlap */
  if (bts->min_seq == start)
    {
      prev_index = bts->prev;
      next = bt_fix_overlapped (bt, bts, end, is_end);
      next_index = bt_sample_index (bt, next);

      cur = tcp_bt_alloc_tx_sample (tc, start);
      cur->max_seq = end;
      cur->flags |= TCP_BTS_IS_RXT;
      cur->next = next_index;
      cur->prev = prev_index;

      cur_index = bt_sample_index (bt, cur);

      if (next_index != TCP_BTS_INVALID_INDEX)
        {
          next = bt_get_sample (bt, next_index);
          next->prev = cur_index;
        }
      else
        {
          bt->tail = cur_index;
        }

      if (prev_index != TCP_BTS_INVALID_INDEX)
        {
          prev = bt_get_sample (bt, prev_index);
          prev->next = cur_index;
        }
      else
        {
          bt->head = cur_index;
        }

      bt->last_ooo = cur_index;
      return;
    }

  bts_index = bt_sample_index (bt, bts);
  next = bt_next_sample (bt, bts);
  if (next)
    next = bt_fix_overlapped (bt, next, end, is_end);

  min_seq = next ? next->min_seq : tc->snd_nxt;
  ASSERT (seq_lt (start, min_seq));

  /* Have to split or tail overlap */
  cur = tcp_bt_alloc_tx_sample (tc, start);
  cur->max_seq = end;
  cur->flags |= TCP_BTS_IS_RXT;
  cur->prev = bts_index;
  cur_index = bt_sample_index (bt, cur);

  /* Split. Allocate another sample */
  if (seq_lt (end, min_seq))
    {
      nbts = tcp_bt_alloc_tx_sample (tc, end);
      cur = bt_get_sample (bt, cur_index);
      bts = bt_get_sample (bt, bts_index);

      *nbts = *bts;
      nbts->min_seq = end;

      if (nbts->next != TCP_BTS_INVALID_INDEX)
        {
          next = bt_get_sample (bt, nbts->next);
          next->prev = bt_sample_index (bt, nbts);
        }
      else
        bt->tail = bt_sample_index (bt, nbts);

      bts->next = nbts->prev = cur_index;
      cur->next = bt_sample_index (bt, nbts);

      bt->last_ooo = cur_index;
    }
  /* Tail completely overlapped */
  else
    {
      bts = bt_get_sample (bt, bts_index);

      if (bts->next != TCP_BTS_INVALID_INDEX)
        {
          next = bt_get_sample (bt, bts->next);
          next->prev = cur_index;
        }
      else
        bt->tail = cur_index;

      cur->next = bts->next;
      bts->next = cur_index;

      bt->last_ooo = cur_index;
    }
}

static void
tcp_bt_sample_to_rate_sample (tcp_connection_t * tc, tcp_bt_sample_t * bts,
                              tcp_rate_sample_t * rs)
{
  if (rs->prior_delivered && rs->prior_delivered >= bts->delivered)
    return;

  rs->prior_delivered = bts->delivered;
  rs->prior_time = bts->delivered_time;
  rs->rtt_time = bts->tx_time;
  rs->tx_rate = bts->tx_rate;
  rs->flags = bts->flags;
}

static void
tcp_bt_walk_samples (tcp_connection_t * tc, tcp_rate_sample_t * rs)
{
  tcp_byte_tracker_t *bt = tc->bt;
  tcp_bt_sample_t *next, *cur;

  cur = bt_get_sample (bt, bt->head);
  tcp_bt_sample_to_rate_sample (tc, cur, rs);
  while ((next = bt_get_sample (bt, cur->next))
         && seq_lt (next->min_seq, tc->snd_una))
    {
      bt_free_sample (bt, cur);
      tcp_bt_sample_to_rate_sample (tc, next, rs);
      cur = next;
    }

  ASSERT (seq_lt (cur->min_seq, tc->snd_una));

  /* All samples acked */
  if (tc->snd_una == tc->snd_nxt)
    {
      ASSERT (pool_elts (bt->samples) == 1);
      bt_free_sample (bt, cur);
      return;
    }

  /* Current sample completely consumed */
  if (next && next->min_seq == tc->snd_una)
    {
      bt_free_sample (bt, cur);
      cur = next;
    }
}

static void
tcp_bt_walk_samples_ooo (tcp_connection_t * tc, tcp_rate_sample_t * rs)
{
  sack_block_t *blks = tc->rcv_opts.sacks, *blk;
  tcp_byte_tracker_t *bt = tc->bt;
  tcp_bt_sample_t *next, *cur;
  int i;

  for (i = 0; i < vec_len (blks); i++)
    {
      blk = &blks[i];

      /* Ignore blocks that are already covered by snd_una */
      if (seq_lt (blk->end, tc->snd_una))
        continue;

      cur = bt_lookup_seq (bt, blk->start);
      if (!cur)
        continue;

      tcp_bt_sample_to_rate_sample (tc, cur, rs);

      /* Current shouldn't be removed */
      if (cur->min_seq != blk->start)
        {
          cur = bt_next_sample (bt, cur);
          if (!cur)
            continue;
        }

      while ((next = bt_get_sample (bt, cur->next))
             && seq_lt (next->min_seq, blk->end))
        {
          bt_free_sample (bt, cur);
          tcp_bt_sample_to_rate_sample (tc, next, rs);
          cur = next;
        }

      /* Current consumed entirely */
      if (next && next->min_seq == blk->end)
        bt_free_sample (bt, cur);
    }
}

void
tcp_bt_sample_delivery_rate (tcp_connection_t * tc, tcp_rate_sample_t * rs)
{
  u32 delivered;

  if (PREDICT_FALSE (tc->flags & TCP_CONN_FINSNT))
    return;

  delivered = tc->bytes_acked + tc->sack_sb.last_sacked_bytes;
  if (!delivered || tc->bt->head == TCP_BTS_INVALID_INDEX)
    return;

  /* Do not count bytes that were previously sacked again */
  tc->delivered += delivered - tc->sack_sb.last_bytes_delivered;
  tc->delivered_time = tcp_time_now_us (tc->c_thread_index);

  if (tc->app_limited && tc->delivered > tc->app_limited)
    tc->app_limited = 0;

  if (tc->bytes_acked)
    tcp_bt_walk_samples (tc, rs);

  if (tc->sack_sb.last_sacked_bytes)
    tcp_bt_walk_samples_ooo (tc, rs);

  rs->interval_time = tc->delivered_time - rs->prior_time;
  rs->delivered = tc->delivered - rs->prior_delivered;
  rs->rtt_time = tc->delivered_time - rs->rtt_time;
  rs->acked_and_sacked = delivered;
  rs->lost = tc->sack_sb.last_lost_bytes;
}

void
tcp_bt_flush_samples (tcp_connection_t * tc)
{
  tcp_byte_tracker_t *bt = tc->bt;
  tcp_bt_sample_t *bts;
  u32 *samples = 0, *si;

  vec_validate (samples, pool_elts (bt->samples) - 1);

  /* *INDENT-OFF* */
  pool_foreach (bts, bt->samples, ({
    vec_add1 (samples, bts - bt->samples);
  }));
  /* *INDENT-ON* */

  vec_foreach (si, samples)
  {
    bts = bt_get_sample (bt, *si);
    bt_free_sample (bt, bts);
  }

  vec_free (samples);
}

void
tcp_bt_cleanup (tcp_connection_t * tc)
{
  tcp_byte_tracker_t *bt = tc->bt;

  rb_tree_free_nodes (&bt->sample_lookup);
  pool_free (bt->samples);
  clib_mem_free (bt);
  tc->bt = 0;
}

void
tcp_bt_init (tcp_connection_t * tc)
{
  tcp_byte_tracker_t *bt;

  bt = clib_mem_alloc (sizeof (tcp_byte_tracker_t));
  clib_memset (bt, 0, sizeof (tcp_byte_tracker_t));

  rb_tree_init (&bt->sample_lookup);
  bt->head = bt->tail = TCP_BTS_INVALID_INDEX;
  tc->bt = bt;
}

/*
 * fd.io coding-style-patch-verification: ON
 *
 * Local Variables:
 * eval: (c-set-style "gnu")
 * End:
 */