svm_fifo.c

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/*
 * Copyright (c) 2016 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.
 */

#include "svm_fifo.h"

/** create an svm fifo, in the current heap. Fails vs blow up the process */
svm_fifo_t *
svm_fifo_create (u32 data_size_in_bytes)
{
  svm_fifo_t *f;
  pthread_mutexattr_t attr;
  pthread_condattr_t cattr;

  f = clib_mem_alloc_aligned_or_null (sizeof (*f) + data_size_in_bytes,
                                      CLIB_CACHE_LINE_BYTES);
  if (f == 0)
    return 0;

  memset (f, 0, sizeof (*f) + data_size_in_bytes);
  f->nitems = data_size_in_bytes;
  f->ooos_list_head = OOO_SEGMENT_INVALID_INDEX;

  memset (&attr, 0, sizeof (attr));
  memset (&cattr, 0, sizeof (cattr));

  if (pthread_mutexattr_init (&attr))
    clib_unix_warning ("mutexattr_init");
  if (pthread_mutexattr_setpshared (&attr, PTHREAD_PROCESS_SHARED))
    clib_unix_warning ("pthread_mutexattr_setpshared");
  if (pthread_mutex_init (&f->mutex, &attr))
    clib_unix_warning ("mutex_init");
  if (pthread_mutexattr_destroy (&attr))
    clib_unix_warning ("mutexattr_destroy");
  if (pthread_condattr_init (&cattr))
    clib_unix_warning ("condattr_init");
  if (pthread_condattr_setpshared (&cattr, PTHREAD_PROCESS_SHARED))
    clib_unix_warning ("condattr_setpshared");
  if (pthread_cond_init (&f->condvar, &cattr))
    clib_unix_warning ("cond_init1");
  if (pthread_condattr_destroy (&cattr))
    clib_unix_warning ("cond_init2");

  return (f);
}

always_inline ooo_segment_t *
ooo_segment_new (svm_fifo_t * f, u32 start, u32 length)
{
  ooo_segment_t *s;

  pool_get (f->ooo_segments, s);

  s->fifo_position = start;
  s->length = length;

  s->prev = s->next = OOO_SEGMENT_INVALID_INDEX;

  return s;
}

always_inline void
ooo_segment_del (svm_fifo_t * f, u32 index)
{
  ooo_segment_t *cur, *prev = 0, *next = 0;
  cur = pool_elt_at_index (f->ooo_segments, index);

  if (cur->next != OOO_SEGMENT_INVALID_INDEX)
    {
      next = pool_elt_at_index (f->ooo_segments, cur->next);
      next->prev = cur->prev;
    }

  if (cur->prev != OOO_SEGMENT_INVALID_INDEX)
    {
      prev = pool_elt_at_index (f->ooo_segments, cur->prev);
      prev->next = cur->next;
    }
  else
    {
      f->ooos_list_head = cur->next;
    }

  pool_put (f->ooo_segments, cur);
}

/**
 * Add segment to fifo's out-of-order segment list. Takes care of merging
 * adjacent segments and removing overlapping ones.
 */
static void
ooo_segment_add (svm_fifo_t * f, u32 offset, u32 length)
{
  ooo_segment_t *s, *new_s, *prev, *next, *it;
  u32 new_index, position, end_offset, s_sof, s_eof, s_index;

  position = (f->tail + offset) % f->nitems;
  end_offset = offset + length;

  if (f->ooos_list_head == OOO_SEGMENT_INVALID_INDEX)
    {
      s = ooo_segment_new (f, position, length);
      f->ooos_list_head = s - f->ooo_segments;
      f->ooos_newest = f->ooos_list_head;
      return;
    }

  /* Find first segment that starts after new segment */
  s = pool_elt_at_index (f->ooo_segments, f->ooos_list_head);
  while (s->next != OOO_SEGMENT_INVALID_INDEX
         && ooo_segment_offset (f, s) <= offset)
    s = pool_elt_at_index (f->ooo_segments, s->next);

  s_index = s - f->ooo_segments;
  s_sof = ooo_segment_offset (f, s);
  s_eof = ooo_segment_end_offset (f, s);

  /* No overlap, add before current segment */
  if (end_offset < s_sof)
    {
      new_s = ooo_segment_new (f, position, length);
      new_index = new_s - f->ooo_segments;

      /* Pool might've moved, get segment again */
      s = pool_elt_at_index (f->ooo_segments, s_index);

      if (s->prev != OOO_SEGMENT_INVALID_INDEX)
        {
          new_s->prev = s->prev;

          prev = pool_elt_at_index (f->ooo_segments, new_s->prev);
          prev->next = new_index;
        }
      else
        {
          /* New head */
          f->ooos_list_head = new_index;
        }

      new_s->next = s - f->ooo_segments;
      s->prev = new_index;
      f->ooos_newest = new_index;
      return;
    }
  /* No overlap, add after current segment */
  else if (s_eof < offset)
    {
      new_s = ooo_segment_new (f, position, length);
      new_index = new_s - f->ooo_segments;

      /* Pool might've moved, get segment again */
      s = pool_elt_at_index (f->ooo_segments, s_index);

      if (s->next != OOO_SEGMENT_INVALID_INDEX)
        {
          new_s->next = s->next;

          next = pool_elt_at_index (f->ooo_segments, new_s->next);
          next->prev = new_index;
        }

      new_s->prev = s - f->ooo_segments;
      s->next = new_index;
      f->ooos_newest = new_index;

      return;
    }

  /*
   * Merge needed
   */

  /* Merge at head */
  if (offset <= s_sof)
    {
      /* If we have a previous, check if we overlap */
      if (s->prev != OOO_SEGMENT_INVALID_INDEX)
        {
          prev = pool_elt_at_index (f->ooo_segments, s->prev);

          /* New segment merges prev and current. Remove previous and
           * update position of current. */
          if (ooo_segment_end_offset (f, prev) >= offset)
            {
              s->fifo_position = prev->fifo_position;
              s->length = s_eof - ooo_segment_offset (f, prev);
              ooo_segment_del (f, s->prev);
            }
        }
      else
        {
          s->fifo_position = position;
          s->length = s_eof - ooo_segment_offset (f, s);
        }

      /* The new segment's tail may cover multiple smaller ones */
      if (s_eof < end_offset)
        {
          /* Remove segments completely covered */
          it = (s->next != OOO_SEGMENT_INVALID_INDEX) ?
            pool_elt_at_index (f->ooo_segments, s->next) : 0;
          while (it && ooo_segment_end_offset (f, it) < end_offset)
            {
              next = (it->next != OOO_SEGMENT_INVALID_INDEX) ?
                pool_elt_at_index (f->ooo_segments, it->next) : 0;
              ooo_segment_del (f, it - f->ooo_segments);
              it = next;
            }

          /* Update length. Segment's start might have changed. */
          s->length = end_offset - ooo_segment_offset (f, s);

          /* If partial overlap with last, merge */
          if (it && ooo_segment_offset (f, it) < end_offset)
            {
              s->length +=
                it->length - (ooo_segment_offset (f, it) - end_offset);
              ooo_segment_del (f, it - f->ooo_segments);
            }
        }
    }
  /* Last but overlapping previous */
  else if (s_eof <= end_offset)
    {
      s->length = end_offset - ooo_segment_offset (f, s);
    }
  /* New segment completely covered by current one */
  else
    {
      /* Do Nothing */
    }

  /* Most recently updated segment */
  f->ooos_newest = s - f->ooo_segments;
}

/**
 * Removes segments that can now be enqueued because the fifo's tail has
 * advanced. Returns the number of bytes added to tail.
 */
static int
ooo_segment_try_collect (svm_fifo_t * f, u32 n_bytes_enqueued)
{
  ooo_segment_t *s;
  u32 index, bytes = 0, diff;

  s = pool_elt_at_index (f->ooo_segments, f->ooos_list_head);

  /* If last tail update overlaps one/multiple ooo segments, remove them */
  diff = (f->nitems + f->tail - s->fifo_position) % f->nitems;
  while (0 < diff && diff < n_bytes_enqueued)
    {
      /* Segment end is beyond the tail. Advance tail and be done */
      if (diff < s->length)
        {
          f->tail += s->length - diff;
          f->tail %= f->nitems;
          break;
        }
      /* If we have next go on */
      else if (s->next != OOO_SEGMENT_INVALID_INDEX)
        {
          index = s - f->ooo_segments;
          s = pool_elt_at_index (f->ooo_segments, s->next);
          diff = (f->nitems + f->tail - s->fifo_position) % f->nitems;
          ooo_segment_del (f, index);
        }
      /* End of search */
      else
        {
          break;
        }
    }

  /* If tail is adjacent to an ooo segment, 'consume' it */
  if (diff == 0)
    {
      bytes = ((f->nitems - f->cursize) >= s->length) ? s->length :
        f->nitems - f->cursize;

      f->tail += bytes;
      f->tail %= f->nitems;

      ooo_segment_del (f, s - f->ooo_segments);
    }

  return bytes;
}

static int
svm_fifo_enqueue_internal (svm_fifo_t * f,
                           int pid, u32 max_bytes, u8 * copy_from_here)
{
  u32 total_copy_bytes, first_copy_bytes, second_copy_bytes;
  u32 cursize, nitems;

  if (PREDICT_FALSE (f->cursize == f->nitems))
    return -2;                  /* fifo stuffed */

  /* read cursize, which can only decrease while we're working */
  cursize = f->cursize;
  nitems = f->nitems;

  /* Number of bytes we're going to copy */
  total_copy_bytes = (nitems - cursize) < max_bytes ?
    (nitems - cursize) : max_bytes;

  if (PREDICT_TRUE (copy_from_here != 0))
    {
      /* Number of bytes in first copy segment */
      first_copy_bytes = ((nitems - f->tail) < total_copy_bytes)
        ? (nitems - f->tail) : total_copy_bytes;

      clib_memcpy (&f->data[f->tail], copy_from_here, first_copy_bytes);
      f->tail += first_copy_bytes;
      f->tail = (f->tail == nitems) ? 0 : f->tail;

      /* Number of bytes in second copy segment, if any */
      second_copy_bytes = total_copy_bytes - first_copy_bytes;
      if (second_copy_bytes)
        {
          clib_memcpy (&f->data[f->tail], copy_from_here + first_copy_bytes,
                       second_copy_bytes);
          f->tail += second_copy_bytes;
          f->tail = (f->tail == nitems) ? 0 : f->tail;
        }
    }
  else
    {
      /* Account for a zero-copy enqueue done elsewhere */
      ASSERT (max_bytes <= (nitems - cursize));
      f->tail += max_bytes;
      f->tail = f->tail % nitems;
      total_copy_bytes = max_bytes;
    }

  /* Any out-of-order segments to collect? */
  if (PREDICT_FALSE (f->ooos_list_head != OOO_SEGMENT_INVALID_INDEX))
    total_copy_bytes += ooo_segment_try_collect (f, total_copy_bytes);

  /* Atomically increase the queue length */
  __sync_fetch_and_add (&f->cursize, total_copy_bytes);

  return (total_copy_bytes);
}

int
svm_fifo_enqueue_nowait (svm_fifo_t * f,
                         int pid, u32 max_bytes, u8 * copy_from_here)
{
  return svm_fifo_enqueue_internal (f, pid, max_bytes, copy_from_here);
}

/** Enqueue a future segment.
 * Two choices: either copies the entire segment, or copies nothing
 * Returns 0 of the entire segment was copied
 * Returns -1 if none of the segment was copied due to lack of space
 */

static int
svm_fifo_enqueue_with_offset_internal2 (svm_fifo_t * f,
                                        int pid,
                                        u32 offset,
                                        u32 required_bytes,
                                        u8 * copy_from_here)
{
  u32 total_copy_bytes, first_copy_bytes, second_copy_bytes;
  u32 cursize, nitems;
  u32 tail_plus_offset;

  ASSERT (offset > 0);

  /* read cursize, which can only decrease while we're working */
  cursize = f->cursize;
  nitems = f->nitems;

  /* Will this request fit? */
  if ((required_bytes + offset) > (nitems - cursize))
    return -1;

  ooo_segment_add (f, offset, required_bytes);

  /* Number of bytes we're going to copy */
  total_copy_bytes = required_bytes;
  tail_plus_offset = (f->tail + offset) % nitems;

  /* Number of bytes in first copy segment */
  first_copy_bytes = ((nitems - tail_plus_offset) < total_copy_bytes)
    ? (nitems - tail_plus_offset) : total_copy_bytes;

  clib_memcpy (&f->data[tail_plus_offset], copy_from_here, first_copy_bytes);

  /* Number of bytes in second copy segment, if any */
  second_copy_bytes = total_copy_bytes - first_copy_bytes;
  if (second_copy_bytes)
    {
      tail_plus_offset += first_copy_bytes;
      tail_plus_offset %= nitems;

      ASSERT (tail_plus_offset == 0);

      clib_memcpy (&f->data[tail_plus_offset],
                   copy_from_here + first_copy_bytes, second_copy_bytes);
    }

  return (0);
}


int
svm_fifo_enqueue_with_offset (svm_fifo_t * f,
                              int pid,
                              u32 offset,
                              u32 required_bytes, u8 * copy_from_here)
{
  return svm_fifo_enqueue_with_offset_internal2
    (f, pid, offset, required_bytes, copy_from_here);
}


static int
svm_fifo_dequeue_internal2 (svm_fifo_t * f,
                            int pid, u32 max_bytes, u8 * copy_here)
{
  u32 total_copy_bytes, first_copy_bytes, second_copy_bytes;
  u32 cursize, nitems;

  if (PREDICT_FALSE (f->cursize == 0))
    return -2;                  /* nothing in the fifo */

  /* read cursize, which can only increase while we're working */
  cursize = f->cursize;
  nitems = f->nitems;

  /* Number of bytes we're going to copy */
  total_copy_bytes = (cursize < max_bytes) ? cursize : max_bytes;

  if (PREDICT_TRUE (copy_here != 0))
    {
      /* Number of bytes in first copy segment */
      first_copy_bytes = ((nitems - f->head) < total_copy_bytes)
        ? (nitems - f->head) : total_copy_bytes;
      clib_memcpy (copy_here, &f->data[f->head], first_copy_bytes);
      f->head += first_copy_bytes;
      f->head = (f->head == nitems) ? 0 : f->head;

      /* Number of bytes in second copy segment, if any */
      second_copy_bytes = total_copy_bytes - first_copy_bytes;
      if (second_copy_bytes)
        {
          clib_memcpy (copy_here + first_copy_bytes,
                       &f->data[f->head], second_copy_bytes);
          f->head += second_copy_bytes;
          f->head = (f->head == nitems) ? 0 : f->head;
        }
    }
  else
    {
      /* Account for a zero-copy dequeue done elsewhere */
      ASSERT (max_bytes <= cursize);
      f->head += max_bytes;
      f->head = f->head % nitems;
      cursize -= max_bytes;
      total_copy_bytes = max_bytes;
    }

  __sync_fetch_and_sub (&f->cursize, total_copy_bytes);

  return (total_copy_bytes);
}

int
svm_fifo_dequeue_nowait (svm_fifo_t * f,
                         int pid, u32 max_bytes, u8 * copy_here)
{
  return svm_fifo_dequeue_internal2 (f, pid, max_bytes, copy_here);
}

int
svm_fifo_peek (svm_fifo_t * f, int pid, u32 offset, u32 max_bytes,
               u8 * copy_here)
{
  u32 total_copy_bytes, first_copy_bytes, second_copy_bytes;
  u32 cursize, nitems;

  if (PREDICT_FALSE (f->cursize == 0))
    return -2;                  /* nothing in the fifo */

  /* read cursize, which can only increase while we're working */
  cursize = f->cursize;
  nitems = f->nitems;

  /* Number of bytes we're going to copy */
  total_copy_bytes = (cursize < max_bytes) ? cursize : max_bytes;

  if (PREDICT_TRUE (copy_here != 0))
    {
      /* Number of bytes in first copy segment */
      first_copy_bytes =
        ((nitems - f->head + offset) < total_copy_bytes) ?
        (nitems - f->head + offset) : total_copy_bytes;
      clib_memcpy (copy_here, &f->data[f->head + offset], first_copy_bytes);

      /* Number of bytes in second copy segment, if any */
      second_copy_bytes = total_copy_bytes - first_copy_bytes;
      if (second_copy_bytes)
        {
          clib_memcpy (copy_here + first_copy_bytes, &f->data[0],
                       second_copy_bytes);
        }
    }
  return total_copy_bytes;
}

int
svm_fifo_dequeue_drop (svm_fifo_t * f, int pid, u32 max_bytes)
{
  u32 total_drop_bytes, first_drop_bytes, second_drop_bytes;
  u32 cursize, nitems;

  if (PREDICT_FALSE (f->cursize == 0))
    return -2;                  /* nothing in the fifo */

  /* read cursize, which can only increase while we're working */
  cursize = f->cursize;
  nitems = f->nitems;

  /* Number of bytes we're going to drop */
  total_drop_bytes = (cursize < max_bytes) ? cursize : max_bytes;

  /* Number of bytes in first copy segment */
  first_drop_bytes =
    ((nitems - f->head) < total_drop_bytes) ?
    (nitems - f->head) : total_drop_bytes;
  f->head += first_drop_bytes;
  f->head = (f->head == nitems) ? 0 : f->head;

  /* Number of bytes in second drop segment, if any */
  second_drop_bytes = total_drop_bytes - first_drop_bytes;
  if (second_drop_bytes)
    {
      f->head += second_drop_bytes;
      f->head = (f->head == nitems) ? 0 : f->head;
    }

  __sync_fetch_and_sub (&f->cursize, total_drop_bytes);

  return total_drop_bytes;
}

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