X-Git-Url: https://gerrit.fd.io/r/gitweb?a=blobdiff_plain;f=src%2Fsvm%2Fsvm_fifo.c;h=975a82026f7bb008051c4b51a389867ee7370c2f;hb=4d39f9c61c48d033ed5c9f729bdc975b58da29e8;hp=3512c72d9f16be60ddc57ca1b521d97cc8d65d93;hpb=87b15cebdaca21f6725637abeceec0f19f4eec51;p=vpp.git

diff --git a/src/svm/svm_fifo.c b/src/svm/svm_fifo.c
index 3512c72d9f1..975a82026f7 100644
--- a/src/svm/svm_fifo.c
+++ b/src/svm/svm_fifo.c
@@ -125,7 +125,7 @@ position_diff (svm_fifo_t * f, u32 a, u32 b, u32 tail)
 static inline u32
 ooo_segment_end_pos (svm_fifo_t * f, ooo_segment_t * s)
 {
-  return s->start + s->length;
+  return (s->start + s->length) % f->size;
 }
 
 void
@@ -135,7 +135,7 @@ svm_fifo_free_ooo_data (svm_fifo_t * f)
 }
 
 static inline ooo_segment_t *
-ooo_segment_get_prev (svm_fifo_t * f, ooo_segment_t * s)
+ooo_segment_prev (svm_fifo_t * f, ooo_segment_t * s)
 {
   if (s->prev == OOO_SEGMENT_INVALID_INDEX)
     return 0;
@@ -202,8 +202,8 @@ ooo_segment_add (svm_fifo_t * f, u32 offset, u32 head, u32 tail, u32 length)
 
   ASSERT (offset + length <= f_distance_to (f, head, tail) || head == tail);
 
-  offset_pos = tail + offset;
-  offset_end_pos = tail + offset + length;
+  offset_pos = (tail + offset) % f->size;
+  offset_end_pos = (tail + offset + length) % f->size;
 
   f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
 
@@ -222,7 +222,7 @@ ooo_segment_add (svm_fifo_t * f, u32 offset, u32 head, u32 tail, u32 length)
     s = pool_elt_at_index (f->ooo_segments, s->next);
 
   /* If we have a previous and we overlap it, use it as starting point */
-  prev = ooo_segment_get_prev (f, s);
+  prev = ooo_segment_prev (f, s);
   if (prev
       && position_leq (f, offset_pos, ooo_segment_end_pos (f, prev), tail))
     {
@@ -350,7 +350,7 @@ ooo_segment_try_collect (svm_fifo_t * f, u32 n_bytes_enqueued, u32 * tail)
       if (s->length > diff)
 	{
 	  bytes = s->length - diff;
-	  *tail = *tail + bytes;
+	  *tail = (*tail + bytes) % f->size;
 	  ooo_segment_free (f, s_index);
 	  break;
 	}
@@ -374,6 +374,20 @@ ooo_segment_try_collect (svm_fifo_t * f, u32 n_bytes_enqueued, u32 * tail)
   return bytes;
 }
 
+static ooo_segment_t *
+ooo_segment_last (svm_fifo_t * f)
+{
+  ooo_segment_t *s;
+
+  if (f->ooos_list_head == OOO_SEGMENT_INVALID_INDEX)
+    return 0;
+
+  s = svm_fifo_first_ooo_segment (f);
+  while (s->next != OOO_SEGMENT_INVALID_INDEX)
+    s = pool_elt_at_index (f->ooo_segments, s->next);
+  return s;
+}
+
 void
 svm_fifo_init (svm_fifo_t * f, u32 size)
 {
@@ -386,29 +400,66 @@ svm_fifo_init (svm_fifo_t * f, u32 size)
   f->ooos_list_head = OOO_SEGMENT_INVALID_INDEX;
   f->segment_index = SVM_FIFO_INVALID_INDEX;
   f->refcnt = 1;
-  f->default_chunk.start_byte = 0;
-  f->default_chunk.length = f->size;
-  f->default_chunk.next = f->start_chunk = f->end_chunk = &f->default_chunk;
+  f->head = f->tail = f->flags = 0;
   f->head_chunk = f->tail_chunk = f->ooo_enq = f->ooo_deq = f->start_chunk;
 }
 
+void
+svm_fifo_init_chunks (svm_fifo_t * f)
+{
+  svm_fifo_chunk_t *c, *prev;
+
+  if (f->start_chunk->next == f->start_chunk)
+    return;
+
+  f->flags |= SVM_FIFO_F_MULTI_CHUNK;
+  rb_tree_init (&f->chunk_lookup);
+  rb_tree_add2 (&f->chunk_lookup, 0, pointer_to_uword (f->start_chunk));
+
+  f->start_chunk->start_byte = 0;
+  prev = f->start_chunk;
+  c = prev->next;
+
+  while (c != f->start_chunk)
+    {
+      c->start_byte = prev->start_byte + prev->length;
+      rb_tree_add2 (&f->chunk_lookup, c->start_byte, pointer_to_uword (c));
+      prev = c;
+      c = c->next;
+    }
+}
+
 /**
  * Creates a 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;
   u32 rounded_data_size;
+  svm_fifo_chunk_t *c;
+  svm_fifo_t *f;
 
-  /* always round fifo data size to the next highest power-of-two */
-  rounded_data_size = (1 << (max_log2 (data_size_in_bytes)));
-  f = clib_mem_alloc_aligned_or_null (sizeof (*f) + rounded_data_size,
-				      CLIB_CACHE_LINE_BYTES);
+  f = clib_mem_alloc_aligned_or_null (sizeof (*f), CLIB_CACHE_LINE_BYTES);
   if (f == 0)
     return 0;
 
   clib_memset (f, 0, sizeof (*f));
+
+  /* always round fifo data size to the next highest power-of-two */
+  rounded_data_size = (1 << (max_log2 (data_size_in_bytes)));
+  c = clib_mem_alloc_aligned_or_null (sizeof (*c) + rounded_data_size,
+				      CLIB_CACHE_LINE_BYTES);
+  if (!c)
+    {
+      clib_mem_free (f);
+      return 0;
+    }
+
+  c->next = c;
+  c->start_byte = 0;
+  c->length = data_size_in_bytes;
+  f->start_chunk = f->end_chunk = c;
+
   svm_fifo_init (f, data_size_in_bytes);
   return f;
 }
@@ -434,8 +485,65 @@ svm_fifo_chunk_alloc (u32 size)
   return c;
 }
 
+static inline u8
+svm_fifo_chunk_includes_pos (svm_fifo_chunk_t * c, u32 pos)
+{
+  return (pos >= c->start_byte && pos < c->start_byte + c->length);
+}
+
+/**
+ * Find chunk for given byte position
+ *
+ * @param f	fifo
+ * @param pos	normalized position in fifo
+ *
+ * @return chunk that includes given position or 0
+ */
+static svm_fifo_chunk_t *
+svm_fifo_find_chunk (svm_fifo_t * f, u32 pos)
+{
+  rb_tree_t *rt = &f->chunk_lookup;
+  rb_node_t *cur, *prev;
+  svm_fifo_chunk_t *c;
+
+  cur = rb_node (rt, rt->root);
+  while (pos != cur->key)
+    {
+      prev = cur;
+      if (pos < 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 (pos < prev->key)
+	    {
+	      cur = rb_tree_predecessor (rt, prev);
+	      if (rb_node_is_tnil (rt, cur))
+		return 0;
+	      c = uword_to_pointer (cur->opaque, svm_fifo_chunk_t *);
+	      if (svm_fifo_chunk_includes_pos (c, pos))
+		return c;
+	      return 0;
+	    }
+	  /* Hit tnil as a right child. Check if this is the one */
+	  c = uword_to_pointer (prev->opaque, svm_fifo_chunk_t *);
+	  if (svm_fifo_chunk_includes_pos (c, pos))
+	    return c;
+
+	  return 0;
+	}
+    }
+
+  if (!rb_node_is_tnil (rt, cur))
+    return uword_to_pointer (cur->opaque, svm_fifo_chunk_t *);
+  return 0;
+}
+
 static inline void
-svm_fifo_size_update (svm_fifo_t * f, svm_fifo_chunk_t * c)
+svm_fifo_grow (svm_fifo_t * f, svm_fifo_chunk_t * c)
 {
   svm_fifo_chunk_t *prev;
   u32 add_bytes = 0;
@@ -458,13 +566,13 @@ svm_fifo_size_update (svm_fifo_t * f, svm_fifo_chunk_t * c)
 }
 
 static void
-svm_fifo_try_size_update (svm_fifo_t * f, u32 new_head)
+svm_fifo_try_grow (svm_fifo_t * f, u32 new_head)
 {
-  if (new_head % f->size > f->tail % f->size)
+  if (new_head > f->tail)
     return;
 
-  svm_fifo_size_update (f, f->new_chunks);
-  f->flags &= ~SVM_FIFO_F_SIZE_UPDATE;
+  svm_fifo_grow (f, f->new_chunks);
+  f->flags &= ~SVM_FIFO_F_GROW;
 }
 
 void
@@ -472,16 +580,106 @@ svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c)
 {
   svm_fifo_chunk_t *cur, *prev;
 
-  /* Initialize rbtree if needed and add default chunk to it */
+  /* Initialize rbtree if needed and add default chunk to it. Expectation is
+   * that this is called with the heap where the rbtree's pool is pushed. */
   if (!(f->flags & SVM_FIFO_F_MULTI_CHUNK))
     {
+      ASSERT (f->start_chunk->next == f->start_chunk);
       rb_tree_init (&f->chunk_lookup);
       rb_tree_add2 (&f->chunk_lookup, 0, pointer_to_uword (f->start_chunk));
       f->flags |= SVM_FIFO_F_MULTI_CHUNK;
     }
 
-  /* Initialize chunks and add to lookup rbtree. Expectation is that this is
-   * called with the heap where the rbtree's pool is pushed. */
+  /* If fifo is not wrapped, update the size now */
+  if (!svm_fifo_is_wrapped (f))
+    {
+      /* Initialize chunks and add to lookup rbtree */
+      cur = c;
+      if (f->new_chunks)
+	{
+	  prev = f->new_chunks;
+	  while (prev->next)
+	    prev = prev->next;
+	  prev->next = c;
+	}
+      else
+	prev = f->end_chunk;
+
+      while (cur)
+	{
+	  cur->start_byte = prev->start_byte + prev->length;
+	  rb_tree_add2 (&f->chunk_lookup, cur->start_byte,
+			pointer_to_uword (cur));
+	  prev = cur;
+	  cur = cur->next;
+	}
+
+      ASSERT (!f->new_chunks);
+      svm_fifo_grow (f, c);
+      return;
+    }
+
+  /* Wrapped */
+  if (f->flags & SVM_FIFO_F_SINGLE_THREAD_OWNED)
+    {
+      ASSERT (f->master_thread_index == os_get_thread_index ());
+
+      if (!f->new_chunks && f->head_chunk != f->tail_chunk)
+	{
+	  u32 head = 0, tail = 0;
+	  f_load_head_tail_cons (f, &head, &tail);
+
+	  svm_fifo_chunk_t *tmp = f->tail_chunk->next;
+
+	  prev = f->tail_chunk;
+	  u32 add_bytes = 0;
+	  cur = prev->next;
+	  while (cur != f->start_chunk)
+	    {
+	      /* remove any existing rb_tree entry */
+	      rb_tree_del (&f->chunk_lookup, cur->start_byte);
+	      cur = cur->next;
+	    }
+
+	  /* insert new chunk after the tail_chunk */
+	  f->tail_chunk->next = c;
+	  while (c)
+	    {
+	      add_bytes += c->length;
+	      c->start_byte = prev->start_byte + prev->length;
+	      rb_tree_add2 (&f->chunk_lookup, c->start_byte,
+			    pointer_to_uword (c));
+
+	      prev = c;
+	      c = c->next;
+	    }
+	  prev->next = tmp;
+
+	  /* shift existing chunks along */
+	  cur = tmp;
+	  while (cur != f->start_chunk)
+	    {
+	      cur->start_byte = prev->start_byte + prev->length;
+	      rb_tree_add2 (&f->chunk_lookup, cur->start_byte,
+			    pointer_to_uword (cur));
+	      prev = cur;
+	      cur = cur->next;
+	    }
+
+	  f->size += add_bytes;
+	  f->nitems = f->size - 1;
+	  f->new_chunks = 0;
+	  head += add_bytes;
+
+	  clib_atomic_store_rel_n (&f->head, head);
+	  ASSERT (svm_fifo_is_sane (f));
+
+	  return;
+	}
+    }
+
+  /* Wrapped, and optimization of single-thread-owned fifo cannot be applied */
+  /* Initialize chunks and add to lookup rbtree */
   cur = c;
   if (f->new_chunks)
     {
@@ -502,75 +700,147 @@ svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c)
       cur = cur->next;
     }
 
-  /* If fifo is not wrapped, update the size now */
-  if (!svm_fifo_is_wrapped (f))
-    {
-      ASSERT (!f->new_chunks);
-      svm_fifo_size_update (f, c);
-      return;
-    }
-
   /* Postpone size update */
   if (!f->new_chunks)
     {
       f->new_chunks = c;
-      f->flags |= SVM_FIFO_F_SIZE_UPDATE;
+      f->flags |= SVM_FIFO_F_GROW;
     }
 }
 
-static inline u8
-svm_fifo_chunk_includes_pos (svm_fifo_chunk_t * c, u32 pos)
+/**
+ * Removes chunks that are after fifo end byte
+ */
+svm_fifo_chunk_t *
+svm_fifo_collect_chunks (svm_fifo_t * f)
 {
-  return (pos >= c->start_byte && pos < c->start_byte + c->length);
+  svm_fifo_chunk_t *list, *cur;
+
+  f->flags &= ~SVM_FIFO_F_COLLECT_CHUNKS;
+
+  list = f->new_chunks;
+  f->new_chunks = 0;
+  cur = list;
+  while (cur)
+    {
+      rb_tree_del (&f->chunk_lookup, cur->start_byte);
+      cur = cur->next;
+    }
+
+  return list;
+}
+
+void
+svm_fifo_try_shrink (svm_fifo_t * f, u32 head, u32 tail)
+{
+  u32 len_to_shrink = 0, tail_pos, len, last_pos;
+  svm_fifo_chunk_t *cur, *prev, *next, *start;
+
+  tail_pos = tail;
+  if (f->ooos_list_head != OOO_SEGMENT_INVALID_INDEX)
+    {
+      ooo_segment_t *last = ooo_segment_last (f);
+      tail_pos = ooo_segment_end_pos (f, last);
+    }
+
+  if (f->size_decrement)
+    {
+      /* Figure out available free space considering that there may be
+       * ooo segments */
+      len = clib_min (f->size_decrement, f_free_count (f, head, tail_pos));
+      f->nitems -= len;
+      f->size_decrement -= len;
+    }
+
+  /* Remove tail chunks if the following hold:
+   * - not wrapped
+   * - last used byte less than start of last chunk
+   */
+  if (tail_pos >= head && tail_pos < f->end_chunk->start_byte)
+    {
+      /* Lookup the last position not to be removed. Since size still needs
+       * to be nitems + 1, nitems must fall within the usable space. Also,
+       * first segment is not removable, so tail_pos can be 0. */
+      last_pos = tail_pos > 0 ? tail_pos - 1 : tail_pos;
+      prev = svm_fifo_find_chunk (f, clib_max (f->nitems, last_pos));
+      next = prev->next;
+      /* If tail_pos is first position in next, skip the chunk, otherwise,
+       * we must update the tail and, if fifo size is 0, even the head.
+       * We should not invalidate the tail for the caller and must not change
+       * consumer owned variables from code that's typically called by the
+       * producer */
+      if (next->start_byte == tail_pos)
+	{
+	  prev = next;
+	  next = next->next;
+	}
+      while (next != f->start_chunk)
+	{
+	  cur = next;
+	  next = cur->next;
+	  len_to_shrink += cur->length;
+	}
+      if (len_to_shrink)
+	{
+	  f->size -= len_to_shrink;
+	  start = prev->next;
+	  prev->next = f->start_chunk;
+	  f->end_chunk = prev;
+	  cur->next = f->new_chunks;
+	  f->new_chunks = start;
+	}
+    }
+
+  if (!f->size_decrement && f->size == f->nitems + 1)
+    {
+      f->flags &= ~SVM_FIFO_F_SHRINK;
+      f->flags |= SVM_FIFO_F_COLLECT_CHUNKS;
+      if (f->start_chunk == f->start_chunk->next)
+	f->flags &= ~SVM_FIFO_F_MULTI_CHUNK;
+    }
 }
 
 /**
- * Find chunk for given byte position
- *
- * @param f	fifo
- * @param pos	normalized position in fifo
- *
- * @return chunk that includes given position or 0
+ * Request to reduce fifo size by amount of bytes
  */
-static svm_fifo_chunk_t *
-svm_fifo_find_chunk (svm_fifo_t * f, u32 pos)
+int
+svm_fifo_reduce_size (svm_fifo_t * f, u32 len, u8 try_shrink)
 {
-  rb_tree_t *rt = &f->chunk_lookup;
-  rb_node_t *cur, *prev;
-  svm_fifo_chunk_t *c;
+  svm_fifo_chunk_t *cur;
+  u32 actual_len = 0;
 
-  cur = rb_node (rt, rt->root);
-  while (pos != cur->key)
+  /* Abort if trying to reduce by more than fifo size or if
+   * fifo is undergoing resizing already */
+  if (len >= f->size || f->size > f->nitems + 1
+      || (f->flags & SVM_FIFO_F_SHRINK) || (f->flags & SVM_FIFO_F_GROW))
+    return 0;
+
+  /* last chunk that will not be removed */
+  cur = svm_fifo_find_chunk (f, f->nitems - len);
+
+  /* sum length of chunks that will be removed */
+  cur = cur->next;
+  while (cur != f->start_chunk)
     {
-      prev = cur;
-      if (pos < cur->key)
-	cur = rb_node_left (rt, cur);
-      else
-	cur = rb_node_right (rt, cur);
+      actual_len += cur->length;
+      cur = cur->next;
+    }
 
-      if (rb_node_is_tnil (rt, cur))
-	{
-	  /* Hit tnil as a left child. Find predecessor */
-	  if (pos < prev->key)
-	    {
-	      cur = rb_tree_predecessor (rt, prev);
-	      c = uword_to_pointer (cur->opaque, svm_fifo_chunk_t *);
-	      if (svm_fifo_chunk_includes_pos (c, pos))
-		return c;
-	      return 0;
-	    }
-	  /* Hit tnil as a right child. Check if this is the one */
-	  c = uword_to_pointer (prev->opaque, svm_fifo_chunk_t *);
-	  if (svm_fifo_chunk_includes_pos (c, pos))
-	    return c;
+  ASSERT (actual_len <= len);
+  if (!actual_len)
+    return 0;
 
-	  return 0;
-	}
+  f->size_decrement = actual_len;
+  f->flags |= SVM_FIFO_F_SHRINK;
+
+  if (try_shrink)
+    {
+      u32 head, tail;
+      f_load_head_tail_prod (f, &head, &tail);
+      svm_fifo_try_shrink (f, head, tail);
     }
 
-  if (!rb_node_is_tnil (rt, cur))
-    return uword_to_pointer (cur->opaque, svm_fifo_chunk_t *);
-  return 0;
+  return actual_len;
 }
 
 void
@@ -603,8 +873,7 @@ svm_fifo_overwrite_head (svm_fifo_t * f, u8 * src, u32 len)
 
   f_load_head_tail_cons (f, &head, &tail);
   c = f->head_chunk;
-  head_idx = head % f->size;
-  head_idx -= c->start_byte;
+  head_idx = head - c->start_byte;
   n_chunk = c->length - head_idx;
   if (len <= n_chunk)
     clib_memcpy_fast (&c->data[head_idx], src, len);
@@ -632,15 +901,18 @@ svm_fifo_enqueue (svm_fifo_t * f, u32 len, const u8 * src)
 
   /* number of bytes we're going to copy */
   len = clib_min (free_count, len);
-  svm_fifo_copy_to_chunk (f, f->tail_chunk, tail % f->size, src, len,
-			  &f->tail_chunk);
-  tail += len;
+  svm_fifo_copy_to_chunk (f, f->tail_chunk, tail, src, len, &f->tail_chunk);
+  tail = (tail + len) % f->size;
 
   svm_fifo_trace_add (f, head, len, 2);
 
   /* collect out-of-order segments */
   if (PREDICT_FALSE (f->ooos_list_head != OOO_SEGMENT_INVALID_INDEX))
-    len += ooo_segment_try_collect (f, len, &tail);
+    {
+      len += ooo_segment_try_collect (f, len, &tail);
+      if (!svm_fifo_chunk_includes_pos (f->tail_chunk, tail))
+	f->tail_chunk = svm_fifo_find_chunk (f, tail);
+    }
 
   /* store-rel: producer owned index (paired with load-acq in consumer) */
   clib_atomic_store_rel_n (&f->tail, tail);
@@ -662,6 +934,9 @@ svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len, u8 * src)
 
   f_load_head_tail_prod (f, &head, &tail);
 
+  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_SHRINK))
+    svm_fifo_try_shrink (f, head, tail);
+
   /* free space in fifo can only increase during enqueue: SPSC */
   free_count = f_free_count (f, head, tail);
 
@@ -672,7 +947,7 @@ svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len, u8 * src)
   f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
   svm_fifo_trace_add (f, offset, len, 1);
   ooo_segment_add (f, offset, head, tail, len);
-  tail_idx = (tail % f->size + offset) % f->size;
+  tail_idx = (tail + offset) % f->size;
 
   if (!svm_fifo_chunk_includes_pos (f->ooo_enq, tail_idx))
     f->ooo_enq = svm_fifo_find_chunk (f, tail_idx);
@@ -682,6 +957,26 @@ svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len, u8 * src)
   return 0;
 }
 
+/**
+ * Advance tail
+ */
+void
+svm_fifo_enqueue_nocopy (svm_fifo_t * f, u32 len)
+{
+  u32 tail;
+
+  ASSERT (len <= svm_fifo_max_enqueue_prod (f));
+  /* load-relaxed: producer owned index */
+  tail = f->tail;
+  tail = (tail + len) % f->size;
+
+  if (!svm_fifo_chunk_includes_pos (f->tail_chunk, tail))
+    f->tail_chunk = svm_fifo_find_chunk (f, tail);
+
+  /* store-rel: producer owned index (paired with load-acq in consumer) */
+  clib_atomic_store_rel_n (&f->tail, tail);
+}
+
 int
 svm_fifo_dequeue (svm_fifo_t * f, u32 len, u8 * dst)
 {
@@ -696,12 +991,11 @@ svm_fifo_dequeue (svm_fifo_t * f, u32 len, u8 * dst)
     return SVM_FIFO_EEMPTY;
 
   len = clib_min (cursize, len);
-  svm_fifo_copy_from_chunk (f, f->head_chunk, head % f->size, dst, len,
-			    &f->head_chunk);
-  head += len;
+  svm_fifo_copy_from_chunk (f, f->head_chunk, head, dst, len, &f->head_chunk);
+  head = (head + len) % f->size;
 
-  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_SIZE_UPDATE))
-    svm_fifo_try_size_update (f, head);
+  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_GROW))
+    svm_fifo_try_grow (f, head);
 
   /* store-rel: consumer owned index (paired with load-acq in producer) */
   clib_atomic_store_rel_n (&f->head, head);
@@ -723,7 +1017,7 @@ svm_fifo_peek (svm_fifo_t * f, u32 offset, u32 len, u8 * dst)
     return SVM_FIFO_EEMPTY;
 
   len = clib_min (cursize - offset, len);
-  head_idx = (head % f->size + offset) % f->size;
+  head_idx = (head + offset) % f->size;
   if (!svm_fifo_chunk_includes_pos (f->ooo_deq, head_idx))
     f->ooo_deq = svm_fifo_find_chunk (f, head_idx);
 
@@ -743,13 +1037,19 @@ svm_fifo_dequeue_drop (svm_fifo_t * f, u32 len)
   if (PREDICT_FALSE (cursize == 0))
     return SVM_FIFO_EEMPTY;
 
-  svm_fifo_trace_add (f, tail, total_drop_bytes, 3);
-
   /* number of bytes we're going to drop */
   total_drop_bytes = clib_min (cursize, len);
 
+  svm_fifo_trace_add (f, tail, total_drop_bytes, 3);
+
   /* move head */
-  head += total_drop_bytes;
+  head = (head + total_drop_bytes) % f->size;
+
+  if (!svm_fifo_chunk_includes_pos (f->head_chunk, head))
+    f->head_chunk = svm_fifo_find_chunk (f, head);
+
+  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_GROW))
+    svm_fifo_try_grow (f, head);
 
   /* store-rel: consumer owned index (paired with load-acq in producer) */
   clib_atomic_store_rel_n (&f->head, head);
@@ -762,6 +1062,13 @@ svm_fifo_dequeue_drop_all (svm_fifo_t * f)
 {
   /* consumer foreign index */
   u32 tail = clib_atomic_load_acq_n (&f->tail);
+
+  if (!svm_fifo_chunk_includes_pos (f->head_chunk, tail))
+    f->head_chunk = svm_fifo_find_chunk (f, tail);
+
+  if (PREDICT_FALSE (f->flags & SVM_FIFO_F_GROW))
+    svm_fifo_try_grow (f, tail);
+
   /* store-rel: consumer owned index (paired with load-acq in producer) */
   clib_atomic_store_rel_n (&f->head, tail);
 }
@@ -779,7 +1086,7 @@ svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs)
   if (PREDICT_FALSE (cursize == 0))
     return SVM_FIFO_EEMPTY;
 
-  head_idx = head % f->size;
+  head_idx = head;
 
   if (tail < head)
     {
@@ -801,14 +1108,13 @@ svm_fifo_segments (svm_fifo_t * f, svm_fifo_seg_t * fs)
 void
 svm_fifo_segments_free (svm_fifo_t * f, svm_fifo_seg_t * fs)
 {
-  u32 head, head_idx;
+  u32 head;
 
   /* consumer owned index */
   head = f->head;
-  head_idx = head % f->size;
 
-  ASSERT (fs[0].data == f->head_chunk->data + head_idx);
-  head += fs[0].len + fs[1].len;
+  ASSERT (fs[0].data == f->head_chunk->data + head);
+  head = (head + fs[0].len + fs[1].len) % f->size;
   /* store-rel: consumer owned index (paired with load-acq in producer) */
   clib_atomic_store_rel_n (&f->head, head);
 }
@@ -849,15 +1155,17 @@ svm_fifo_first_ooo_segment (svm_fifo_t * f)
 void
 svm_fifo_init_pointers (svm_fifo_t * f, u32 head, u32 tail)
 {
+  head = head % f->size;
+  tail = tail % f->size;
   clib_atomic_store_rel_n (&f->head, head);
   clib_atomic_store_rel_n (&f->tail, tail);
   if (f->flags & SVM_FIFO_F_MULTI_CHUNK)
     {
       svm_fifo_chunk_t *c;
-      c = svm_fifo_find_chunk (f, head % f->size);
+      c = svm_fifo_find_chunk (f, head);
       ASSERT (c != 0);
       f->head_chunk = f->ooo_deq = c;
-      c = svm_fifo_find_chunk (f, tail % f->size);
+      c = svm_fifo_find_chunk (f, tail);
       ASSERT (c != 0);
       f->tail_chunk = f->ooo_enq = c;
     }
@@ -886,6 +1194,64 @@ svm_fifo_del_subscriber (svm_fifo_t * f, u8 subscriber)
     }
 }
 
+u8
+svm_fifo_is_sane (svm_fifo_t * f)
+{
+  if (f->size - 1 != f->nitems && !(f->flags & SVM_FIFO_F_SHRINK))
+    return 0;
+  if (!svm_fifo_chunk_includes_pos (f->head_chunk, f->head))
+    return 0;
+  if (!svm_fifo_chunk_includes_pos (f->tail_chunk, f->tail))
+    return 0;
+
+  if (f->start_chunk->next != f->start_chunk)
+    {
+      svm_fifo_chunk_t *c, *prev = 0, *tmp;
+      u32 size = 0;
+
+      if (!(f->flags & SVM_FIFO_F_MULTI_CHUNK))
+	return 0;
+
+      c = f->start_chunk;
+      do
+	{
+	  tmp = svm_fifo_find_chunk (f, c->start_byte);
+	  if (tmp != c)
+	    return 0;
+	  if (prev && (prev->start_byte + prev->length != c->start_byte))
+	    return 0;
+	  size += c->length;
+	  prev = c;
+	  c = c->next;
+	}
+      while (c != f->start_chunk);
+
+      if (size != f->size)
+	return 0;
+    }
+
+  return 1;
+}
+
+u8
+svm_fifo_set_single_thread_owned (svm_fifo_t * f)
+{
+  if (f->flags & SVM_FIFO_F_SINGLE_THREAD_OWNED)
+    {
+      if (f->master_thread_index == os_get_thread_index ())
+	{
+	  /* just a duplicate call */
+	  return 0;
+	}
+
+      /* already owned by another thread */
+      return 1;
+    }
+
+  f->flags |= SVM_FIFO_F_SINGLE_THREAD_OWNED;
+  return 0;
+}
+
 u8 *
 format_ooo_segment (u8 * s, va_list * args)
 {