svm: more fifo refactor/cleanup

Change-Id: Ie76c69641c8598164d0d00fd498018037258fd86
Signed-off-by: Florin Coras <fcoras@cisco.com>

1 files changed, 461 insertions, 217 deletions

diff --git a/src/svm/svm_fifo.h b/src/svm/svm_fifo.h
index c9370955dfb..96ca3ee01c6 100644
--- a/src/svm/svm_fifo.h
+++ b/src/svm/svm_fifo.h
@@ -30,7 +30,6 @@ typedef struct
 {
   u32 next;	/**< Next linked-list element pool index */
   u32 prev;	/**< Previous linked-list element pool index */
-
   u32 start;	/**< Start of segment, normalized*/
   u32 length;	/**< Length of segment */
 } ooo_segment_t;
@@ -41,12 +40,12 @@ typedef struct
 #define SVM_FIFO_INVALID_INDEX		((u32)~0)
 #define SVM_FIFO_MAX_EVT_SUBSCRIBERS	7
 
-enum svm_fifo_tx_ntf_
+typedef enum svm_fifo_tx_ntf_
 {
   SVM_FIFO_NO_TX_NOTIF = 0,
   SVM_FIFO_WANT_TX_NOTIF = 1,
   SVM_FIFO_WANT_TX_NOTIF_IF_FULL = 2,
-};
+} svm_fifo_tx_ntf_t;
 
 typedef struct
 {
@@ -57,10 +56,10 @@ typedef struct
 
 typedef struct svm_fifo_chunk_
 {
-  u32 start_byte;
-  u32 length;
-  struct svm_fifo_chunk_ *next;
-  u8 data[0];
+  u32 start_byte;		/**< chunk start byte */
+  u32 length;			/**< length of chunk in bytes */
+  struct svm_fifo_chunk_ *next;	/**< pointer to next chunk in linked-lists */
+  u8 data[0];			/**< start of chunk data */
 } svm_fifo_chunk_t;
 
 typedef enum svm_fifo_flag_
@@ -73,8 +72,8 @@ typedef enum svm_fifo_flag_
 typedef struct _svm_fifo
 {
   CLIB_CACHE_LINE_ALIGN_MARK (shared_first);
-  u32 size;			/**< size of the fifo */
-  u32 nitems;			/**< usable size(size-1) */
+  u32 size;			/**< size of the fifo in bytes */
+  u32 nitems;			/**< usable size (size-1) */
   u8 flags;			/**< fifo flags */
   svm_fifo_chunk_t *start_chunk;/**< first chunk in fifo chunk list */
   svm_fifo_chunk_t *end_chunk;	/**< end chunk in fifo chunk list */
@@ -83,14 +82,12 @@ typedef struct _svm_fifo
 
     CLIB_CACHE_LINE_ALIGN_MARK (shared_second);
   volatile u32 has_event;	/**< non-zero if deq event exists */
-
-  u32 master_session_index;
-  u32 client_session_index;
-  u8 master_thread_index;
-  u8 client_thread_index;
-  u32 segment_manager;
-  u32 segment_index;
-  u32 ct_session_index;		/**< Local session index for vpp */
+  u32 master_session_index;	/**< session layer session index */
+  u32 client_session_index;	/**< app session index */
+  u8 master_thread_index;	/**< session layer thread index */
+  u8 client_thread_index;	/**< app worker index */
+  u32 segment_manager;		/**< session layer segment manager index */
+  u32 segment_index;		/**< segment index in segment manager */
   u32 freelist_index;		/**< aka log2(allocated_size) - const. */
   i8 refcnt;			/**< reference count  */
   struct _svm_fifo *next;	/**< next in freelist/active chain */
@@ -110,7 +107,7 @@ typedef struct _svm_fifo
   svm_fifo_chunk_t *ooo_enq;	/**< last chunk used for ooo enqueue */
   ooo_segment_t *ooo_segments;	/**< Pool of ooo segments */
   u32 ooos_newest;		/**< Last segment to have been updated */
-  volatile u8 n_subscribers;
+  volatile u8 n_subscribers;	/**< Number of subscribers for io events */
   u8 subscribers[SVM_FIFO_MAX_EVT_SUBSCRIBERS];
 
 #if SVM_FIFO_TRACE
@@ -122,7 +119,8 @@ typedef struct _svm_fifo
 
 typedef enum
 {
-  SVM_FIFO_FULL = -2,
+  SVM_FIFO_EFULL = -2,
+  SVM_FIFO_EEMPTY = -3,
 } svm_fifo_err_t;
 
 typedef struct svm_fifo_seg_
@@ -147,7 +145,11 @@ typedef struct svm_fifo_seg_
 u8 *svm_fifo_dump_trace (u8 * s, svm_fifo_t * f);
 u8 *svm_fifo_replay (u8 * s, svm_fifo_t * f, u8 no_read, u8 verbose);
 
-/* internal function */
+/**
+ * Load head and tail optimized for consumer
+ *
+ * Internal function.
+ */
 static inline void
 f_load_head_tail_cons (svm_fifo_t * f, u32 * head, u32 * tail)
 {
@@ -157,7 +159,10 @@ f_load_head_tail_cons (svm_fifo_t * f, u32 * head, u32 * tail)
   *tail = clib_atomic_load_acq_n (&f->tail);
 }
 
-/* internal function */
+/** Load head and tail optimized for producer
+ *
+ * Internal function
+ */
 static inline void
 f_load_head_tail_prod (svm_fifo_t * f, u32 * head, u32 * tail)
 {
@@ -167,8 +172,10 @@ f_load_head_tail_prod (svm_fifo_t * f, u32 * head, u32 * tail)
   *head = clib_atomic_load_acq_n (&f->head);
 }
 
-/* producer consumer role independent */
-/* internal function */
+/* Load head and tail independent of producer/consumer role
+ *
+ * Internal function.
+ */
 static inline void
 f_load_head_tail_all_acq (svm_fifo_t * f, u32 * head, u32 * tail)
 {
@@ -178,21 +185,247 @@ f_load_head_tail_all_acq (svm_fifo_t * f, u32 * head, u32 * tail)
   *head = clib_atomic_load_acq_n (&f->head);
 }
 
-/* internal function */
+/**
+ * Fifo free bytes, i.e., number of free bytes
+ *
+ * Internal function
+ */
 static inline u32
 f_free_count (svm_fifo_t * f, u32 head, u32 tail)
 {
   return (f->nitems + head - tail);
 }
 
-/* internal function */
+/**
+ * Fifo current size, i.e., number of bytes enqueued
+ *
+ * Internal function.
+ */
 static inline u32
 f_cursize (svm_fifo_t * f, u32 head, u32 tail)
 {
   return (f->nitems - f_free_count (f, head, tail));
 }
 
-/* used by consumer */
+/**
+ * Distance to a from b, i.e., a - b in the fifo
+ *
+ * Internal function.
+ */
+static inline u32
+f_distance_to (svm_fifo_t * f, u32 a, u32 b)
+{
+  return ((f->size + a - b) % f->size);
+}
+
+/**
+ * Distance from a to b, i.e., b - a in the fifo
+ *
+ * Internal function.
+ */
+static inline u32
+f_distance_from (svm_fifo_t * f, u32 a, u32 b)
+{
+  return ((f->size + b - a) % f->size);
+}
+
+/**
+ * Create fifo of requested size
+ *
+ * Allocates fifo on current heap.
+ *
+ * @param size		data size in bytes for fifo to be allocated. Will be
+ * 			rounded to the next highest power-of-two value.
+ * @return 		pointer to new fifo
+ */
+svm_fifo_t *svm_fifo_create (u32 size);
+/**
+ * Initialize fifo
+ *
+ * @param size		size for fifo
+ */
+void svm_fifo_init (svm_fifo_t * f, u32 size);
+/**
+ * Allocate a fifo chunk on heap
+ *
+ * If the chunk is allocated on a fifo segment, this should be called
+ * with the segment's heap pushed.
+ *
+ * @param size	chunk size in bytes. Will be rounded to the next highest
+ * 		power-of-two
+ * @return	new chunk or 0 if alloc failed
+ */
+svm_fifo_chunk_t *svm_fifo_chunk_alloc (u32 size);
+/**
+ * Grow fifo size by adding chunk to chunk list
+ *
+ * If fifos are allocated on a segment, this should be called with
+ * the segment's heap pushed.
+ *
+ * @param f	fifo to be extended
+ * @param c 	chunk or linked list of chunks to be added
+ */
+void svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c);
+/**
+ * Free fifo and associated state
+ *
+ * @param f	fifo
+ */
+void svm_fifo_free (svm_fifo_t * f);
+/**
+ * Cleanup fifo chunk lookup rb tree
+ *
+ * The rb tree is allocated in segment heap so this should be called
+ * with it pushed.
+ *
+ * @param f 	fifo to cleanup
+ */
+void svm_fifo_free_chunk_lookup (svm_fifo_t * f);
+/**
+ * Cleanup fifo ooo data
+ *
+ * The ooo data is allocated in producer process memory. The fifo
+ * segment heap should not be pushed.
+ *
+ * @param f	fifo to cleanup
+ */
+void svm_fifo_free_ooo_data (svm_fifo_t * f);
+/**
+ * Init fifo head and tail
+ *
+ * @param f	fifo
+ * @param head	head value that will be matched to a chunk
+ * @param tail	tail value that will be matched to a chunk
+ */
+void svm_fifo_init_pointers (svm_fifo_t * f, u32 head, u32 tail);
+/**
+ * Clone fifo
+ *
+ * Clones single/default chunk fifo. It does not work for fifos with
+ * multiple chunks.
+ */
+void svm_fifo_clone (svm_fifo_t * df, svm_fifo_t * sf);
+/**
+ * Enqueue data to fifo
+ *
+ * Data is enqueued and tail pointer is updated atomically. If the new data
+ * enqueued partly overlaps or "touches" an out-of-order segment, said segment
+ * is "consumed" and the number of bytes returned is appropriately updated.
+ *
+ * @param f	fifo
+ * @param len	length of data to copy
+ * @param src	buffer from where to copy the data
+ * @return	number of contiguous bytes that can be consumed or error
+ */
+int svm_fifo_enqueue (svm_fifo_t * f, u32 len, const u8 * src);
+/**
+ * Enqueue data to fifo with offset
+ *
+ * Data is enqueued without updating tail pointer. Instead, an out-of-order
+ * list of segments is generated and maintained. Fifo takes care of coalescing
+ * contiguous or overlapping segments.
+ *
+ * @param f		fifo
+ * @param offset	offset at which to copy the data
+ * @param len		len of data to copy
+ * @param src		buffer from where to copy the data
+ * @return		0 if enqueue was successful, error otherwise
+ */
+int svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset, u32 len,
+				  u8 * src);
+/**
+ * Overwrite fifo head with new data
+ *
+ * This should be typically used by dgram transport protocols that need
+ * to update the dgram header after dequeueing a chunk of data. It assumes
+ * that the dgram header is at most spread over two chunks.
+ *
+ * @param f		fifo
+ * @param src		src of new data
+ * @param len		length of new data
+ */
+void svm_fifo_overwrite_head (svm_fifo_t * f, u8 * src, u32 len);
+/**
+ * Dequeue data from fifo
+ *
+ * Data is dequeued to consumer provided buffer and head is atomically
+ * updated.
+ *
+ * @param f		fifo
+ * @param len		length of data to dequeue
+ * @param dst		buffer to where to dequeue the data
+ * @return		number of bytes dequeued or error
+ */
+int svm_fifo_dequeue (svm_fifo_t * f, u32 len, u8 * dst);
+/**
+ * Peek data from fifo
+ *
+ * Data is copied from requested offset into provided dst buffer. Head is
+ * not updated.
+ *
+ * @param f		fifo
+ * @param offset	offset from which to copy the data
+ * @param len		length of data to copy
+ * @param dst		buffer to where to dequeue the data
+ * @return		number of bytes peeked
+ */
+int svm_fifo_peek (svm_fifo_t * f, u32 offset, u32 len, u8 * dst);
+/**
+ * Dequeue and drop bytes from fifo
+ *
+ * Advances fifo head by requested amount of bytes.
+ *
+ * @param f		fifo
+ * @param len		number of bytes to drop
+ * @return		number of bytes dropped
+ */
+int svm_fifo_dequeue_drop (svm_fifo_t * f, u32 len);
+/**
+ * Dequeue and drop all bytes from fifo
+ *
+ * Advances head to tail position.
+ *
+ * @param f		fifo
+ */
+void svm_fifo_dequeue_drop_all (svm_fifo_t * f);
+int 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);
+/**
+ * Add io events subscriber to list
+ *
+ * @param f	fifo
+ * @param sub	subscriber opaque index (typically app worker index)
+ */
+void svm_fifo_add_subscriber (svm_fifo_t * f, u8 sub);
+/**
+ * Remove io events subscriber form list
+ *
+ * @param f	fifo
+ * @param sub	subscriber index to be removed
+ */
+void svm_fifo_del_subscriber (svm_fifo_t * f, u8 subscriber);
+/**
+ * Number of out-of-order segments for fifo
+ *
+ * @param f	fifo
+ * @return	number of out of order segments
+ */
+u32 svm_fifo_n_ooo_segments (svm_fifo_t * f);
+/*
+ * First out-of-order segment for fifo
+ *
+ * @param f	fifo
+ * @return	first out-of-order segment for fifo
+ */
+ooo_segment_t *svm_fifo_first_ooo_segment (svm_fifo_t * f);
+format_function_t format_svm_fifo;
+
+/**
+ * Fifo max bytes to dequeue optimized for consumer
+ *
+ * @param f	fifo
+ * @return	max number of bytes that can be dequeued
+ */
 static inline u32
 svm_fifo_max_dequeue_cons (svm_fifo_t * f)
 {
@@ -201,7 +434,12 @@ svm_fifo_max_dequeue_cons (svm_fifo_t * f)
   return f_cursize (f, head, tail);
 }
 
-/* used by producer*/
+/**
+ * Fifo max bytes to dequeue optimized for producer
+ *
+ * @param f	fifo
+ * @return	max number of bytes that can be dequeued
+ */
 static inline u32
 svm_fifo_max_dequeue_prod (svm_fifo_t * f)
 {
@@ -210,9 +448,12 @@ svm_fifo_max_dequeue_prod (svm_fifo_t * f)
   return f_cursize (f, head, tail);
 }
 
-/* use producer or consumer specific functions for perfomance.
- * svm_fifo_max_dequeue_cons (svm_fifo_t *f)
- * svm_fifo_max_dequeue_prod (svm_fifo_t *f)
+/**
+ * Fifo max bytes to dequeue
+ *
+ * Note: use producer or consumer specific functions for performance:
+ * @ref svm_fifo_max_dequeue_cons (svm_fifo_t *f)
+ * @ref svm_fifo_max_dequeue_prod (svm_fifo_t *f)
  */
 static inline u32
 svm_fifo_max_dequeue (svm_fifo_t * f)
@@ -222,15 +463,22 @@ svm_fifo_max_dequeue (svm_fifo_t * f)
   return f_cursize (f, head, tail);
 }
 
-/* used by producer */
+/**
+ * Check if fifo is full optimized for producer
+ *
+ * @param f	fifo
+ * @return	1 if fifo is full 0 otherwise
+ */
 static inline int
 svm_fifo_is_full_prod (svm_fifo_t * f)
 {
   return (svm_fifo_max_dequeue_prod (f) == f->nitems);
 }
 
-/* use producer or consumer specific functions for perfomance.
- * svm_fifo_is_full_prod (svm_fifo_t * f)
+/* Check if fifo is full.
+ *
+ * Note: use producer or consumer specific functions for performance.
+ * @ref svm_fifo_is_full_prod (svm_fifo_t * f)
  * add cons version if needed
  */
 static inline int
@@ -239,23 +487,36 @@ svm_fifo_is_full (svm_fifo_t * f)
   return (svm_fifo_max_dequeue (f) == f->nitems);
 }
 
-/* used by consumer */
+/**
+ * Check if fifo is empty optimized for consumer
+ *
+ * @param f 	fifo
+ * @return	1 if fifo is empty 0 otherwise
+ */
 static inline int
 svm_fifo_is_empty_cons (svm_fifo_t * f)
 {
   return (svm_fifo_max_dequeue_cons (f) == 0);
 }
 
-/* used by producer */
+/**
+ * Check if fifo is empty optimized for producer
+ *
+ * @param f	fifo
+ * @return	1 if fifo is empty 0 otherwise
+ */
 static inline int
 svm_fifo_is_empty_prod (svm_fifo_t * f)
 {
   return (svm_fifo_max_dequeue_prod (f) == 0);
 }
 
-/* use producer or consumer specific functions for perfomance.
- * svm_fifo_is_empty_cons (svm_fifo_t * f)
- * svm_fifo_is_empty_prod (svm_fifo_t * f)
+/**
+ * Check if fifo is empty
+ *
+ * Note: use producer or consumer specific functions for perfomance.
+ * @ref svm_fifo_is_empty_cons (svm_fifo_t * f)
+ * @ref svm_fifo_is_empty_prod (svm_fifo_t * f)
  */
 static inline int
 svm_fifo_is_empty (svm_fifo_t * f)
@@ -263,6 +524,12 @@ svm_fifo_is_empty (svm_fifo_t * f)
   return (svm_fifo_max_dequeue (f) == 0);
 }
 
+/**
+ * Check if fifo is wrapped
+ *
+ * @param f	fifo
+ * @return 	1 if 'normalized' head is ahead of tail
+ */
 static inline u8
 svm_fifo_is_wrapped (svm_fifo_t * f)
 {
@@ -271,7 +538,14 @@ svm_fifo_is_wrapped (svm_fifo_t * f)
   return head % f->size > tail % f->size;
 }
 
-/* used by producer*/
+/**
+ * Maximum number of bytes that can be enqueued into fifo
+ *
+ * Optimized for producer
+ *
+ * @param f	fifo
+ * @return	max number of bytes that can be enqueued into fifo
+ */
 static inline u32
 svm_fifo_max_enqueue_prod (svm_fifo_t * f)
 {
@@ -280,8 +554,10 @@ svm_fifo_max_enqueue_prod (svm_fifo_t * f)
   return f_free_count (f, head, tail);
 }
 
-/* use producer or consumer specfic functions for perfomance.
- * svm_fifo_max_enqueue_prod (svm_fifo_t *f)
+/* Maximum number of bytes that can be enqueued into fifo
+ *
+ * Note: use producer or consumer specific functions for performance.
+ * @ref svm_fifo_max_enqueue_prod (svm_fifo_t *f)
  * add consumer specific version if needed.
  */
 static inline u32
@@ -292,111 +568,10 @@ svm_fifo_max_enqueue (svm_fifo_t * f)
   return f_free_count (f, head, tail);
 }
 
-static inline int
-svm_fifo_has_event (svm_fifo_t * f)
-{
-  return f->has_event;
-}
-
-static inline u8
-svm_fifo_has_ooo_data (svm_fifo_t * f)
-{
-  return f->ooos_list_head != OOO_SEGMENT_INVALID_INDEX;
-}
-
-/**
- * Sets fifo event flag.
- *
- * Also acts as a release ordering.
- *
- * @return 1 if flag was not set.
- */
-always_inline u8
-svm_fifo_set_event (svm_fifo_t * f)
-{
-  /* return __sync_lock_test_and_set (&f->has_event, 1) == 0;
-     return __sync_bool_compare_and_swap (&f->has_event, 0, 1); */
-  return !clib_atomic_swap_rel_n (&f->has_event, 1);
-}
-
-/**
- * Unsets fifo event flag.
- *
- * Also acts as an acquire barrier.
- */
-always_inline void
-svm_fifo_unset_event (svm_fifo_t * f)
-{
-  clib_atomic_swap_acq_n (&f->has_event, 0);
-}
-
-svm_fifo_t *svm_fifo_create (u32 data_size_in_bytes);
-void svm_fifo_init (svm_fifo_t * f, u32 size);
-
-/**
- * Allocate a fifo chunk on heap
- *
- * If the chunk is allocated on a fifo segment, this should be called
- * with the segment's heap pushed.
- *
- * @param size	chunk size in bytes. Will be rounded to the next highest
- * 		power-of-two
- * @return	new chunk or 0 if alloc failed
- */
-svm_fifo_chunk_t *svm_fifo_chunk_alloc (u32 size);
-
-/**
- * Grow fifo size by adding chunk to chunk list
- *
- * If fifos are allocated on a segment, this should be called with
- * the segment's heap pushed.
- *
- * @param f	fifo to be extended
- * @param c 	chunk or linked list of chunks to be added
- */
-void svm_fifo_add_chunk (svm_fifo_t * f, svm_fifo_chunk_t * c);
-void svm_fifo_free (svm_fifo_t * f);
-/**
- * Cleanup fifo chunk lookup rb tree
- *
- * The rb tree is allocated in segment heap so this should be called
- * with it pushed.
- *
- * @param f 	fifo to cleanup
- */
-void svm_fifo_free_chunk_lookup (svm_fifo_t * f);
-/**
- * Cleanup fifo ooo data
- *
- * The ooo data is allocated in producer process memory. The fifo
- * segment heap should not be pushed.
- *
- * @param f	fifo to cleanup
- */
-void svm_fifo_free_ooo_data (svm_fifo_t * f);
-
-int svm_fifo_enqueue_nowait (svm_fifo_t * f, u32 max_bytes,
-			     const u8 * copy_from_here);
-int svm_fifo_enqueue_with_offset (svm_fifo_t * f, u32 offset,
-				  u32 required_bytes, u8 * copy_from_here);
-int svm_fifo_dequeue_nowait (svm_fifo_t * f, u32 max_bytes, u8 * copy_here);
-
-int svm_fifo_peek (svm_fifo_t * f, u32 offset, u32 max_bytes, u8 * copy_here);
-int svm_fifo_dequeue_drop (svm_fifo_t * f, u32 max_bytes);
-void svm_fifo_dequeue_drop_all (svm_fifo_t * f);
-int 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);
-void svm_fifo_init_pointers (svm_fifo_t * f, u32 head, u32 tail);
-void svm_fifo_clone (svm_fifo_t * df, svm_fifo_t * sf);
-void svm_fifo_overwrite_head (svm_fifo_t * f, u8 * data, u32 len);
-void svm_fifo_add_subscriber (svm_fifo_t * f, u8 subscriber);
-void svm_fifo_del_subscriber (svm_fifo_t * f, u8 subscriber);
-format_function_t format_svm_fifo;
-
 /**
  * Max contiguous chunk of data that can be read
  */
-always_inline u32
+static inline u32
 svm_fifo_max_read_chunk (svm_fifo_t * f)
 {
   u32 head, tail;
@@ -410,7 +585,7 @@ svm_fifo_max_read_chunk (svm_fifo_t * f)
 /**
  * Max contiguous chunk of data that can be written
  */
-always_inline u32
+static inline u32
 svm_fifo_max_write_chunk (svm_fifo_t * f)
 {
   u32 head, tail;
@@ -425,19 +600,22 @@ svm_fifo_max_write_chunk (svm_fifo_t * f)
  * Advance tail pointer
  *
  * Useful for moving tail pointer after external enqueue.
+ *
+ * @param f		fifo
+ * @param len		number of bytes to add to tail
  */
-always_inline void
-svm_fifo_enqueue_nocopy (svm_fifo_t * f, u32 bytes)
+static inline void
+svm_fifo_enqueue_nocopy (svm_fifo_t * f, u32 len)
 {
-  ASSERT (bytes <= svm_fifo_max_enqueue_prod (f));
+  ASSERT (len <= svm_fifo_max_enqueue_prod (f));
   /* load-relaxed: producer owned index */
   u32 tail = f->tail;
-  tail += bytes;
+  tail += len;
   /* store-rel: producer owned index (paired with load-acq in consumer) */
   clib_atomic_store_rel_n (&f->tail, tail);
 }
 
-always_inline u8 *
+static inline u8 *
 svm_fifo_head (svm_fifo_t * f)
 {
   /* load-relaxed: consumer owned index */
@@ -445,7 +623,7 @@ svm_fifo_head (svm_fifo_t * f)
 	  + ((f->head % f->size) - f->head_chunk->start_byte));
 }
 
-always_inline u8 *
+static inline u8 *
 svm_fifo_tail (svm_fifo_t * f)
 {
   /* load-relaxed: producer owned index */
@@ -453,18 +631,132 @@ svm_fifo_tail (svm_fifo_t * f)
 	  + ((f->tail % f->size) - f->tail_chunk->start_byte));
 }
 
+static inline u8
+svm_fifo_n_subscribers (svm_fifo_t * f)
+{
+  return f->n_subscribers;
+}
+
+/**
+ * Check if fifo has out-of-order data
+ *
+ * @param f	fifo
+ * @return	1 if fifo has ooo data, 0 otherwise
+ */
+static inline u8
+svm_fifo_has_ooo_data (svm_fifo_t * f)
+{
+  return f->ooos_list_head != OOO_SEGMENT_INVALID_INDEX;
+}
+
+static inline ooo_segment_t *
+svm_fifo_newest_ooo_segment (svm_fifo_t * f)
+{
+  if (f->ooos_newest == OOO_SEGMENT_INVALID_INDEX)
+    return 0;
+  return pool_elt_at_index (f->ooo_segments, f->ooos_newest);
+}
+
+static inline void
+svm_fifo_newest_ooo_segment_reset (svm_fifo_t * f)
+{
+  f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
+}
+
+static inline u32
+ooo_segment_offset_prod (svm_fifo_t * f, ooo_segment_t * s)
+{
+  u32 tail;
+  /* load-relaxed: producer owned index */
+  tail = f->tail;
+
+  return f_distance_to (f, s->start, tail);
+}
+
+static inline u32
+ooo_segment_length (svm_fifo_t * f, ooo_segment_t * s)
+{
+  return s->length;
+}
+
+/**
+ * Check if fifo has io event
+ *
+ * @param f	fifo
+ * @return	1 if fifo has event, 0 otherwise
+ */
+static inline int
+svm_fifo_has_event (svm_fifo_t * f)
+{
+  return f->has_event;
+}
+
+/**
+ * Set fifo event flag.
+ *
+ * Forces release semantics.
+ *
+ * @param f	fifo
+ * @return 	1 if flag was not set, 0 otherwise
+ */
+always_inline u8
+svm_fifo_set_event (svm_fifo_t * f)
+{
+  return !clib_atomic_swap_rel_n (&f->has_event, 1);
+}
+
+/**
+ * Unset fifo event flag.
+ *
+ * Forces acquire semantics
+ *
+ * @param f	fifo
+ */
+always_inline void
+svm_fifo_unset_event (svm_fifo_t * f)
+{
+  clib_atomic_swap_acq_n (&f->has_event, 0);
+}
+
+/**
+ * Set specific want tx notification flag
+ *
+ * For list of flags see @ref svm_fifo_tx_ntf_t
+ *
+ * @param f		fifo
+ * @param ntf_type	type of notification requested
+ */
 static inline void
 svm_fifo_add_want_tx_ntf (svm_fifo_t * f, u8 ntf_type)
 {
   f->want_tx_ntf |= ntf_type;
 }
 
+/**
+ * Clear specific want tx notification flag
+ *
+ * For list of flags see @ref svm_fifo_tx_ntf_t
+ *
+ * @param f 		fifo
+ * @param ntf_type	type of notification to be cleared
+ */
 static inline void
 svm_fifo_del_want_tx_ntf (svm_fifo_t * f, u8 ntf_type)
 {
   f->want_tx_ntf &= ~ntf_type;
 }
 
+/**
+ * Clear the want tx notification flag and set has tx notification
+ *
+ * Should be used after enqueuing a tx event. This clears the
+ * SVM_FIFO_WANT_TX_NOTIF flag but it does not clear
+ * SVM_FIFO_WANT_TX_NOTIF_IF_FULL. If the latter was set, has_tx_ntf is
+ * set to avoid enqueueing tx events for for all dequeue operations until
+ * it is manually cleared.
+ *
+ * @param f	fifo
+ */
 static inline void
 svm_fifo_clear_tx_ntf (svm_fifo_t * f)
 {
@@ -473,12 +765,31 @@ svm_fifo_clear_tx_ntf (svm_fifo_t * f)
   svm_fifo_del_want_tx_ntf (f, SVM_FIFO_WANT_TX_NOTIF);
 }
 
+/**
+ * Clear has tx notification flag
+ *
+ * The fifo generates only one event per SVM_FIFO_WANT_TX_NOTIF_IF_FULL
+ * request and sets has_tx_ntf. To received new events the flag must be
+ * cleared using this function.
+ *
+ * @param f	fifo
+ */
 static inline void
 svm_fifo_reset_tx_ntf (svm_fifo_t * f)
 {
   f->has_tx_ntf = 0;
 }
 
+/**
+ * Check if fifo needs tx notification
+ *
+ * Determines based on tx notification request flags and state of the fifo if
+ * a tx io event should be generated.
+ *
+ * @param f		fifo
+ * @param n_last_deq	number of bytes last dequeued
+ * @return		1 if tx io event should be generated, 0 otherwise
+ */
 static inline u8
 svm_fifo_needs_tx_ntf (svm_fifo_t * f, u32 n_last_deq)
 {
@@ -501,73 +812,6 @@ svm_fifo_needs_tx_ntf (svm_fifo_t * f, u32 n_last_deq)
   return 0;
 }
 
-always_inline u8
-svm_fifo_n_subscribers (svm_fifo_t * f)
-{
-  return f->n_subscribers;
-}
-
-u32 svm_fifo_number_ooo_segments (svm_fifo_t * f);
-ooo_segment_t *svm_fifo_first_ooo_segment (svm_fifo_t * f);
-
-always_inline ooo_segment_t *
-svm_fifo_newest_ooo_segment (svm_fifo_t * f)
-{
-  if (f->ooos_newest == OOO_SEGMENT_INVALID_INDEX)
-    return 0;
-  return pool_elt_at_index (f->ooo_segments, f->ooos_newest);
-}
-
-always_inline void
-svm_fifo_newest_ooo_segment_reset (svm_fifo_t * f)
-{
-  f->ooos_newest = OOO_SEGMENT_INVALID_INDEX;
-}
-
-always_inline u32
-ooo_segment_distance_from_tail (svm_fifo_t * f, u32 pos, u32 tail)
-{
-  return ((f->size + pos - tail) % f->size);
-}
-
-always_inline u32
-ooo_segment_distance_to_tail (svm_fifo_t * f, u32 pos, u32 tail)
-{
-  return ((f->size + tail - pos) % f->size);
-}
-
-always_inline u32
-ooo_segment_offset_prod (svm_fifo_t * f, ooo_segment_t * s)
-{
-  u32 tail;
-  /* load-relaxed: producer owned index */
-  tail = f->tail;
-
-  return ooo_segment_distance_from_tail (f, s->start, tail);
-}
-
-always_inline u32
-ooo_segment_length (svm_fifo_t * f, ooo_segment_t * s)
-{
-  return s->length;
-}
-
-always_inline ooo_segment_t *
-ooo_segment_get_prev (svm_fifo_t * f, ooo_segment_t * s)
-{
-  if (s->prev == OOO_SEGMENT_INVALID_INDEX)
-    return 0;
-  return pool_elt_at_index (f->ooo_segments, s->prev);
-}
-
-always_inline ooo_segment_t *
-ooo_segment_next (svm_fifo_t * f, ooo_segment_t * s)
-{
-  if (s->next == OOO_SEGMENT_INVALID_INDEX)
-    return 0;
-  return pool_elt_at_index (f->ooo_segments, s->next);
-}
-
 #endif /* __included_ssvm_fifo_h__ */
 
 /*