ck_ring: Add *_size_* ck_ring enqueue operations.

These variants of ck_ring_enqueue_* return the snapshot of queue
length with respect to the linearization point. This can be used to
extract ring size without incurring additional cacheline invalidation
overhead from the writer.

include/ck_ring.h

@@ -75,6 +75,27 @@
 		return ring->size;						\
 	}									\
 	CK_CC_INLINE static bool						\
+	ck_ring_enqueue_spsc_size_##name(struct ck_ring_##name *ring,		\
+	    struct type *entry,							\
+	    unsigned int *size)							\
+	{									\
+		unsigned int consumer, producer, delta;				\
+		unsigned int mask = ring->mask;					\
+										\
+		consumer = ck_pr_load_uint(&ring->c_head);			\
+		producer = ring->p_tail;					\
+		delta = producer + 1;						\
+		*size = (producer - consumer) & mask;				\
+										\
+		if ((delta & mask) == (consumer & mask))			\
+			return false;						\
+										\
+		ring->ring[producer & mask] = *entry;				\
+		ck_pr_fence_store();						\
+		ck_pr_store_uint(&ring->p_tail, delta);				\
+		return true;							\
+	}									\
+	CK_CC_INLINE static bool						\
 	ck_ring_enqueue_spsc_##name(struct ck_ring_##name *ring,		\
 				    struct type *entry)				\
 	{									\
@@ -114,6 +135,13 @@
 		return true;							\
 	}									\
 	CK_CC_INLINE static bool						\
+	ck_ring_enqueue_spmc_size_##name(struct ck_ring_##name *ring,		\
+	    void *entry, unsigned int *size)					\
+	{									\
+										\
+		return ck_ring_enqueue_spsc_size_##name(ring, entry, size);	\
+	}									\
+	CK_CC_INLINE static bool						\
 	ck_ring_enqueue_spmc_##name(struct ck_ring_##name *ring, void *entry)	\
 	{									\
 										\
@@ -217,6 +245,50 @@ ck_ring_capacity(struct ck_ring *ring)
 	return ring->size;
 }
 
+/*
+ * Atomically enqueues the specified entry. Returns true on success, returns
+ * false if the ck_ring is full. This operation only support one active
+ * invocation at a time and works in the presence of a concurrent invocation
+ * of ck_ring_dequeue_spsc.
+ *
+ * This variant of ck_ring_enqueue_spsc returns the snapshot of queue length
+ * with respect to the linearization point. This can be used to extract ring
+ * size without incurring additional cacheline invalidation overhead from the
+ * writer.
+ */
+CK_CC_INLINE static bool
+ck_ring_enqueue_spsc_size(struct ck_ring *ring,
+    void *entry,
+    unsigned int *size)
+{
+	unsigned int consumer, producer, delta;
+	unsigned int mask = ring->mask;
+
+	consumer = ck_pr_load_uint(&ring->c_head);
+	producer = ring->p_tail;
+	delta = producer + 1;
+	*size = (producer - consumer) & mask;
+
+	if ((delta & mask) == (consumer & mask))
+		return false;
+
+	ring->ring[producer & mask] = entry;
+
+	/*
+	 * Make sure to update slot value before indicating
+	 * that the slot is available for consumption.
+	 */
+	ck_pr_fence_store();
+	ck_pr_store_uint(&ring->p_tail, delta);
+	return true;
+}
+
+/*
+ * Atomically enqueues the specified entry. Returns true on success, returns
+ * false if the ck_ring is full. This operation only support one active
+ * invocation at a time and works in the presence of a concurrent invocation
+ * of ck_ring_dequeue_spsc.
+ */
 CK_CC_INLINE static bool
 ck_ring_enqueue_spsc(struct ck_ring *ring, void *entry)
 {
@@ -275,6 +347,32 @@ ck_ring_dequeue_spsc(struct ck_ring *ring, void *data)
 	return true;
 }
 
+/*
+ * Atomically enqueues the specified entry. Returns true on success, returns
+ * false if the ck_ring is full. This operation only support one active
+ * invocation at a time and works in the presence of up to UINT_MAX concurrent
+ * invocations of ck_ring_dequeue_spmc.
+ *
+ * This variant of ck_ring_enqueue_spmc returns the snapshot of queue length
+ * with respect to the linearization point. This can be used to extract ring
+ * size without incurring additional cacheline invalidation overhead from the
+ * writer.
+ */
+CK_CC_INLINE static bool
+ck_ring_enqueue_spmc_size(struct ck_ring *ring,
+    void *entry,
+    unsigned int *size)
+{
+
+	return ck_ring_enqueue_spsc_size(ring, entry, size);
+}
+
+/*
+ * Atomically enqueues the specified entry. Returns true on success, returns
+ * false if the ck_ring is full. This operation only support one active
+ * invocation at a time and works in the presence of up to UINT_MAX concurrent
+ * invocations of ck_ring_dequeue_spmc.
+ */
 CK_CC_INLINE static bool
 ck_ring_enqueue_spmc(struct ck_ring *ring, void *entry)
 {