[dpdk-dev] [RFC v2 1/1] lib/ring: add scatter gather APIs

[Honnappa Nagarahalli]

Add scatter gather APIs to avoid intermediate memcpy. Use cases
that involve copying large amount of data to/from the ring
can benefit from these APIs.

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
---
 lib/librte_ring/meson.build        |   3 +-
 lib/librte_ring/rte_ring_elem.h    |   1 +
 lib/librte_ring/rte_ring_peek_sg.h | 552 +++++++++++++++++++++++++++++
 3 files changed, 555 insertions(+), 1 deletion(-)
 create mode 100644 lib/librte_ring/rte_ring_peek_sg.h

diff --git a/lib/librte_ring/meson.build b/lib/librte_ring/meson.build
index 31c0b4649..377694713 100644
--- a/lib/librte_ring/meson.build
+++ b/lib/librte_ring/meson.build
@@ -12,4 +12,5 @@ headers = files('rte_ring.h',
 		'rte_ring_peek.h',
 		'rte_ring_peek_c11_mem.h',
 		'rte_ring_rts.h',
-		'rte_ring_rts_c11_mem.h')
+		'rte_ring_rts_c11_mem.h',
+		'rte_ring_peek_sg.h')
diff --git a/lib/librte_ring/rte_ring_elem.h b/lib/librte_ring/rte_ring_elem.h
index 938b398fc..7d3933f15 100644
--- a/lib/librte_ring/rte_ring_elem.h
+++ b/lib/librte_ring/rte_ring_elem.h
@@ -1079,6 +1079,7 @@ rte_ring_dequeue_burst_elem(struct rte_ring *r, void *obj_table,
 
 #ifdef ALLOW_EXPERIMENTAL_API
 #include <rte_ring_peek.h>
+#include <rte_ring_peek_sg.h>
 #endif
 
 #include <rte_ring.h>
diff --git a/lib/librte_ring/rte_ring_peek_sg.h b/lib/librte_ring/rte_ring_peek_sg.h
new file mode 100644
index 000000000..97d5764a6
--- /dev/null
+++ b/lib/librte_ring/rte_ring_peek_sg.h
@@ -0,0 +1,552 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright (c) 2020 Arm
+ * Copyright (c) 2007-2009 Kip Macy kmacy at freebsd.org
+ * All rights reserved.
+ * Derived from FreeBSD's bufring.h
+ * Used as BSD-3 Licensed with permission from Kip Macy.
+ */
+
+#ifndef _RTE_RING_PEEK_SG_H_
+#define _RTE_RING_PEEK_SG_H_
+
+/**
+ * @file
+ * @b EXPERIMENTAL: this API may change without prior notice
+ * It is not recommended to include this file directly.
+ * Please include <rte_ring_elem.h> instead.
+ *
+ * Ring Peek Scatter Gather APIs
+ * Introduction of rte_ring with scatter gather serialized producer/consumer
+ * (HTS sync mode) makes it possible to split public enqueue/dequeue API
+ * into 3 phases:
+ * - enqueue/dequeue start
+ * - copy data to/from the ring
+ * - enqueue/dequeue finish
+ * Along with the advantages of the peek APIs, these APIs provide the ability
+ * to avoid copying of the data to temporary area.
+ *
+ * Note that right now this new API is available only for two sync modes:
+ * 1) Single Producer/Single Consumer (RTE_RING_SYNC_ST)
+ * 2) Serialized Producer/Serialized Consumer (RTE_RING_SYNC_MT_HTS).
+ * It is a user responsibility to create/init ring with appropriate sync
+ * modes selected.
+ *
+ * Example usage:
+ * // read 1 elem from the ring:
+ * n = rte_ring_enqueue_sg_bulk_start(ring, 32, &sgd, NULL);
+ * if (n != 0) {
+ *	//Copy objects in the ring
+ *	memcpy (sgd->ptr1, obj, sgd->n1 * sizeof(uintptr_t));
+ *	if (n != sgd->n1)
+ *		//Second memcpy because of wrapround
+ *		n2 = n - sgd->n1;
+ *		memcpy (sgd->ptr2, obj[n2], n2 * sizeof(uintptr_t));
+ *	rte_ring_dequeue_sg_finish(ring, n);
+ * }
+ *
+ * Note that between _start_ and _finish_ none other thread can proceed
+ * with enqueue(/dequeue) operation till _finish_ completes.
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <rte_ring_peek_c11_mem.h>
+
+/* Rock that needs to be passed between reserve and commit APIs */
+struct rte_ring_sg_data {
+	/* Pointer to the first space in the ring */
+	void **ptr1;
+	/* Pointer to the second space in the ring if there is wrap-around */
+	void **ptr2;
+	/* Number of elements in the first pointer. If this is equal to
+	 * the number of elements requested, then ptr2 is NULL.
+	 * Otherwise, subtracting n1 from number of elements requested
+	 * will give the number of elements available at ptr2.
+	 */
+	unsigned int n1;
+};
+
+static __rte_always_inline void
+__rte_ring_get_elem_addr_64(struct rte_ring *r, uint32_t head,
+	uint32_t num, void **dst1, uint32_t *n1, void **dst2)
+{
+	uint32_t idx = head & r->mask;
+	uint64_t *ring = (uint64_t *)&r[1];
+
+	*dst1 = ring + idx;
+	*n1 = num;
+
+	if (idx + num > r->size) {
+		*n1 = num - (r->size - idx - 1);
+		*dst2 = ring;
+	}
+}
+
+static __rte_always_inline void
+__rte_ring_get_elem_addr_128(struct rte_ring *r, uint32_t head,
+	uint32_t num, void **dst1, uint32_t *n1, void **dst2)
+{
+	uint32_t idx = head & r->mask;
+	rte_int128_t *ring = (rte_int128_t *)&r[1];
+
+	*dst1 = ring + idx;
+	*n1 = num;
+
+	if (idx + num > r->size) {
+		*n1 = num - (r->size - idx - 1);
+		*dst2 = ring;
+	}
+}
+
+static __rte_always_inline void
+__rte_ring_get_elem_addr(struct rte_ring *r, uint32_t head,
+	uint32_t esize, uint32_t num, void **dst1, uint32_t *n1, void **dst2)
+{
+	if (esize == 8)
+		__rte_ring_get_elem_addr_64(r, head,
+						num, dst1, n1, dst2);
+	else if (esize == 16)
+		__rte_ring_get_elem_addr_128(r, head,
+						num, dst1, n1, dst2);
+	else {
+		uint32_t idx, scale, nr_idx;
+		uint32_t *ring = (uint32_t *)&r[1];
+
+		/* Normalize to uint32_t */
+		scale = esize / sizeof(uint32_t);
+		idx = head & r->mask;
+		nr_idx = idx * scale;
+
+		*dst1 = ring + nr_idx;
+		*n1 = num;
+
+		if (idx + num > r->size) {
+			*n1 = num - (r->size - idx - 1);
+			*dst2 = ring;
+		}
+	}
+}
+
+/**
+ * @internal This function moves prod head value.
+ */
+static __rte_always_inline unsigned int
+__rte_ring_do_enqueue_sg_elem_start(struct rte_ring *r, unsigned int esize,
+		uint32_t n, enum rte_ring_queue_behavior behavior,
+		struct rte_ring_sg_data *sgd, unsigned int *free_space)
+{
+	uint32_t free, head, next;
+
+	switch (r->prod.sync_type) {
+	case RTE_RING_SYNC_ST:
+		n = __rte_ring_move_prod_head(r, RTE_RING_SYNC_ST, n,
+			behavior, &head, &next, &free);
+		__rte_ring_get_elem_addr(r, head, esize, n, (void **)&sgd->ptr1,
+			&sgd->n1, (void **)&sgd->ptr2);
+		break;
+	case RTE_RING_SYNC_MT_HTS:
+		n = __rte_ring_hts_move_prod_head(r, n, behavior, &head, &free);
+		__rte_ring_get_elem_addr(r, head, esize, n, (void **)&sgd->ptr1,
+			&sgd->n1, (void **)&sgd->ptr2);
+		break;
+	case RTE_RING_SYNC_MT:
+	case RTE_RING_SYNC_MT_RTS:
+	default:
+		/* unsupported mode, shouldn't be here */
+		RTE_ASSERT(0);
+		n = 0;
+		free = 0;
+	}
+
+	if (free_space != NULL)
+		*free_space = free - n;
+	return n;
+}
+
+/**
+ * Start to enqueue several objects on the ring.
+ * Note that no actual objects are put in the queue by this function,
+ * it just reserves space for the user on the ring.
+ * User has to copy objects into the queue using the returned pointers.
+ * User should call rte_ring_enqueue_sg_bulk_elem_finish to complete the
+ * enqueue operation.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param esize
+ *   The size of ring element, in bytes. It must be a multiple of 4.
+ * @param n
+ *   The number of objects to add in the ring.
+ * @param sgd
+ *   The scatter-gather data containing pointers for copying data.
+ * @param free_space
+ *   if non-NULL, returns the amount of space in the ring after the
+ *   reservation operation has finished.
+ * @return
+ *   The number of objects that can be enqueued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_enqueue_sg_bulk_elem_start(struct rte_ring *r, unsigned int esize,
+	unsigned int n, struct rte_ring_sg_data *sgd, unsigned int *free_space)
+{
+	return __rte_ring_do_enqueue_sg_elem_start(r, esize, n,
+			RTE_RING_QUEUE_FIXED, sgd, free_space);
+}
+
+/**
+ * Start to enqueue several pointers to objects on the ring.
+ * Note that no actual pointers are put in the queue by this function,
+ * it just reserves space for the user on the ring.
+ * User has to copy pointers to objects into the queue using the
+ * returned pointers.
+ * User should call rte_ring_enqueue_sg_bulk_finish to complete the
+ * enqueue operation.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param n
+ *   The number of objects to add in the ring.
+ * @param sgd
+ *   The scatter-gather data containing pointers for copying data.
+ * @param free_space
+ *   if non-NULL, returns the amount of space in the ring after the
+ *   reservation operation has finished.
+ * @return
+ *   The number of objects that can be enqueued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_enqueue_sg_bulk_start(struct rte_ring *r, unsigned int n,
+	struct rte_ring_sg_data *sgd, unsigned int *free_space)
+{
+	return rte_ring_enqueue_sg_bulk_elem_start(r, sizeof(uintptr_t), n,
+							sgd, free_space);
+}
+/**
+ * Start to enqueue several objects on the ring.
+ * Note that no actual objects are put in the queue by this function,
+ * it just reserves space for the user on the ring.
+ * User has to copy objects into the queue using the returned pointers.
+ * User should call rte_ring_enqueue_sg_bulk_elem_finish to complete the
+ * enqueue operation.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param esize
+ *   The size of ring element, in bytes. It must be a multiple of 4.
+ * @param n
+ *   The number of objects to add in the ring.
+ * @param sgd
+ *   The scatter-gather data containing pointers for copying data.
+ * @param free_space
+ *   if non-NULL, returns the amount of space in the ring after the
+ *   reservation operation has finished.
+ * @return
+ *   The number of objects that can be enqueued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_enqueue_sg_burst_elem_start(struct rte_ring *r, unsigned int esize,
+	unsigned int n, struct rte_ring_sg_data *sgd, unsigned int *free_space)
+{
+	return __rte_ring_do_enqueue_sg_elem_start(r, esize, n,
+			RTE_RING_QUEUE_VARIABLE, sgd, free_space);
+}
+
+/**
+ * Start to enqueue several pointers to objects on the ring.
+ * Note that no actual pointers are put in the queue by this function,
+ * it just reserves space for the user on the ring.
+ * User has to copy pointers to objects into the queue using the
+ * returned pointers.
+ * User should call rte_ring_enqueue_sg_bulk_finish to complete the
+ * enqueue operation.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param n
+ *   The number of objects to add in the ring.
+ * @param sgd
+ *   The scatter-gather data containing pointers for copying data.
+ * @param free_space
+ *   if non-NULL, returns the amount of space in the ring after the
+ *   reservation operation has finished.
+ * @return
+ *   The number of objects that can be enqueued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_enqueue_sg_burst_start(struct rte_ring *r, unsigned int n,
+	struct rte_ring_sg_data *sgd, unsigned int *free_space)
+{
+	return rte_ring_enqueue_sg_burst_elem_start(r, sizeof(uintptr_t), n,
+							sgd, free_space);
+}
+
+/**
+ * Complete enqueuing several objects on the ring.
+ * Note that number of objects to enqueue should not exceed previous
+ * enqueue_start return value.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param n
+ *   The number of objects to add to the ring.
+ */
+__rte_experimental
+static __rte_always_inline void
+rte_ring_enqueue_sg_elem_finish(struct rte_ring *r, unsigned int n)
+{
+	uint32_t tail;
+
+	switch (r->prod.sync_type) {
+	case RTE_RING_SYNC_ST:
+		n = __rte_ring_st_get_tail(&r->prod, &tail, n);
+		__rte_ring_st_set_head_tail(&r->prod, tail, n, 1);
+		break;
+	case RTE_RING_SYNC_MT_HTS:
+		n = __rte_ring_hts_get_tail(&r->hts_prod, &tail, n);
+		__rte_ring_hts_set_head_tail(&r->hts_prod, tail, n, 1);
+		break;
+	case RTE_RING_SYNC_MT:
+	case RTE_RING_SYNC_MT_RTS:
+	default:
+		/* unsupported mode, shouldn't be here */
+		RTE_ASSERT(0);
+	}
+}
+
+/**
+ * Complete enqueuing several pointers to objects on the ring.
+ * Note that number of objects to enqueue should not exceed previous
+ * enqueue_start return value.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param n
+ *   The number of pointers to objects to add to the ring.
+ */
+__rte_experimental
+static __rte_always_inline void
+rte_ring_enqueue_sg_finish(struct rte_ring *r, unsigned int n)
+{
+	rte_ring_enqueue_sg_elem_finish(r, n);
+}
+
+/**
+ * @internal This function moves cons head value and copies up to *n*
+ * objects from the ring to the user provided obj_table.
+ */
+static __rte_always_inline unsigned int
+__rte_ring_do_dequeue_sg_elem_start(struct rte_ring *r,
+	uint32_t esize, uint32_t n, enum rte_ring_queue_behavior behavior,
+	struct rte_ring_sg_data *sgd, unsigned int *available)
+{
+	uint32_t avail, head, next;
+
+	switch (r->cons.sync_type) {
+	case RTE_RING_SYNC_ST:
+		n = __rte_ring_move_cons_head(r, RTE_RING_SYNC_ST, n,
+			behavior, &head, &next, &avail);
+		__rte_ring_get_elem_addr(r, head, esize, n,
+					sgd->ptr1, &sgd->n1, sgd->ptr2);
+		break;
+	case RTE_RING_SYNC_MT_HTS:
+		n = __rte_ring_hts_move_cons_head(r, n, behavior,
+			&head, &avail);
+		__rte_ring_get_elem_addr(r, head, esize, n,
+					sgd->ptr1, &sgd->n1, sgd->ptr2);
+		break;
+	case RTE_RING_SYNC_MT:
+	case RTE_RING_SYNC_MT_RTS:
+	default:
+		/* unsupported mode, shouldn't be here */
+		RTE_ASSERT(0);
+		n = 0;
+		avail = 0;
+	}
+
+	if (available != NULL)
+		*available = avail - n;
+	return n;
+}
+
+/**
+ * Start to dequeue several objects from the ring.
+ * Note that no actual objects are copied from the queue by this function.
+ * User has to copy objects from the queue using the returned pointers.
+ * User should call rte_ring_dequeue_sg_bulk_elem_finish to complete the
+ * dequeue operation.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param esize
+ *   The size of ring element, in bytes. It must be a multiple of 4.
+ * @param n
+ *   The number of objects to remove from the ring.
+ * @param sgd
+ *   The scatter-gather data containing pointers for copying data.
+ * @param available
+ *   If non-NULL, returns the number of remaining ring entries after the
+ *   dequeue has finished.
+ * @return
+ *   The number of objects that can be dequeued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_dequeue_sg_bulk_elem_start(struct rte_ring *r, unsigned int esize,
+	unsigned int n, struct rte_ring_sg_data *sgd, unsigned int *available)
+{
+	return __rte_ring_do_dequeue_sg_elem_start(r, esize, n,
+			RTE_RING_QUEUE_FIXED, sgd, available);
+}
+
+/**
+ * Start to dequeue several pointers to objects from the ring.
+ * Note that no actual pointers are removed from the queue by this function.
+ * User has to copy pointers to objects from the queue using the
+ * returned pointers.
+ * User should call rte_ring_dequeue_sg_bulk_finish to complete the
+ * dequeue operation.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param n
+ *   The number of objects to remove from the ring.
+ * @param sgd
+ *   The scatter-gather data containing pointers for copying data.
+ * @param available
+ *   If non-NULL, returns the number of remaining ring entries after the
+ *   dequeue has finished.
+ * @return
+ *   The number of objects that can be dequeued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_dequeue_sg_bulk_start(struct rte_ring *r, unsigned int n,
+	struct rte_ring_sg_data *sgd, unsigned int *available)
+{
+	return rte_ring_dequeue_sg_bulk_elem_start(r, sizeof(uintptr_t),
+		n, sgd, available);
+}
+
+/**
+ * Start to dequeue several objects from the ring.
+ * Note that no actual objects are copied from the queue by this function.
+ * User has to copy objects from the queue using the returned pointers.
+ * User should call rte_ring_dequeue_sg_burst_elem_finish to complete the
+ * dequeue operation.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param esize
+ *   The size of ring element, in bytes. It must be a multiple of 4.
+ *   This must be the same value used while creating the ring. Otherwise
+ *   the results are undefined.
+ * @param n
+ *   The number of objects to dequeue from the ring.
+ * @param sgd
+ *   The scatter-gather data containing pointers for copying data.
+ * @param available
+ *   If non-NULL, returns the number of remaining ring entries after the
+ *   dequeue has finished.
+ * @return
+ *   The number of objects that can be dequeued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_dequeue_sg_burst_elem_start(struct rte_ring *r, unsigned int esize,
+	unsigned int n, struct rte_ring_sg_data *sgd, unsigned int *available)
+{
+	return __rte_ring_do_dequeue_sg_elem_start(r, esize, n,
+			RTE_RING_QUEUE_VARIABLE, sgd, available);
+}
+
+/**
+ * Start to dequeue several pointers to objects from the ring.
+ * Note that no actual pointers are removed from the queue by this function.
+ * User has to copy pointers to objects from the queue using the
+ * returned pointers.
+ * User should call rte_ring_dequeue_sg_burst_finish to complete the
+ * dequeue operation.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param n
+ *   The number of objects to remove from the ring.
+ * @param sgd
+ *   The scatter-gather data containing pointers for copying data.
+ * @param available
+ *   If non-NULL, returns the number of remaining ring entries after the
+ *   dequeue has finished.
+ * @return
+ *   The number of objects that can be dequeued, either 0 or n
+ */
+__rte_experimental
+static __rte_always_inline unsigned int
+rte_ring_dequeue_sg_burst_start(struct rte_ring *r, unsigned int n,
+		struct rte_ring_sg_data *sgd, unsigned int *available)
+{
+	return rte_ring_dequeue_sg_burst_elem_start(r, sizeof(uintptr_t), n,
+			sgd, available);
+}
+
+/**
+ * Complete dequeuing several objects from the ring.
+ * Note that number of objects to dequeued should not exceed previous
+ * dequeue_start return value.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param n
+ *   The number of objects to remove from the ring.
+ */
+__rte_experimental
+static __rte_always_inline void
+rte_ring_dequeue_sg_elem_finish(struct rte_ring *r, unsigned int n)
+{
+	uint32_t tail;
+
+	switch (r->cons.sync_type) {
+	case RTE_RING_SYNC_ST:
+		n = __rte_ring_st_get_tail(&r->cons, &tail, n);
+		__rte_ring_st_set_head_tail(&r->cons, tail, n, 0);
+		break;
+	case RTE_RING_SYNC_MT_HTS:
+		n = __rte_ring_hts_get_tail(&r->hts_cons, &tail, n);
+		__rte_ring_hts_set_head_tail(&r->hts_cons, tail, n, 0);
+		break;
+	case RTE_RING_SYNC_MT:
+	case RTE_RING_SYNC_MT_RTS:
+	default:
+		/* unsupported mode, shouldn't be here */
+		RTE_ASSERT(0);
+	}
+}
+
+/**
+ * Complete dequeuing several objects from the ring.
+ * Note that number of objects to dequeued should not exceed previous
+ * dequeue_start return value.
+ *
+ * @param r
+ *   A pointer to the ring structure.
+ * @param n
+ *   The number of objects to remove from the ring.
+ */
+__rte_experimental
+static __rte_always_inline void
+rte_ring_dequeue_sg_finish(struct rte_ring *r, unsigned int n)
+{
+	rte_ring_dequeue_elem_finish(r, n);
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _RTE_RING_PEEK_SG_H_ */
-- 
2.17.1