Re: [dpdk-dev] [PATCH v5 1/4] lib/rcu: add resource reclamation APIs

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> Add resource reclamation APIs to make it simple for applications
> and libraries to integrate rte_rcu library.
> 
> Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Reviewed-by: Ola Liljedhal <ola.liljedhal@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
> ---
>  lib/librte_rcu/Makefile            |   2 +-
>  lib/librte_rcu/meson.build         |   7 +
>  lib/librte_rcu/rcu_qsbr_pvt.h      |  66 +++++++++
>  lib/librte_rcu/rte_rcu_qsbr.c      | 227 ++++++++++++++++++++++++++++-
>  lib/librte_rcu/rte_rcu_qsbr.h      | 194 +++++++++++++++++++++++-
>  lib/librte_rcu/rte_rcu_version.map |   4 +
>  lib/meson.build                    |   6 +-
>  7 files changed, 501 insertions(+), 5 deletions(-)
>  create mode 100644 lib/librte_rcu/rcu_qsbr_pvt.h
> 
> diff --git a/lib/librte_rcu/Makefile b/lib/librte_rcu/Makefile
> index 728669975..553bca2ef 100644
> --- a/lib/librte_rcu/Makefile
> +++ b/lib/librte_rcu/Makefile
> @@ -7,7 +7,7 @@ include $(RTE_SDK)/mk/rte.vars.mk
>  LIB = librte_rcu.a
> 
>  CFLAGS += $(WERROR_FLAGS) -I$(SRCDIR) -O3
> -LDLIBS += -lrte_eal
> +LDLIBS += -lrte_eal -lrte_ring
> 
>  EXPORT_MAP := rte_rcu_version.map
> 
> diff --git a/lib/librte_rcu/meson.build b/lib/librte_rcu/meson.build
> index c009ae4b7..3eb2ace17 100644
> --- a/lib/librte_rcu/meson.build
> +++ b/lib/librte_rcu/meson.build
> @@ -3,3 +3,10 @@
> 
>  sources = files('rte_rcu_qsbr.c')
>  headers = files('rte_rcu_qsbr.h')
> +
> +# for clang 32-bit compiles we need libatomic for 64-bit atomic ops
> +if cc.get_id() == 'clang' and dpdk_conf.get('RTE_ARCH_64') == false
> +	ext_deps += cc.find_library('atomic')
> +endif
> +

As a nit - as Pavan patch is already integrated into mainline,
this is not necessary any more, I think.

Also noticed that most of make builds failed due to dependency problem:
http://mails.dpdk.org/archives/test-report/2020-April/127765.html
I can't reproduce it locally, but my guess that we need to move rcu above
ring in this mk file: mk/rte.app.mk
Probably something like that:
diff --git a/mk/rte.app.mk b/mk/rte.app.mk
index da12b9eec..8e5d023de 100644
--- a/mk/rte.app.mk
+++ b/mk/rte.app.mk
@@ -91,13 +91,13 @@ _LDLIBS-$(CONFIG_RTE_LIBRTE_MEMPOOL)        += -lrte_mempool
 _LDLIBS-$(CONFIG_RTE_LIBRTE_STACK)          += -lrte_stack
 _LDLIBS-$(CONFIG_RTE_DRIVER_MEMPOOL_RING)   += -lrte_mempool_ring
 _LDLIBS-$(CONFIG_RTE_LIBRTE_OCTEONTX2_MEMPOOL) += -lrte_mempool_octeontx2
+_LDLIBS-$(CONFIG_RTE_LIBRTE_RCU)            += -lrte_rcu
 _LDLIBS-$(CONFIG_RTE_LIBRTE_RING)           += -lrte_ring
 _LDLIBS-$(CONFIG_RTE_LIBRTE_PCI)            += -lrte_pci
 _LDLIBS-$(CONFIG_RTE_LIBRTE_EAL)            += -lrte_eal
 _LDLIBS-$(CONFIG_RTE_LIBRTE_CMDLINE)        += -lrte_cmdline
 _LDLIBS-$(CONFIG_RTE_LIBRTE_REORDER)        += -lrte_reorder
 _LDLIBS-$(CONFIG_RTE_LIBRTE_SCHED)          += -lrte_sched
-_LDLIBS-$(CONFIG_RTE_LIBRTE_RCU)            += -lrte_rcu

Apart from that - LGTM
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

> +deps += ['ring']
> diff --git a/lib/librte_rcu/rcu_qsbr_pvt.h b/lib/librte_rcu/rcu_qsbr_pvt.h
> new file mode 100644
> index 000000000..63f7a5fff
> --- /dev/null
> +++ b/lib/librte_rcu/rcu_qsbr_pvt.h
> @@ -0,0 +1,66 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright (c) 2020 Arm Limited
> + */
> +
> +#ifndef _RTE_RCU_QSBR_PVT_H_
> +#define _RTE_RCU_QSBR_PVT_H_
> +
> +/**
> + * This file is private to the RCU library. It should not be included
> + * by the user of this library.
> + */
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +
> +#include <rte_ring.h>
> +#include <rte_ring_elem.h>
> +
> +#include "rte_rcu_qsbr.h"
> +
> +/* Defer queue structure.
> + * This structure holds the defer queue. The defer queue is used to
> + * hold the deleted entries from the data structure that are not
> + * yet freed.
> + */
> +struct rte_rcu_qsbr_dq {
> +	struct rte_rcu_qsbr *v; /**< RCU QSBR variable used by this queue.*/
> +	struct rte_ring *r;     /**< RCU QSBR defer queue. */
> +	uint32_t size;
> +	/**< Number of elements in the defer queue */
> +	uint32_t esize;
> +	/**< Size (in bytes) of data, including the token, stored on the
> +	 *   defer queue.
> +	 */
> +	uint32_t trigger_reclaim_limit;
> +	/**< Trigger automatic reclamation after the defer queue
> +	 *   has atleast these many resources waiting.
> +	 */
> +	uint32_t max_reclaim_size;
> +	/**< Reclaim at the max these many resources during auto
> +	 *   reclamation.
> +	 */
> +	rte_rcu_qsbr_free_resource_t free_fn;
> +	/**< Function to call to free the resource. */
> +	void *p;
> +	/**< Pointer passed to the free function. Typically, this is the
> +	 *   pointer to the data structure to which the resource to free
> +	 *   belongs.
> +	 */
> +};
> +
> +/* Internal structure to represent the element on the defer queue.
> + * Use alias as a character array is type casted to a variable
> + * of this structure type.
> + */
> +typedef struct {
> +	uint64_t token;  /**< Token */
> +	uint8_t elem[0]; /**< Pointer to user element */
> +} __attribute__((__may_alias__)) __rte_rcu_qsbr_dq_elem_t;
> +
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif /* _RTE_RCU_QSBR_PVT_H_ */
> diff --git a/lib/librte_rcu/rte_rcu_qsbr.c b/lib/librte_rcu/rte_rcu_qsbr.c
> index 2f3fad776..6a429d8b3 100644
> --- a/lib/librte_rcu/rte_rcu_qsbr.c
> +++ b/lib/librte_rcu/rte_rcu_qsbr.c
> @@ -1,6 +1,6 @@
>  /* SPDX-License-Identifier: BSD-3-Clause
>   *
> - * Copyright (c) 2018 Arm Limited
> + * Copyright (c) 2018-2020 Arm Limited
>   */
> 
>  #include <stdio.h>
> @@ -18,8 +18,10 @@
>  #include <rte_per_lcore.h>
>  #include <rte_lcore.h>
>  #include <rte_errno.h>
> +#include <rte_ring_elem.h>
> 
>  #include "rte_rcu_qsbr.h"
> +#include "rcu_qsbr_pvt.h"
> 
>  /* Get the memory size of QSBR variable */
>  size_t
> @@ -270,6 +272,229 @@ rte_rcu_qsbr_dump(FILE *f, struct rte_rcu_qsbr *v)
>  	return 0;
>  }
> 
> +/* Create a queue used to store the data structure elements that can
> + * be freed later. This queue is referred to as 'defer queue'.
> + */
> +struct rte_rcu_qsbr_dq *
> +rte_rcu_qsbr_dq_create(const struct rte_rcu_qsbr_dq_parameters *params)
> +{
> +	struct rte_rcu_qsbr_dq *dq;
> +	uint32_t qs_fifo_size;
> +	unsigned int flags;
> +
> +	if (params == NULL || params->free_fn == NULL ||
> +		params->v == NULL || params->name == NULL ||
> +		params->size == 0 || params->esize == 0 ||
> +		(params->esize % 4 != 0)) {
> +		rte_log(RTE_LOG_ERR, rte_rcu_log_type,
> +			"%s(): Invalid input parameter\n", __func__);
> +		rte_errno = EINVAL;
> +
> +		return NULL;
> +	}
> +	/* If auto reclamation is configured, reclaim limit
> +	 * should be a valid value.
> +	 */
> +	if ((params->trigger_reclaim_limit <= params->size) &&
> +	    (params->max_reclaim_size == 0)) {
> +		rte_log(RTE_LOG_ERR, rte_rcu_log_type,
> +			"%s(): Invalid input parameter, size = %u, trigger_reclaim_limit = %u, max_reclaim_size = %u\n",
> +			__func__, params->size, params->trigger_reclaim_limit,
> +			params->max_reclaim_size);
> +		rte_errno = EINVAL;
> +
> +		return NULL;
> +	}
> +
> +	dq = rte_zmalloc(NULL, sizeof(struct rte_rcu_qsbr_dq),
> +			 RTE_CACHE_LINE_SIZE);
> +	if (dq == NULL) {
> +		rte_errno = ENOMEM;
> +
> +		return NULL;
> +	}
> +
> +	/* Decide the flags for the ring.
> +	 * If MT safety is requested, use RTS for ring enqueue as most
> +	 * use cases involve dq-enqueue happening on the control plane.
> +	 * Ring dequeue is always HTS due to the possibility of revert.
> +	 */
> +	flags = RING_F_MP_RTS_ENQ;
> +	if (params->flags & RTE_RCU_QSBR_DQ_MT_UNSAFE)
> +		flags = RING_F_SP_ENQ;
> +	flags |= RING_F_MC_HTS_DEQ;
> +	/* round up qs_fifo_size to next power of two that is not less than
> +	 * max_size.
> +	 */
> +	qs_fifo_size = rte_align32pow2(params->size + 1);
> +	/* Add token size to ring element size */
> +	dq->r = rte_ring_create_elem(params->name,
> +			__RTE_QSBR_TOKEN_SIZE + params->esize,
> +			qs_fifo_size, SOCKET_ID_ANY, flags);
> +	if (dq->r == NULL) {
> +		rte_log(RTE_LOG_ERR, rte_rcu_log_type,
> +			"%s(): defer queue create failed\n", __func__);
> +		rte_free(dq);
> +		return NULL;
> +	}
> +
> +	dq->v = params->v;
> +	dq->size = params->size;
> +	dq->esize = __RTE_QSBR_TOKEN_SIZE + params->esize;
> +	dq->trigger_reclaim_limit = params->trigger_reclaim_limit;
> +	dq->max_reclaim_size = params->max_reclaim_size;
> +	dq->free_fn = params->free_fn;
> +	dq->p = params->p;
> +
> +	return dq;
> +}
> +
> +/* Enqueue one resource to the defer queue to free after the grace
> + * period is over.
> + */
> +int rte_rcu_qsbr_dq_enqueue(struct rte_rcu_qsbr_dq *dq, void *e)
> +{
> +	__rte_rcu_qsbr_dq_elem_t *dq_elem;
> +	uint32_t cur_size;
> +
> +	if (dq == NULL || e == NULL) {
> +		rte_log(RTE_LOG_ERR, rte_rcu_log_type,
> +			"%s(): Invalid input parameter\n", __func__);
> +		rte_errno = EINVAL;
> +
> +		return 1;
> +	}
> +
> +	char data[dq->esize];
> +	dq_elem = (__rte_rcu_qsbr_dq_elem_t *)data;
> +	/* Start the grace period */
> +	dq_elem->token = rte_rcu_qsbr_start(dq->v);
> +
> +	/* Reclaim resources if the queue size has hit the reclaim
> +	 * limit. This helps the queue from growing too large and
> +	 * allows time for reader threads to report their quiescent state.
> +	 */
> +	cur_size = rte_ring_count(dq->r);
> +	if (cur_size > dq->trigger_reclaim_limit) {
> +		rte_log(RTE_LOG_INFO, rte_rcu_log_type,
> +			"%s(): Triggering reclamation\n", __func__);
> +		rte_rcu_qsbr_dq_reclaim(dq, dq->max_reclaim_size,
> +						NULL, NULL, NULL);
> +	}
> +
> +	/* Enqueue the token and resource. Generating the token and
> +	 * enqueuing (token + resource) on the queue is not an
> +	 * atomic operation. When the defer queue is shared by multiple
> +	 * writers, this might result in tokens enqueued out of order
> +	 * on the queue. So, some tokens might wait longer than they
> +	 * are required to be reclaimed.
> +	 */
> +	memcpy(dq_elem->elem, e, dq->esize - __RTE_QSBR_TOKEN_SIZE);
> +	/* Check the status as enqueue might fail since the other threads
> +	 * might have used up the freed space.
> +	 * Enqueue uses the configured flags when the DQ was created.
> +	 */
> +	if (rte_ring_enqueue_elem(dq->r, data, dq->esize) != 0) {
> +		rte_log(RTE_LOG_ERR, rte_rcu_log_type,
> +			"%s(): Enqueue failed\n", __func__);
> +		/* Note that the token generated above is not used.
> +		 * Other than wasting tokens, it should not cause any
> +		 * other issues.
> +		 */
> +		rte_log(RTE_LOG_INFO, rte_rcu_log_type,
> +			"%s(): Skipped enqueuing token = %"PRIu64"\n",
> +			__func__, dq_elem->token);
> +
> +		rte_errno = ENOSPC;
> +		return 1;
> +	}
> +
> +	rte_log(RTE_LOG_INFO, rte_rcu_log_type,
> +		"%s(): Enqueued token = %"PRIu64"\n", __func__, dq_elem->token);
> +
> +	return 0;
> +}
> +
> +/* Reclaim resources from the defer queue. */
> +int
> +rte_rcu_qsbr_dq_reclaim(struct rte_rcu_qsbr_dq *dq, unsigned int n,
> +			unsigned int *freed, unsigned int *pending,
> +			unsigned int *available)
> +{
> +	uint32_t cnt;
> +	__rte_rcu_qsbr_dq_elem_t *dq_elem;
> +
> +	if (dq == NULL || n == 0) {
> +		rte_log(RTE_LOG_ERR, rte_rcu_log_type,
> +			"%s(): Invalid input parameter\n", __func__);
> +		rte_errno = EINVAL;
> +
> +		return 1;
> +	}
> +
> +	cnt = 0;
> +
> +	char data[dq->esize];
> +	/* Check reader threads quiescent state and reclaim resources */
> +	while (cnt < n &&
> +		rte_ring_dequeue_bulk_elem_start(dq->r, &data,
> +					dq->esize, 1, available) != 0) {
> +		dq_elem = (__rte_rcu_qsbr_dq_elem_t *)data;
> +
> +		/* Reclaim the resource */
> +		if (rte_rcu_qsbr_check(dq->v, dq_elem->token, false) != 1) {
> +			rte_ring_dequeue_elem_finish(dq->r, 0);
> +			break;
> +		}
> +		rte_ring_dequeue_elem_finish(dq->r, 1);
> +
> +		rte_log(RTE_LOG_INFO, rte_rcu_log_type,
> +			"%s(): Reclaimed token = %"PRIu64"\n",
> +			__func__, dq_elem->token);
> +
> +		dq->free_fn(dq->p, dq_elem->elem, 1);
> +
> +		cnt++;
> +	}
> +
> +	rte_log(RTE_LOG_INFO, rte_rcu_log_type,
> +		"%s(): Reclaimed %u resources\n", __func__, cnt);
> +
> +	if (freed != NULL)
> +		*freed = cnt;
> +	if (pending != NULL)
> +		*pending = rte_ring_count(dq->r);
> +
> +	return 0;
> +}
> +
> +/* Delete a defer queue. */
> +int
> +rte_rcu_qsbr_dq_delete(struct rte_rcu_qsbr_dq *dq)
> +{
> +	unsigned int pending;
> +
> +	if (dq == NULL) {
> +		rte_log(RTE_LOG_DEBUG, rte_rcu_log_type,
> +			"%s(): Invalid input parameter\n", __func__);
> +
> +		return 0;
> +	}
> +
> +	/* Reclaim all the resources */
> +	rte_rcu_qsbr_dq_reclaim(dq, ~0, NULL, &pending, NULL);
> +	if (pending != 0) {
> +		rte_errno = EAGAIN;
> +
> +		return 1;
> +	}
> +
> +	rte_ring_free(dq->r);
> +	rte_free(dq);
> +
> +	return 0;
> +}
> +
>  int rte_rcu_log_type;
> 
>  RTE_INIT(rte_rcu_register)
> diff --git a/lib/librte_rcu/rte_rcu_qsbr.h b/lib/librte_rcu/rte_rcu_qsbr.h
> index 0b5585925..e2fc7f83e 100644
> --- a/lib/librte_rcu/rte_rcu_qsbr.h
> +++ b/lib/librte_rcu/rte_rcu_qsbr.h
> @@ -1,5 +1,5 @@
>  /* SPDX-License-Identifier: BSD-3-Clause
> - * Copyright (c) 2018 Arm Limited
> + * Copyright (c) 2018-2020 Arm Limited
>   */
> 
>  #ifndef _RTE_RCU_QSBR_H_
> @@ -34,6 +34,7 @@ extern "C" {
>  #include <rte_lcore.h>
>  #include <rte_debug.h>
>  #include <rte_atomic.h>
> +#include <rte_ring.h>
> 
>  extern int rte_rcu_log_type;
> 
> @@ -84,6 +85,7 @@ struct rte_rcu_qsbr_cnt {
>  #define __RTE_QSBR_CNT_THR_OFFLINE 0
>  #define __RTE_QSBR_CNT_INIT 1
>  #define __RTE_QSBR_CNT_MAX ((uint64_t)~0)
> +#define __RTE_QSBR_TOKEN_SIZE sizeof(uint64_t)
> 
>  /* RTE Quiescent State variable structure.
>   * This structure has two elements that vary in size based on the
> @@ -114,6 +116,86 @@ struct rte_rcu_qsbr {
>  	 */
>  } __rte_cache_aligned;
> 
> +/**
> + * Call back function called to free the resources.
> + *
> + * @param p
> + *   Pointer provided while creating the defer queue
> + * @param e
> + *   Pointer to the resource data stored on the defer queue
> + * @param n
> + *   Number of resources to free. Currently, this is set to 1.
> + *
> + * @return
> + *   None
> + */
> +typedef void (*rte_rcu_qsbr_free_resource_t)(void *p, void *e, unsigned int n);
> +
> +#define RTE_RCU_QSBR_DQ_NAMESIZE RTE_RING_NAMESIZE
> +
> +/**
> + * Various flags supported.
> + */
> +/**< Enqueue and reclaim operations are multi-thread safe by default.
> + *   The call back functions registered to free the resources are
> + *   assumed to be multi-thread safe.
> + *   Set this flag is multi-thread safety is not required.
> + */
> +#define RTE_RCU_QSBR_DQ_MT_UNSAFE 1
> +
> +/**
> + * Parameters used when creating the defer queue.
> + */
> +struct rte_rcu_qsbr_dq_parameters {
> +	const char *name;
> +	/**< Name of the queue. */
> +	uint32_t flags;
> +	/**< Flags to control API behaviors */
> +	uint32_t size;
> +	/**< Number of entries in queue. Typically, this will be
> +	 *   the same as the maximum number of entries supported in the
> +	 *   lock free data structure.
> +	 *   Data structures with unbounded number of entries is not
> +	 *   supported currently.
> +	 */
> +	uint32_t esize;
> +	/**< Size (in bytes) of each element in the defer queue.
> +	 *   This has to be multiple of 4B.
> +	 */
> +	uint32_t trigger_reclaim_limit;
> +	/**< Trigger automatic reclamation after the defer queue
> +	 *   has atleast these many resources waiting. This auto
> +	 *   reclamation is triggered in rte_rcu_qsbr_dq_enqueue API
> +	 *   call.
> +	 *   If this is greater than 'size', auto reclamation is
> +	 *   not triggered.
> +	 *   If this is set to 0, auto reclamation is triggered
> +	 *   in every call to rte_rcu_qsbr_dq_enqueue API.
> +	 */
> +	uint32_t max_reclaim_size;
> +	/**< When automatic reclamation is enabled, reclaim at the max
> +	 *   these many resources. This should contain a valid value, if
> +	 *   auto reclamation is on. Setting this to 'size' or greater will
> +	 *   reclaim all possible resources currently on the defer queue.
> +	 */
> +	rte_rcu_qsbr_free_resource_t free_fn;
> +	/**< Function to call to free the resource. */
> +	void *p;
> +	/**< Pointer passed to the free function. Typically, this is the
> +	 *   pointer to the data structure to which the resource to free
> +	 *   belongs. This can be NULL.
> +	 */
> +	struct rte_rcu_qsbr *v;
> +	/**< RCU QSBR variable to use for this defer queue */
> +};
> +
> +/* RTE defer queue structure.
> + * This structure holds the defer queue. The defer queue is used to
> + * hold the deleted entries from the data structure that are not
> + * yet freed.
> + */
> +struct rte_rcu_qsbr_dq;
> +
>  /**
>   * @warning
>   * @b EXPERIMENTAL: this API may change without prior notice
> @@ -692,6 +774,116 @@ __rte_experimental
>  int
>  rte_rcu_qsbr_dump(FILE *f, struct rte_rcu_qsbr *v);
> 
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice
> + *
> + * Create a queue used to store the data structure elements that can
> + * be freed later. This queue is referred to as 'defer queue'.
> + *
> + * @param params
> + *   Parameters to create a defer queue.
> + * @return
> + *   On success - Valid pointer to defer queue
> + *   On error - NULL
> + *   Possible rte_errno codes are:
> + *   - EINVAL - NULL parameters are passed
> + *   - ENOMEM - Not enough memory
> + */
> +__rte_experimental
> +struct rte_rcu_qsbr_dq *
> +rte_rcu_qsbr_dq_create(const struct rte_rcu_qsbr_dq_parameters *params);
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice
> + *
> + * Enqueue one resource to the defer queue and start the grace period.
> + * The resource will be freed later after at least one grace period
> + * is over.
> + *
> + * If the defer queue is full, it will attempt to reclaim resources.
> + * It will also reclaim resources at regular intervals to avoid
> + * the defer queue from growing too big.
> + *
> + * Multi-thread safety is provided as the defer queue configuration.
> + * When multi-thread safety is requested, it is possible that the
> + * resources are not stored in their order of deletion. This results
> + * in resources being held in the defer queue longer than they should.
> + *
> + * @param dq
> + *   Defer queue to allocate an entry from.
> + * @param e
> + *   Pointer to resource data to copy to the defer queue. The size of
> + *   the data to copy is equal to the element size provided when the
> + *   defer queue was created.
> + * @return
> + *   On success - 0
> + *   On error - 1 with rte_errno set to
> + *   - EINVAL - NULL parameters are passed
> + *   - ENOSPC - Defer queue is full. This condition can not happen
> + *		if the defer queue size is equal (or larger) than the
> + *		number of elements in the data structure.
> + */
> +__rte_experimental
> +int
> +rte_rcu_qsbr_dq_enqueue(struct rte_rcu_qsbr_dq *dq, void *e);
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice
> + *
> + * Free quesed resources from the defer queue.
> + *
> + * This API is multi-thread safe.
> + *
> + * @param dq
> + *   Defer queue to free an entry from.
> + * @param n
> + *   Maximum number of resources to free.
> + * @param freed
> + *   Number of resources that were freed.
> + * @param pending
> + *   Number of resources pending on the defer queue. This number might not
> + *   be acurate if multi-thread safety is configured.
> + * @param available
> + *   Number of resources that can be added to the defer queue.
> + *   This number might not be acurate if multi-thread safety is configured.
> + * @return
> + *   On successful reclamation of at least 1 resource - 0
> + *   On error - 1 with rte_errno set to
> + *   - EINVAL - NULL parameters are passed
> + */
> +__rte_experimental
> +int
> +rte_rcu_qsbr_dq_reclaim(struct rte_rcu_qsbr_dq *dq, unsigned int n,
> +	unsigned int *freed, unsigned int *pending, unsigned int *available);
> +
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice
> + *
> + * Delete a defer queue.
> + *
> + * It tries to reclaim all the resources on the defer queue.
> + * If any of the resources have not completed the grace period
> + * the reclamation stops and returns immediately. The rest of
> + * the resources are not reclaimed and the defer queue is not
> + * freed.
> + *
> + * @param dq
> + *   Defer queue to delete.
> + * @return
> + *   On success - 0
> + *   On error - 1
> + *   Possible rte_errno codes are:
> + *   - EAGAIN - Some of the resources have not completed at least 1 grace
> + *		period, try again.
> + */
> +__rte_experimental
> +int
> +rte_rcu_qsbr_dq_delete(struct rte_rcu_qsbr_dq *dq);
> +
>  #ifdef __cplusplus
>  }
>  #endif
> diff --git a/lib/librte_rcu/rte_rcu_version.map b/lib/librte_rcu/rte_rcu_version.map
> index f8b9ef2ab..dfac88a37 100644
> --- a/lib/librte_rcu/rte_rcu_version.map
> +++ b/lib/librte_rcu/rte_rcu_version.map
> @@ -8,6 +8,10 @@ EXPERIMENTAL {
>  	rte_rcu_qsbr_synchronize;
>  	rte_rcu_qsbr_thread_register;
>  	rte_rcu_qsbr_thread_unregister;
> +	rte_rcu_qsbr_dq_create;
> +	rte_rcu_qsbr_dq_enqueue;
> +	rte_rcu_qsbr_dq_reclaim;
> +	rte_rcu_qsbr_dq_delete;
> 
>  	local: *;
>  };
> diff --git a/lib/meson.build b/lib/meson.build
> index 63c17ee75..c28b8df83 100644
> --- a/lib/meson.build
> +++ b/lib/meson.build
> @@ -11,7 +11,9 @@
>  libraries = [
>  	'kvargs', # eal depends on kvargs
>  	'eal', # everything depends on eal
> -	'ring', 'mempool', 'mbuf', 'net', 'meter', 'ethdev', 'pci', # core
> +	'ring',
> +	'rcu', # rcu depends on ring
> +	'mempool', 'mbuf', 'net', 'meter', 'ethdev', 'pci', # core
>  	'cmdline',
>  	'metrics', # bitrate/latency stats depends on this
>  	'hash',    # efd depends on this
> @@ -22,7 +24,7 @@ libraries = [
>  	'gro', 'gso', 'ip_frag', 'jobstats',
>  	'kni', 'latencystats', 'lpm', 'member',
>  	'power', 'pdump', 'rawdev',
> -	'rcu', 'rib', 'reorder', 'sched', 'security', 'stack', 'vhost',
> +	'rib', 'reorder', 'sched', 'security', 'stack', 'vhost',
>  	# ipsec lib depends on net, crypto and security
>  	'ipsec',
>  	#fib lib depends on rib
> --
> 2.17.1