Re: [dpdk-dev] [PATCH v3 2/3] lib/rcu: add resource reclamation APIs

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>

> 
> Hi Honnappa,
> 
> On 13/10/2019 04:02, Honnappa Nagarahalli wrote:
> > Hi Vladimir,
> > 	Apologies for the delayed response, I had to run few experiments.
> >
> > <snip>
> >
> >> Hi Honnappa,
> >>
> >> On 01/10/2019 07:29, Honnappa Nagarahalli wrote:
> >>> 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>
> >>> ---
> >>>    app/test/test_rcu_qsbr.c           | 291 ++++++++++++++++++++++++++++-
> >>>    lib/librte_rcu/meson.build         |   2 +
> >>>    lib/librte_rcu/rte_rcu_qsbr.c      | 185 ++++++++++++++++++
> >>>    lib/librte_rcu/rte_rcu_qsbr.h      | 169 +++++++++++++++++
> >>>    lib/librte_rcu/rte_rcu_qsbr_pvt.h  |  46 +++++
> >>>    lib/librte_rcu/rte_rcu_version.map |   4 +
> >>>    lib/meson.build                    |   6 +-
> >>>    7 files changed, 700 insertions(+), 3 deletions(-)
> >>>    create mode 100644 lib/librte_rcu/rte_rcu_qsbr_pvt.h
> >>>
> >>> diff --git a/app/test/test_rcu_qsbr.c b/app/test/test_rcu_qsbr.c
> >>> index
> >>> d1b9e46a2..3a6815243 100644
> >>> --- a/app/test/test_rcu_qsbr.c
> >>> +++ b/app/test/test_rcu_qsbr.c
> >>> @@ -1,8 +1,9 @@
> >>>    /* SPDX-License-Identifier: BSD-3-Clause
> >>> - * Copyright (c) 2018 Arm Limited
> >>> + * Copyright (c) 2019 Arm Limited
> >>>     */
> >>>
> >>>    #include <stdio.h>
> >>> +#include <string.h>
> >>>    #include <rte_pause.h>
> >>>    #include <rte_rcu_qsbr.h>
> >>>    #include <rte_hash.h>
> >>> @@ -33,6 +34,7 @@ static uint32_t *keys;
> >>>    #define COUNTER_VALUE 4096
> >>>    static uint32_t *hash_data[RTE_MAX_LCORE][TOTAL_ENTRY];
> >>>    static uint8_t writer_done;
> >>> +static uint8_t cb_failed;
> >>>
> >>>    static struct rte_rcu_qsbr *t[RTE_MAX_LCORE];
> >>>    struct rte_hash *h[RTE_MAX_LCORE]; @@ -582,6 +584,269 @@
> >>> test_rcu_qsbr_thread_offline(void)
> >>>    	return 0;
> >>>    }
> >>>
> >>> +static void
> >>> +rte_rcu_qsbr_test_free_resource(void *p, void *e) {
> >>> +	if (p != NULL && e != NULL) {
> >>> +		printf("%s: Test failed\n", __func__);
> >>> +		cb_failed = 1;
> >>> +	}
> >>> +}
> >>> +
> >>> +/*
> >>> + * rte_rcu_qsbr_dq_create: create a queue used to store the data
> >>> +structure
> >>> + * elements that can be freed later. This queue is referred to as
> >>> +'defer
> >> queue'.
> >>> + */
> >>> +static int
> >>> +test_rcu_qsbr_dq_create(void)
> >>> +{
> >>> +	char rcu_dq_name[RTE_RING_NAMESIZE];
> >>> +	struct rte_rcu_qsbr_dq_parameters params;
> >>> +	struct rte_rcu_qsbr_dq *dq;
> >>> +
> >>> +	printf("\nTest rte_rcu_qsbr_dq_create()\n");
> >>> +
> >>> +	/* Pass invalid parameters */
> >>> +	dq = rte_rcu_qsbr_dq_create(NULL);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq != NULL), "dq create invalid
> >>> +params");
> >>> +
> >>> +	memset(&params, 0, sizeof(struct rte_rcu_qsbr_dq_parameters));
> >>> +	dq = rte_rcu_qsbr_dq_create(&params);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq != NULL), "dq create invalid
> >>> +params");
> >>> +
> >>> +	snprintf(rcu_dq_name, sizeof(rcu_dq_name), "TEST_RCU");
> >>> +	params.name = rcu_dq_name;
> >>> +	dq = rte_rcu_qsbr_dq_create(&params);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq != NULL), "dq create invalid
> >>> +params");
> >>> +
> >>> +	params.f = rte_rcu_qsbr_test_free_resource;
> >>> +	dq = rte_rcu_qsbr_dq_create(&params);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq != NULL), "dq create invalid
> >>> +params");
> >>> +
> >>> +	rte_rcu_qsbr_init(t[0], RTE_MAX_LCORE);
> >>> +	params.v = t[0];
> >>> +	dq = rte_rcu_qsbr_dq_create(&params);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq != NULL), "dq create invalid
> >>> +params");
> >>> +
> >>> +	params.size = 1;
> >>> +	dq = rte_rcu_qsbr_dq_create(&params);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq != NULL), "dq create invalid
> >>> +params");
> >>> +
> >>> +	params.esize = 3;
> >>> +	dq = rte_rcu_qsbr_dq_create(&params);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq != NULL), "dq create invalid
> >>> +params");
> >>> +
> >>> +	/* Pass all valid parameters */
> >>> +	params.esize = 16;
> >>> +	dq = rte_rcu_qsbr_dq_create(&params);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq == NULL), "dq create valid
> >> params");
> >>> +	rte_rcu_qsbr_dq_delete(dq);
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +
> >>> +/*
> >>> + * rte_rcu_qsbr_dq_enqueue: enqueue one resource to the defer
> >>> +queue,
> >>> + * to be freed later after atleast one grace period is over.
> >>> + */
> >>> +static int
> >>> +test_rcu_qsbr_dq_enqueue(void)
> >>> +{
> >>> +	int ret;
> >>> +	uint64_t r;
> >>> +	char rcu_dq_name[RTE_RING_NAMESIZE];
> >>> +	struct rte_rcu_qsbr_dq_parameters params;
> >>> +	struct rte_rcu_qsbr_dq *dq;
> >>> +
> >>> +	printf("\nTest rte_rcu_qsbr_dq_enqueue()\n");
> >>> +
> >>> +	/* Create a queue with simple parameters */
> >>> +	memset(&params, 0, sizeof(struct rte_rcu_qsbr_dq_parameters));
> >>> +	snprintf(rcu_dq_name, sizeof(rcu_dq_name), "TEST_RCU");
> >>> +	params.name = rcu_dq_name;
> >>> +	params.f = rte_rcu_qsbr_test_free_resource;
> >>> +	rte_rcu_qsbr_init(t[0], RTE_MAX_LCORE);
> >>> +	params.v = t[0];
> >>> +	params.size = 1;
> >>> +	params.esize = 16;
> >>> +	dq = rte_rcu_qsbr_dq_create(&params);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq == NULL), "dq create valid
> >>> +params");
> >>> +
> >>> +	/* Pass invalid parameters */
> >>> +	ret = rte_rcu_qsbr_dq_enqueue(NULL, NULL);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret == 0), "dq enqueue invalid
> >>> +params");
> >>> +
> >>> +	ret = rte_rcu_qsbr_dq_enqueue(dq, NULL);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret == 0), "dq enqueue invalid
> >>> +params");
> >>> +
> >>> +	ret = rte_rcu_qsbr_dq_enqueue(NULL, &r);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret == 0), "dq enqueue invalid
> >>> +params");
> >>> +
> >>> +	ret = rte_rcu_qsbr_dq_delete(dq);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret == 1), "dq delete valid
> >> params");
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +
> >>> +/*
> >>> + * rte_rcu_qsbr_dq_reclaim: Reclaim resources from the defer queue.
> >>> + */
> >>> +static int
> >>> +test_rcu_qsbr_dq_reclaim(void)
> >>> +{
> >>> +	int ret;
> >>> +
> >>> +	printf("\nTest rte_rcu_qsbr_dq_reclaim()\n");
> >>> +
> >>> +	/* Pass invalid parameters */
> >>> +	ret = rte_rcu_qsbr_dq_reclaim(NULL);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret != 1), "dq reclaim invalid
> >>> +params");
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +
> >>> +/*
> >>> + * rte_rcu_qsbr_dq_delete: Delete a defer queue.
> >>> + */
> >>> +static int
> >>> +test_rcu_qsbr_dq_delete(void)
> >>> +{
> >>> +	int ret;
> >>> +	char rcu_dq_name[RTE_RING_NAMESIZE];
> >>> +	struct rte_rcu_qsbr_dq_parameters params;
> >>> +	struct rte_rcu_qsbr_dq *dq;
> >>> +
> >>> +	printf("\nTest rte_rcu_qsbr_dq_delete()\n");
> >>> +
> >>> +	/* Pass invalid parameters */
> >>> +	ret = rte_rcu_qsbr_dq_delete(NULL);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret != 1), "dq delete invalid
> >>> +params");
> >>> +
> >>> +	memset(&params, 0, sizeof(struct rte_rcu_qsbr_dq_parameters));
> >>> +	snprintf(rcu_dq_name, sizeof(rcu_dq_name), "TEST_RCU");
> >>> +	params.name = rcu_dq_name;
> >>> +	params.f = rte_rcu_qsbr_test_free_resource;
> >>> +	rte_rcu_qsbr_init(t[0], RTE_MAX_LCORE);
> >>> +	params.v = t[0];
> >>> +	params.size = 1;
> >>> +	params.esize = 16;
> >>> +	dq = rte_rcu_qsbr_dq_create(&params);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq == NULL), "dq create valid
> >> params");
> >>> +	ret = rte_rcu_qsbr_dq_delete(dq);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret != 0), "dq delete valid
> >> params");
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +
> >>> +/*
> >>> + * rte_rcu_qsbr_dq_enqueue: enqueue one resource to the defer
> >>> +queue,
> >>> + * to be freed later after atleast one grace period is over.
> >>> + */
> >>> +static int
> >>> +test_rcu_qsbr_dq_functional(int32_t size, int32_t esize) {
> >>> +	int i, j, ret;
> >>> +	char rcu_dq_name[RTE_RING_NAMESIZE];
> >>> +	struct rte_rcu_qsbr_dq_parameters params;
> >>> +	struct rte_rcu_qsbr_dq *dq;
> >>> +	uint64_t *e;
> >>> +	uint64_t sc = 200;
> >>> +	int max_entries;
> >>> +
> >>> +	printf("\nTest rte_rcu_qsbr_dq_xxx functional tests()\n");
> >>> +	printf("Size = %d, esize = %d\n", size, esize);
> >>> +
> >>> +	e = (uint64_t *)rte_zmalloc(NULL, esize, RTE_CACHE_LINE_SIZE);
> >>> +	if (e == NULL)
> >>> +		return 0;
> >>> +	cb_failed = 0;
> >>> +
> >>> +	/* Initialize the RCU variable. No threads are registered */
> >>> +	rte_rcu_qsbr_init(t[0], RTE_MAX_LCORE);
> >>> +
> >>> +	/* Create a queue with simple parameters */
> >>> +	memset(&params, 0, sizeof(struct rte_rcu_qsbr_dq_parameters));
> >>> +	snprintf(rcu_dq_name, sizeof(rcu_dq_name), "TEST_RCU");
> >>> +	params.name = rcu_dq_name;
> >>> +	params.f = rte_rcu_qsbr_test_free_resource;
> >>> +	params.v = t[0];
> >>> +	params.size = size;
> >>> +	params.esize = esize;
> >>> +	dq = rte_rcu_qsbr_dq_create(&params);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((dq == NULL), "dq create valid
> >>> +params");
> >>> +
> >>> +	/* Given the size and esize, calculate the maximum number of entries
> >>> +	 * that can be stored on the defer queue (look at the logic used
> >>> +	 * in capacity calculation of rte_ring).
> >>> +	 */
> >>> +	max_entries = rte_align32pow2(((esize/8 + 1) * size) + 1);
> >>> +	max_entries = (max_entries - 1)/(esize/8 + 1);
> >>> +
> >>> +	/* Enqueue few counters starting with the value 'sc' */
> >>> +	/* The queue size will be rounded up to 2. The enqueue API also
> >>> +	 * reclaims if the queue size is above certain limit. Since, there
> >>> +	 * are no threads registered, reclamation succedes. Hence, it should
> >>> +	 * be possible to enqueue more than the provided queue size.
> >>> +	 */
> >>> +	for (i = 0; i < 10; i++) {
> >>> +		ret = rte_rcu_qsbr_dq_enqueue(dq, e);
> >>> +		TEST_RCU_QSBR_RETURN_IF_ERROR((ret != 0),
> >>> +			"dq enqueue functional");
> >>> +		for (j = 0; j < esize/8; j++)
> >>> +			e[j] = sc++;
> >>> +	}
> >>> +
> >>> +	/* Register a thread on the RCU QSBR variable. Reclamation will not
> >>> +	 * succeed. It should not be possible to enqueue more than the size
> >>> +	 * number of resources.
> >>> +	 */
> >>> +	rte_rcu_qsbr_thread_register(t[0], 1);
> >>> +	rte_rcu_qsbr_thread_online(t[0], 1);
> >>> +
> >>> +	for (i = 0; i < max_entries; i++) {
> >>> +		ret = rte_rcu_qsbr_dq_enqueue(dq, e);
> >>> +		TEST_RCU_QSBR_RETURN_IF_ERROR((ret != 0),
> >>> +			"dq enqueue functional");
> >>> +		for (j = 0; j < esize/8; j++)
> >>> +			e[j] = sc++;
> >>> +	}
> >>> +
> >>> +	/* Enqueue fails as queue is full */
> >>> +	ret = rte_rcu_qsbr_dq_enqueue(dq, e);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret == 0), "dq enqueue
> >> functional");
> >>> +
> >>> +	/* Delete should fail as there are elements in defer queue which
> >>> +	 * cannot be reclaimed.
> >>> +	 */
> >>> +	ret = rte_rcu_qsbr_dq_delete(dq);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret == 0), "dq delete valid
> >> params");
> >>> +
> >>> +	/* Report quiescent state, enqueue should succeed */
> >>> +	rte_rcu_qsbr_quiescent(t[0], 1);
> >>> +	for (i = 0; i < max_entries; i++) {
> >>> +		ret = rte_rcu_qsbr_dq_enqueue(dq, e);
> >>> +		TEST_RCU_QSBR_RETURN_IF_ERROR((ret != 0),
> >>> +			"dq enqueue functional");
> >>> +		for (j = 0; j < esize/8; j++)
> >>> +			e[j] = sc++;
> >>> +	}
> >>> +
> >>> +	/* Queue is full */
> >>> +	ret = rte_rcu_qsbr_dq_enqueue(dq, e);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret == 0), "dq enqueue
> >> functional");
> >>> +
> >>> +	/* Report quiescent state, delete should succeed */
> >>> +	rte_rcu_qsbr_quiescent(t[0], 1);
> >>> +	ret = rte_rcu_qsbr_dq_delete(dq);
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((ret != 0), "dq delete valid
> >> params");
> >>> +
> >>> +	/* Validate that call back function did not return any error */
> >>> +	TEST_RCU_QSBR_RETURN_IF_ERROR((cb_failed == 1), "CB failed");
> >>> +
> >>> +	rte_free(e);
> >>> +	return 0;
> >>> +}
> >>> +
> >>>    /*
> >>>     * rte_rcu_qsbr_dump: Dump status of a single QS variable to a file
> >>>     */
> >>> @@ -1025,6 +1290,18 @@ test_rcu_qsbr_main(void)
> >>>    	if (test_rcu_qsbr_thread_offline() < 0)
> >>>    		goto test_fail;
> >>>
> >>> +	if (test_rcu_qsbr_dq_create() < 0)
> >>> +		goto test_fail;
> >>> +
> >>> +	if (test_rcu_qsbr_dq_reclaim() < 0)
> >>> +		goto test_fail;
> >>> +
> >>> +	if (test_rcu_qsbr_dq_delete() < 0)
> >>> +		goto test_fail;
> >>> +
> >>> +	if (test_rcu_qsbr_dq_enqueue() < 0)
> >>> +		goto test_fail;
> >>> +
> >>>    	printf("\nFunctional tests\n");
> >>>
> >>>    	if (test_rcu_qsbr_sw_sv_3qs() < 0) @@ -1033,6 +1310,18 @@
> >>> test_rcu_qsbr_main(void)
> >>>    	if (test_rcu_qsbr_mw_mv_mqs() < 0)
> >>>    		goto test_fail;
> >>>
> >>> +	if (test_rcu_qsbr_dq_functional(1, 8) < 0)
> >>> +		goto test_fail;
> >>> +
> >>> +	if (test_rcu_qsbr_dq_functional(2, 8) < 0)
> >>> +		goto test_fail;
> >>> +
> >>> +	if (test_rcu_qsbr_dq_functional(303, 16) < 0)
> >>> +		goto test_fail;
> >>> +
> >>> +	if (test_rcu_qsbr_dq_functional(7, 128) < 0)
> >>> +		goto test_fail;
> >>> +
> >>>    	free_rcu();
> >>>
> >>>    	printf("\n");
> >>> diff --git a/lib/librte_rcu/meson.build b/lib/librte_rcu/meson.build
> >>> index 62920ba02..e280b29c1 100644
> >>> --- a/lib/librte_rcu/meson.build
> >>> +++ b/lib/librte_rcu/meson.build
> >>> @@ -10,3 +10,5 @@ headers = files('rte_rcu_qsbr.h')
> >>>    if cc.get_id() == 'clang' and dpdk_conf.get('RTE_ARCH_64') == false
> >>>    	ext_deps += cc.find_library('atomic')
> >>>    endif
> >>> +
> >>> +deps += ['ring']
> >>> diff --git a/lib/librte_rcu/rte_rcu_qsbr.c
> >>> b/lib/librte_rcu/rte_rcu_qsbr.c index ce7f93dd3..76814f50b 100644
> >>> --- a/lib/librte_rcu/rte_rcu_qsbr.c
> >>> +++ b/lib/librte_rcu/rte_rcu_qsbr.c
> >>> @@ -21,6 +21,7 @@
> >>>    #include <rte_errno.h>
> >>>
> >>>    #include "rte_rcu_qsbr.h"
> >>> +#include "rte_rcu_qsbr_pvt.h"
> >>>
> >>>    /* Get the memory size of QSBR variable */
> >>>    size_t
> >>> @@ -267,6 +268,190 @@ 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;
> >>> +
> >>> +	if (params == NULL || params->f == NULL ||
> >>> +		params->v == NULL || params->name == NULL ||
> >>> +		params->size == 0 || params->esize == 0 ||
> >>> +		(params->esize % 8 != 0)) {
> >>> +		rte_log(RTE_LOG_ERR, rte_rcu_log_type,
> >>> +			"%s(): Invalid input parameter\n", __func__);
> >>> +		rte_errno = EINVAL;
> >>> +
> >>> +		return NULL;
> >>> +	}
> >>> +
> >>> +	dq = rte_zmalloc(NULL,
> >>> +		(sizeof(struct rte_rcu_qsbr_dq) + params->esize),
> >>> +		RTE_CACHE_LINE_SIZE);
> >>> +	if (dq == NULL) {
> >>> +		rte_errno = ENOMEM;
> >>> +
> >>> +		return NULL;
> >>> +	}
> >>> +
> >>> +	/* round up qs_fifo_size to next power of two that is not less than
> >>> +	 * max_size.
> >>> +	 */
> >>> +	qs_fifo_size = rte_align32pow2((((params->esize/8) + 1)
> >>> +					* params->size) + 1);
> >>> +	dq->r = rte_ring_create(params->name, qs_fifo_size,
> >>> +					SOCKET_ID_ANY, 0);
> >>> +	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 = params->esize;
> >>> +	dq->f = params->f;
> >>> +	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) {
> >>> +	uint64_t token;
> >>> +	uint64_t *tmp;
> >>> +	uint32_t i;
> >>> +	uint32_t cur_size, free_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;
> >>> +	}
> >>> +
> >>> +	/* Start the grace period */
> >>> +	token = rte_rcu_qsbr_start(dq->v);
> >>> +
> >>> +	/* Reclaim resources if the queue is 1/8th full. 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) / (dq->esize/8 + 1);
> >>> +	if (cur_size > (dq->size >> RTE_RCU_QSBR_AUTO_RECLAIM_LIMIT)) {
> >>> +		rte_log(RTE_LOG_INFO, rte_rcu_log_type,
> >>> +			"%s(): Triggering reclamation\n", __func__);
> >>> +		rte_rcu_qsbr_dq_reclaim(dq);
> >>> +	}
> >> There are two problems I see:
> >>
> >> 1. rte_rcu_qsbr_dq_reclaim() reclaims only 1/16 of the defer queue
> >> while it triggers on 1/8. This means that there will always be 1/16
> >> of non reclaimed entries in the queue.
> > There will be 'at least' 1/16 non-reclaimed entries.
> Correct, that's what I meant :)
> >   It could be more depending on the length of the grace period and the rate
> of deletion.
> 
> Right, the number of entries to reclaim depends on:
> 
> - grace period which is application specific
> 
> - cost of delete operation which is library (algorithm) specific
> 
> - rate of deletion which depends on runtime.
> 
> So it is very hard to predict how big should be threshold to trigger
> reclamation and how many entries should it reclaim.
> 
> > The trigger of 1/8 is used to give sufficient time for the readers to report
> their quiescent state. 1/16 is used to spread the load of reclamation across
> multiple calls and provide a upper bound on the cycles consumed.
> 
> 1/16 of max entries to reclaim within single call can cost a lot.
> Moreover, it could have an impact on the readers through massive cache
> evictions.
> 
> Consider a set of routes from test_lpm_perf.c. To install all routes you need
> to have at least 65k tbl8 entries (now it has 2k). So when reclaiming, besides
> the costs of rte_rcu_qsbr_check(), you'll need to rewrite 4k cache lines.
> 
> So 1/16 of max entries is relatively big and it's better to spread this load
> across multiple calls.
> 
> >
> >> 2. Number of entries to reclaim depend on dq->size. So,
> >> rte_rcu_qsbr_dq_reclaim() could take a lot of cycles. For LPM library
> >> this
> > That is true. It depends on dq->size (number of tbl8 groups). However, note
> that there is patch [1] which provides batch reclamation kind of behavior
> which reduces the cycles consumed by reclamation significantly.
> >
> > [1] https://patches.dpdk.org/patch/58960/
> >
> >> means that rte_lpm_delete() sometimes takes a long time.
> > Agree, sometimes takes additional time. It is good to spread it over multiple
> calls.
> Right, with batch reclamation we have here classic throughput vs latency
> problem. Either reclaiming big number of entries relatively infrequently
> spreading the cost of readers quiescent state check or reclaiming small
> amount of entries more often spending more cycles in average. I'd prefer
> latency here because as I mentioned earlier huge batches could have an
> impact on readers and lead to big difference in cost of delete().
> >
> >> So, my suggestions here would be
> >>
> >> - trigger rte_rcu_qsbr_dq_reclaim() with every enqueue
> > Given that the LPM APIs are mainly for control plane, I would think that,
> the next time LPM API is called, the readers have completed the grace period.
> But if there are frequent updates, we might end up with empty reclaims
> which will waste cycles. IMO, this trigger should happen after at least few
> entries are in the queue.
> >
> >> - reclaim small amount of entries (could be configurable of creation
> >> time)
> > Agree. I would keep it a smaller than the trigger amount knowing that the
> elements added right before the trigger might not have completed the grace
> period.
> >
> >> - provide API to trigger reclaim from the application manually.
> > IMO, this will add additional complexity to the application. I agree that
> there will be special needs for some applications. I think those applications
> might have to implement their own methods using the base RCU APIs.
> > Instead, as agreed in other threads, I suggest we expose the parameters
> (when to trigger and how much to reclaim) to the application as optional
> configurable parameters. i.e. if the application does not provide we can use
> default values. I think this should provide enough flexibility to the application.
> 
> Agree.
> 
> Regarding default values, one strategy could be:
> 
> - if reported threshold isn't set (i.e. is equal 0) then call reclaim with every
> enqueue (i.e. threshold == 1)
> 
> - if max_entries_to_reclaim isn't set then reclaim as much as we can
> 
Ok, sounds good.

> 
> >>> +
> >>> +	/* Check if there is space for atleast for 1 resource */
> >>> +	free_size = rte_ring_free_count(dq->r) / (dq->esize/8 + 1);
> >>> +	if (!free_size) {
> >>> +		rte_log(RTE_LOG_ERR, rte_rcu_log_type,
> >>> +			"%s(): Defer queue is full\n", __func__);
> >>> +		rte_errno = ENOSPC;
> >>> +		return 1;
> >>> +	}
> >>> +
> >>> +	/* Enqueue the resource */
> >>> +	rte_ring_sp_enqueue(dq->r, (void *)(uintptr_t)token);
> >>> +
> >>> +	/* The resource to enqueue needs to be a multiple of 64b
> >>> +	 * due to the limitation of the rte_ring implementation.
> >>> +	 */
> >>> +	for (i = 0, tmp = (uint64_t *)e; i < dq->esize/8; i++, tmp++)
> >>> +		rte_ring_sp_enqueue(dq->r, (void *)(uintptr_t)*tmp);
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +
> >>> +/* Reclaim resources from the defer queue. */ int
> >>> +rte_rcu_qsbr_dq_reclaim(struct rte_rcu_qsbr_dq *dq) {
> >>> +	uint32_t max_cnt;
> >>> +	uint32_t cnt;
> >>> +	void *token;
> >>> +	uint64_t *tmp;
> >>> +	uint32_t i;
> >>> +
> >>> +	if (dq == NULL) {
> >>> +		rte_log(RTE_LOG_ERR, rte_rcu_log_type,
> >>> +			"%s(): Invalid input parameter\n", __func__);
> >>> +		rte_errno = EINVAL;
> >>> +
> >>> +		return 1;
> >>> +	}
> >>> +
> >>> +	/* Anything to reclaim? */
> >>> +	if (rte_ring_count(dq->r) == 0)
> >>> +		return 0;
> >>> +
> >>> +	/* Reclaim at the max 1/16th the total number of entries. */
> >>> +	max_cnt = dq->size >> RTE_RCU_QSBR_MAX_RECLAIM_LIMIT;
> >>> +	max_cnt = (max_cnt == 0) ? dq->size : max_cnt;
> >>> +	cnt = 0;
> >>> +
> >>> +	/* Check reader threads quiescent state and reclaim resources */
> >>> +	while ((cnt < max_cnt) && (rte_ring_peek(dq->r, &token) == 0) &&
> >>> +		(rte_rcu_qsbr_check(dq->v, (uint64_t)((uintptr_t)token), false)
> >>> +			== 1)) {
> >>> +		(void)rte_ring_sc_dequeue(dq->r, &token);
> >>> +		/* The resource to dequeue needs to be a multiple of 64b
> >>> +		 * due to the limitation of the rte_ring implementation.
> >>> +		 */
> >>> +		for (i = 0, tmp = (uint64_t *)dq->e; i < dq->esize/8;
> >>> +			i++, tmp++)
> >>> +			(void)rte_ring_sc_dequeue(dq->r,
> >>> +					(void *)(uintptr_t)tmp);
> >>> +		dq->f(dq->p, dq->e);
> >>> +
> >>> +		cnt++;
> >>> +	}
> >>> +
> >>> +	rte_log(RTE_LOG_INFO, rte_rcu_log_type,
> >>> +		"%s(): Reclaimed %u resources\n", __func__, cnt);
> >>> +
> >>> +	if (cnt == 0) {
> >>> +		/* No resources were reclaimed */
> >>> +		rte_errno = EAGAIN;
> >>> +		return 1;
> >>> +	}
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +
> >>> +/* Delete a defer queue. */
> >>> +int
> >>> +rte_rcu_qsbr_dq_delete(struct rte_rcu_qsbr_dq *dq) {
> >>> +	if (dq == NULL) {
> >>> +		rte_log(RTE_LOG_ERR, rte_rcu_log_type,
> >>> +			"%s(): Invalid input parameter\n", __func__);
> >>> +		rte_errno = EINVAL;
> >>> +
> >>> +		return 1;
> >>> +	}
> >>> +
> >>> +	/* Reclaim all the resources */
> >>> +	if (rte_rcu_qsbr_dq_reclaim(dq) != 0)
> >>> +		/* Error number is already set by the reclaim API */
> >>> +		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 c80f15c00..185d4b50a 100644
> >>> --- a/lib/librte_rcu/rte_rcu_qsbr.h
> >>> +++ b/lib/librte_rcu/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;
> >>>
> >>> @@ -109,6 +110,67 @@ 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
> >>> + *
> >>> + * @return
> >>> + *   None
> >>> + */
> >>> +typedef void (*rte_rcu_qsbr_free_resource)(void *p, void *e);
> >>> +
> >>> +#define RTE_RCU_QSBR_DQ_NAMESIZE RTE_RING_NAMESIZE
> >>> +
> >>> +/**
> >>> + *  Trigger automatic reclamation after 1/8th the defer queue is full.
> >>> + */
> >>> +#define RTE_RCU_QSBR_AUTO_RECLAIM_LIMIT 3
> >>> +
> >>> +/**
> >>> + *  Reclaim at the max 1/16th the total number of resources.
> >>> + */
> >>> +#define RTE_RCU_QSBR_MAX_RECLAIM_LIMIT 4
> >>> +
> >>> +/**
> >>> + * Parameters used when creating the defer queue.
> >>> + */
> >>> +struct rte_rcu_qsbr_dq_parameters {
> >>> +	const char *name;
> >>> +	/**< Name of the queue. */
> >>> +	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 8B as the rte_ring APIs
> >>> +	 *   support 8B element sizes only.
> >>> +	 */
> >>> +	rte_rcu_qsbr_free_resource f;
> >>> +	/**< 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 @@
> >>> -648,6 +710,113 @@ __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.
> >>> + *
> >>> + * This API is not multi-thread safe. It is expected that the
> >>> +caller
> >>> + * provides multi-thread safety by locking a mutex or some other means.
> >>> + *
> >>> + * A lock free multi-thread writer algorithm could achieve
> >>> +multi-thread
> >>> + * safety by creating and using one defer queue per thread.
> >>> + *
> >>> + * @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
> >>> + *
> >>> + * Reclaim resources from the defer queue.
> >>> + *
> >>> + * This API is not multi-thread safe. It is expected that the
> >>> +caller
> >>> + * provides multi-thread safety by locking a mutex or some other means.
> >>> + *
> >>> + * A lock free multi-thread writer algorithm could achieve
> >>> +multi-thread
> >>> + * safety by creating and using one defer queue per thread.
> >>> + *
> >>> + * @param dq
> >>> + *   Defer queue to reclaim an entry from.
> >>> + * @return
> >>> + *   On successful reclamation of at least 1 resource - 0
> >>> + *   On error - 1 with rte_errno set to
> >>> + *   - EINVAL - NULL parameters are passed
> >>> + *   - EAGAIN - None of the resources have completed at least 1 grace
> >> period,
> >>> + *		try again.
> >>> + */
> >>> +__rte_experimental
> >>> +int
> >>> +rte_rcu_qsbr_dq_reclaim(struct rte_rcu_qsbr_dq *dq);
> >>> +
> >>> +/**
> >>> + * @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:
> >>> + *   - EINVAL - NULL parameters are passed
> >>> + *   - 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_qsbr_pvt.h
> >>> b/lib/librte_rcu/rte_rcu_qsbr_pvt.h
> >>> new file mode 100644
> >>> index 000000000..2122bc36a
> >>> --- /dev/null
> >>> +++ b/lib/librte_rcu/rte_rcu_qsbr_pvt.h
> >>> @@ -0,0 +1,46 @@
> >>> +/* SPDX-License-Identifier: BSD-3-Clause
> >>> + * Copyright (c) 2019 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_rcu_qsbr.h"
> >>> +
> >>> +/* 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 {
> >>> +	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 stored on the defer queue */
> >>> +	rte_rcu_qsbr_free_resource f;
> >>> +	/**< 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.
> >>> +	 */
> >>> +	char e[0];
> >>> +	/**< Temporary storage to copy the defer queue element. */ };
> >>> +
> >>> +#ifdef __cplusplus
> >>> +}
> >>> +#endif
> >>> +
> >>> +#endif /* _RTE_RCU_QSBR_PVT_H_ */
> >>> 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
> >>> e5ff83893..0e1be8407 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', 'reorder', 'sched', 'security', 'stack', 'vhost',
> >>> +	'reorder', 'sched', 'security', 'stack', 'vhost',
> >>>    	# ipsec lib depends on net, crypto and security
> >>>    	'ipsec',
> >>>    	# add pkt framework libs which use other libs from above
> >> --
> >> Regards,
> >> Vladimir
> 
> --
> Regards,
> Vladimir