[dpdk-dev] [PATCH v3 7/9] ring: introduce peek style API

[Honnappa Nagarahalli]

<snip>

> 
> For rings with producer/consumer in RTE_RING_SYNC_ST,
> RTE_RING_SYNC_MT_HTS mode, provide an ability to split enqueue/dequeue
> operation into two phases:
>       - enqueue/dequeue start
>       - enqueue/dequeue finish
> That allows user to inspect objects in the ring without removing them from it
> (aka MT safe peek).
> 
> Signed-off-by: Konstantin Ananyev <konstantin.ananyev at intel.com>
> ---
>  lib/librte_ring/Makefile               |   1 +
>  lib/librte_ring/meson.build            |   1 +
>  lib/librte_ring/rte_ring_c11_mem.h     |  44 +++
>  lib/librte_ring/rte_ring_elem.h        |   4 +
>  lib/librte_ring/rte_ring_generic.h     |  48 ++++
>  lib/librte_ring/rte_ring_hts_generic.h |  47 ++-
>  lib/librte_ring/rte_ring_peek.h        | 379 +++++++++++++++++++++++++
>  7 files changed, 519 insertions(+), 5 deletions(-)  create mode 100644
> lib/librte_ring/rte_ring_peek.h
> 
> diff --git a/lib/librte_ring/Makefile b/lib/librte_ring/Makefile index
> 6fe500f0d..5f8662737 100644
> --- a/lib/librte_ring/Makefile
> +++ b/lib/librte_ring/Makefile
> @@ -22,6 +22,7 @@ SYMLINK-$(CONFIG_RTE_LIBRTE_RING)-include :=
> rte_ring.h \
>  					rte_ring_hts.h \
>  					rte_ring_hts_elem.h \
>  					rte_ring_hts_generic.h \
> +					rte_ring_peek.h \
>  					rte_ring_rts.h \
>  					rte_ring_rts_elem.h \
>  					rte_ring_rts_generic.h
> diff --git a/lib/librte_ring/meson.build b/lib/librte_ring/meson.build index
> 8e86e037a..f5f84dc6e 100644
> --- a/lib/librte_ring/meson.build
> +++ b/lib/librte_ring/meson.build
> @@ -9,6 +9,7 @@ headers = files('rte_ring.h',
>  		'rte_ring_hts.h',
>  		'rte_ring_hts_elem.h',
>  		'rte_ring_hts_generic.h',
> +		'rte_ring_peek.h',
>  		'rte_ring_rts.h',
>  		'rte_ring_rts_elem.h',
>  		'rte_ring_rts_generic.h')
> diff --git a/lib/librte_ring/rte_ring_c11_mem.h
> b/lib/librte_ring/rte_ring_c11_mem.h
> index 0fb73a337..bb3096721 100644
> --- a/lib/librte_ring/rte_ring_c11_mem.h
> +++ b/lib/librte_ring/rte_ring_c11_mem.h
> @@ -10,6 +10,50 @@
>  #ifndef _RTE_RING_C11_MEM_H_
>  #define _RTE_RING_C11_MEM_H_
> 
> +/**
> + * @internal get current tail value.
> + * This function should be used only for single thread producer/consumer.
> + * Check that user didn't request to move tail above the head.
Do we need this check? This could be a data path function, we could document a warning and leave it to the users to provide the correct value.

> + * In that situation:
> + * - return zero, that will cause abort any pending changes and
> + *   return head to its previous position.
> + * - throw an assert in debug mode.
> + */
> +static __rte_always_inline uint32_t
> +__rte_ring_st_get_tail(struct rte_ring_headtail *ht, uint32_t *tail,
> +	uint32_t num)
> +{
> +	uint32_t h, n, t;
> +
> +	h = ht->head;
> +	t = ht->tail;
> +	n = h - t;
> +
> +	RTE_ASSERT(n >= num);
> +	num = (n >= num) ? num : 0;
> +
> +	*tail = h;
> +	return num;
> +}
> +
> +/**
> + * @internal set new values for head and tail.
> + * This function should be used only for single thread producer/consumer.
> + * Should be used only in conjunction with __rte_ring_st_get_tail.
> + */
> +static __rte_always_inline void
> +__rte_ring_st_set_head_tail(struct rte_ring_headtail *ht, uint32_t tail,
> +	uint32_t num, uint32_t enqueue)
> +{
> +	uint32_t pos;
> +
> +	RTE_SET_USED(enqueue);
> +
> +	pos = tail + num;
> +	ht->head = pos;
> +	__atomic_store_n(&ht->tail, pos, __ATOMIC_RELEASE); }
> +
>  static __rte_always_inline void
>  update_tail(struct rte_ring_headtail *ht, uint32_t old_val, uint32_t new_val,
>  		uint32_t single, uint32_t enqueue)
> diff --git a/lib/librte_ring/rte_ring_elem.h b/lib/librte_ring/rte_ring_elem.h
> index 010a564c1..5bf7c1c1b 100644
> --- a/lib/librte_ring/rte_ring_elem.h
> +++ b/lib/librte_ring/rte_ring_elem.h
> @@ -1083,6 +1083,10 @@ rte_ring_dequeue_burst_elem(struct rte_ring *r,
> void *obj_table,
>  	return 0;
>  }
> 
> +#ifdef ALLOW_EXPERIMENTAL_API
> +#include <rte_ring_peek.h>
> +#endif
> +
>  #ifdef __cplusplus
>  }
>  #endif
> diff --git a/lib/librte_ring/rte_ring_generic.h
> b/lib/librte_ring/rte_ring_generic.h
> index 953cdbbd5..9f5fdf13b 100644
> --- a/lib/librte_ring/rte_ring_generic.h
> +++ b/lib/librte_ring/rte_ring_generic.h
> @@ -10,6 +10,54 @@
>  #ifndef _RTE_RING_GENERIC_H_
>  #define _RTE_RING_GENERIC_H_
> 
> +/**
> + * @internal get current tail value.
> + * This function should be used only for single thread producer/consumer.
> + * Check that user didn't request to move tail above the head.
> + * In that situation:
> + * - return zero, that will cause abort any pending changes and
> + *   return head to its previous position.
> + * - throw an assert in debug mode.
> + */
> +static __rte_always_inline uint32_t
> +__rte_ring_st_get_tail(struct rte_ring_headtail *ht, uint32_t *tail,
> +	uint32_t num)
> +{
> +	uint32_t h, n, t;
> +
> +	h = ht->head;
> +	t = ht->tail;
> +	n = h - t;
> +
> +	RTE_ASSERT(n >= num);
> +	num = (n >= num) ? num : 0;
> +
> +	*tail = h;
> +	return num;
> +}
> +
> +/**
> + * @internal set new values for head and tail.
> + * This function should be used only for single thread producer/consumer.
> + * Should be used only in conjunction with __rte_ring_st_get_tail.
> + */
> +static __rte_always_inline void
> +__rte_ring_st_set_head_tail(struct rte_ring_headtail *ht, uint32_t tail,
> +	uint32_t num, uint32_t enqueue)
> +{
> +	uint32_t pos;
> +
> +	pos = tail + num;
> +
> +	if (enqueue)
> +		rte_smp_wmb();
> +	else
> +		rte_smp_rmb();
> +
> +	ht->head = pos;
> +	ht->tail = pos;
> +}
> +
>  static __rte_always_inline void
>  update_tail(struct rte_ring_headtail *ht, uint32_t old_val, uint32_t new_val,
>  		uint32_t single, uint32_t enqueue)
> diff --git a/lib/librte_ring/rte_ring_hts_generic.h
> b/lib/librte_ring/rte_ring_hts_generic.h
> index da08f1d94..8e699c006 100644
> --- a/lib/librte_ring/rte_ring_hts_generic.h
> +++ b/lib/librte_ring/rte_ring_hts_generic.h
> @@ -18,9 +18,38 @@
>   * For more information please refer to <rte_ring_hts.h>.
>   */
> 
> +/**
> + * @internal get current tail value.
> + * Check that user didn't request to move tail above the head.
> + * In that situation:
> + * - return zero, that will cause abort any pending changes and
> + *   return head to its previous position.
> + * - throw an assert in debug mode.
> + */
> +static __rte_always_inline uint32_t
> +__rte_ring_hts_get_tail(struct rte_ring_hts_headtail *ht, uint32_t *tail,
> +	uint32_t num)
> +{
> +	uint32_t n;
> +	union rte_ring_ht_pos p;
> +
> +	p.raw = rte_atomic64_read((rte_atomic64_t *)(uintptr_t)&ht-
> >ht.raw);
> +	n = p.pos.head - p.pos.tail;
> +
> +	RTE_ASSERT(n >= num);
> +	num = (n >= num) ? num : 0;
> +
> +	*tail = p.pos.tail;
> +	return num;
> +}
> +
> +/**
> + * @internal set new values for head and tail as one atomic 64 bit operation.
> + * Should be used only in conjunction with __rte_ring_hts_get_tail.
> + */
>  static __rte_always_inline void
> -__rte_ring_hts_update_tail(struct rte_ring_hts_headtail *ht, uint32_t num,
> -	uint32_t enqueue)
> +__rte_ring_hts_set_head_tail(struct rte_ring_hts_headtail *ht, uint32_t tail,
> +	uint32_t num, uint32_t enqueue)
>  {
>  	union rte_ring_ht_pos p;
> 
> @@ -29,14 +58,22 @@ __rte_ring_hts_update_tail(struct
> rte_ring_hts_headtail *ht, uint32_t num,
>  	else
>  		rte_smp_rmb();
> 
> -	p.raw = rte_atomic64_read((rte_atomic64_t *)(uintptr_t)&ht-
> >ht.raw);
> -
> -	p.pos.head = p.pos.tail + num;
> +	p.pos.head = tail + num;
>  	p.pos.tail = p.pos.head;
> 
>  	rte_atomic64_set((rte_atomic64_t *)(uintptr_t)&ht->ht.raw, p.raw);  }
> 
> +static __rte_always_inline void
> +__rte_ring_hts_update_tail(struct rte_ring_hts_headtail *ht, uint32_t num,
> +	uint32_t enqueue)
> +{
> +	uint32_t tail;
> +
> +	num = __rte_ring_hts_get_tail(ht, &tail, num);
> +	__rte_ring_hts_set_head_tail(ht, tail, num, enqueue); }
> +
>  /**
>   * @internal waits till tail will become equal to head.
>   * Means no writer/reader is active for that ring.
> diff --git a/lib/librte_ring/rte_ring_peek.h b/lib/librte_ring/rte_ring_peek.h
> new file mode 100644 index 000000000..baefd2f7b
> --- /dev/null
> +++ b/lib/librte_ring/rte_ring_peek.h
> @@ -0,0 +1,379 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + *
> + * Copyright (c) 2010-2017 Intel Corporation
> + * 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_H_
> +#define _RTE_RING_PEEK_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 AP
                            ^^^ API
> + * Introduction of rte_ring with serialized producer/consumer (HTS sync
> +mode)
> + * makes possible to split public enqueue/dequeue API into two phases:
> + * - enqueue/dequeue start
> + * - enqueue/dequeue finish
> + * That allows user to inspect objects in the ring without removing
> +them
> + * from it (aka MT safe peek).
> + * Note that right now this new API is avaialble 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.
> + * As an example:
> + * // read 1 elem from the ring:
> + * n = rte_ring_hts_dequeue_bulk_start(ring, &obj, 1, NULL);
> + * if (n != 0) {
> + *    //examine object
> + *    if (object_examine(obj) == KEEP)
> + *       //decided to keep it in the ring.
> + *       rte_ring_hts_dequeue_finish(ring, 0);
> + *    else
> + *       //decided to remove it from the ring.
> + *       rte_ring_hts_dequeue_finish(ring, n);
> + * }
> + * Note that between _start_ and _finish_ the ring is sort of locked -
                                                                                  ^^^^^^^^^^^^^^^^^^^^ - 'locked' can mean different to different people, may be remove this, the next sentence anyway has the description
> + * none other thread can proceed with enqueue(/dequeue) operation till
          ^^^^ no
> + * _finish_ will complete.
                         ^^^^^^^^^^^ completes
> + */
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif
> +

<snip>

> +
> +/**
> + * Start to enqueue several objects on the ring.
> + * Note that no actual objects are put in the queue by this function,
> + * it just reserves for user such ability.
> + * User has to call appropriate enqueue_finish() to copy objects into
> +the
> + * queue and complete given enqueue operation.
> + *
> + * @param r
> + *   A pointer to the ring structure.
> + * @param n
> + *   The number of objects to add in the ring from the obj_table.
> + * @param free_space
> + *   if non-NULL, returns the amount of space in the ring after the
> + *   enqueue 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_bulk_start(struct rte_ring *r, unsigned int n,
> +		unsigned int *free_space)
If one wants to use _elem_ APIs for ring peek, a combination of legacy API (format) and a _elem_ API is required.
For ex:
rte_ring_enqueue_bulk_start
rte_ring_enqueue_elem_finish

I understand why you have done this. I think this is getting somewhat too inconsistent.

> +{
> +	return __rte_ring_do_enqueue_start(r, n, RTE_RING_QUEUE_FIXED,
> +			free_space);
> +}
> +

<snip>

> +
> +/**
> + * Start to dequeue several objects from the ring.
> + * Note that user has to call appropriate dequeue_finish()
> + * to complete given dequeue operation and actually remove objects the ring.
> + *
> + * @param r
> + *   A pointer to the ring structure.
> + * @param obj_table
> + *   A pointer to a table of void * pointers (objects) that will be filled.
> + * @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 to the obj_table.
> + * @param available
> + *   If non-NULL, returns the number of remaining ring entries after the
> + *   dequeue has finished.
> + * @return
> + *   Actual number of objects dequeued.
> + */
> +__rte_experimental
> +static __rte_always_inline unsigned int
> +rte_ring_dequeue_bulk_start(struct rte_ring *r, void **obj_table,
> +		unsigned int n, unsigned int *available) {
Should this in a separate file? (similar to rte_ring.h and rte_ring_elem.h)

> +	return rte_ring_dequeue_bulk_elem_start(r, obj_table,
> sizeof(uintptr_t),
> +		n, available);
> +}
> +
> +/**
> + * Start to dequeue several objects from the ring.
> + * Note that user has to call appropriate dequeue_finish()
> + * to complete given dequeue operation and actually remove objects the ring.
> + *
> + * @param r
> + *   A pointer to the ring structure.
> + * @param obj_table
> + *   A pointer to a table of void * pointers (objects) that will be filled.
Minor, update this to indicate generic objects. Can be copied from rte_ring_elem.h.

> + * @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 to the obj_table.
> + * @param available
> + *   If non-NULL, returns the number of remaining ring entries after the
> + *   dequeue has finished.
> + * @return
> + *   The actual number of objects dequeued.
> + */
> +__rte_experimental
> +static __rte_always_inline unsigned int
> +rte_ring_dequeue_burst_elem_start(struct rte_ring *r, void **obj_table,
> +		unsigned int esize, unsigned int n, unsigned int *available) {
> +	return __rte_ring_do_dequeue_start(r, obj_table, esize, n,
> +			RTE_RING_QUEUE_VARIABLE, available); }
> +

<snip>

> +
> +#ifdef __cplusplus
> +}
> +#endif
> +
> +#endif /* _RTE_RING_PEEK_H_ */
> --
> 2.17.1