From: Honnappa Nagarahalli Date: Fri, 31 Jan 2020 03:59:29 +0000 (-0600) Subject: doc: update ring guide X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=e89680d024dd3a99830450192b03f404d6c0199e;p=dpdk.git doc: update ring guide Changed the rte_ring chapter in programmer's guide to reflect the addition of rte_ring_xxx_elem APIs. References to pointers as ring elements is changed to generic term 'objects'. Signed-off-by: Honnappa Nagarahalli Reviewed-by: Gavin Hu --- diff --git a/doc/guides/prog_guide/ring_lib.rst b/doc/guides/prog_guide/ring_lib.rst index 5a9b6137e7..8cb2b2dd4c 100644 --- a/doc/guides/prog_guide/ring_lib.rst +++ b/doc/guides/prog_guide/ring_lib.rst @@ -11,7 +11,9 @@ Instead of having a linked list of infinite size, the rte_ring has the following * FIFO -* Maximum size is fixed, the pointers are stored in a table +* Maximum size is fixed, the objects are stored in a table + +* Objects can be pointers or elements of multiple of 4 byte size * Lockless implementation @@ -29,19 +31,19 @@ Instead of having a linked list of infinite size, the rte_ring has the following The advantages of this data structure over a linked list queue are as follows: -* Faster; only requires a single Compare-And-Swap instruction of sizeof(void \*) instead of several double-Compare-And-Swap instructions. +* Faster; only requires a single 32 bit Compare-And-Swap instruction instead of several pointer size Compare-And-Swap instructions. * Simpler than a full lockless queue. * Adapted to bulk enqueue/dequeue operations. - As pointers are stored in a table, a dequeue of several objects will not produce as many cache misses as in a linked queue. + As objects are stored in a table, a dequeue of several objects will not produce as many cache misses as in a linked queue. Also, a bulk dequeue of many objects does not cost more than a dequeue of a simple object. The disadvantages: * Size is fixed -* Having many rings costs more in terms of memory than a linked list queue. An empty ring contains at least N pointers. +* Having many rings costs more in terms of memory than a linked list queue. An empty ring contains at least N objects. A simplified representation of a Ring is shown in with consumer and producer head and tail pointers to objects stored in the data structure. @@ -125,7 +127,7 @@ Enqueue Second Step The second step is to modify *ring->prod_head* in ring structure to point to the same location as prod_next. -A pointer to the added object is copied in the ring (obj4). +The added object is copied in the ring (obj4). .. _figure_ring-enqueue2: @@ -178,7 +180,7 @@ Dequeue Second Step The second step is to modify ring->cons_head in the ring structure to point to the same location as cons_next. -The pointer to the dequeued object (obj1) is copied in the pointer given by the user. +The dequeued object (obj1) is copied in the pointer given by the user. .. _figure_ring-dequeue2: @@ -298,7 +300,7 @@ Modulo 32-bit Indexes In the preceding figures, the prod_head, prod_tail, cons_head and cons_tail indexes are represented by arrows. In the actual implementation, these values are not between 0 and size(ring)-1 as would be assumed. -The indexes are between 0 and 2^32 -1, and we mask their value when we access the pointer table (the ring itself). +The indexes are between 0 and 2^32 -1, and we mask their value when we access the object table (the ring itself). 32-bit modulo also implies that operations on indexes (such as, add/subtract) will automatically do 2^32 modulo if the result overflows the 32-bit number range.