diff options
Diffstat (limited to 'docs/gettingstarted/developers')
| -rw-r--r-- | docs/gettingstarted/developers/bihash.md | 38 |
1 files changed, 19 insertions, 19 deletions
diff --git a/docs/gettingstarted/developers/bihash.md b/docs/gettingstarted/developers/bihash.md index 3754d5f9fa3..b0f98869887 100644 --- a/docs/gettingstarted/developers/bihash.md +++ b/docs/gettingstarted/developers/bihash.md @@ -11,17 +11,17 @@ implementation: * Template implementation, it's easy to support arbitrary (key,value) types Bounded-index extensible hashing has been widely used in databases for -decades. +decades. Bihash uses a two-level data structure: ``` - +-----------------+ - | bucket-0 | - | log2_size | - | backing store | - +-----------------+ - | bucket-1 | + +-----------------+ + | bucket-0 | + | log2_size | + | backing store | + +-----------------+ + | bucket-1 | | log2_size | +--------------------------------+ | backing store | --------> | KVP_PER_PAGE * key-value-pairs | +-----------------+ | page 0 | @@ -29,12 +29,12 @@ Bihash uses a two-level data structure: +-----------------+ | KVP_PER_PAGE * key-value-pairs | | bucket-2**N-1 | | page 1 | | log2_size | +--------------------------------+ - | backing store | --- + | backing store | --- +-----------------+ +--------------------------------+ | KVP_PER_PAGE * key-value-pairs | | page 2**(log2(size)) - 1 | +--------------------------------+ -``` +``` Discussion of the algorithm --------------------------- @@ -105,7 +105,7 @@ often in a subsystem header file: If you're building a standalone application, you'll need to define the various functions by #including the method implementation file in a C -source file. +source file. The core vpp engine currently uses most if not all of the known bihash types, so you probably won't need to #include the method @@ -123,9 +123,9 @@ Add an instance of the selected bihash data structure to e.g. a typedef struct { ... - BVT (clib_bihash) hash; + BVT (clib_bihash) hash_table; or - clib_bihash_8_8_t hash; + clib_bihash_8_8_t hash_table; ... } my_main_t; ``` @@ -147,7 +147,7 @@ stand no chance of working. Call the init function as shown. As a rough guide, pick a number of buckets which is approximately number_of_expected_records/BIHASH_KVP_PER_PAGE from the relevant -template instance header-file. See previous discussion. +template instance header-file. See previous discussion. The amount of memory selected should easily contain all of the records, with a generous allowance for hash collisions. Bihash memory @@ -160,10 +160,10 @@ For example: ```c my_main_t *mm = &my_main; clib_bihash_8_8_t *h; - + h = &mm->hash_table; - clib_bihash_init_8_8 (h, "test", (u32) number_of_buckets, + clib_bihash_init_8_8 (h, "test", (u32) number_of_buckets, (uword) memory_size); ``` @@ -176,7 +176,7 @@ Use BV(clib_bihash_add_del), or the explicit type variant: clib_bihash_8_8_t * h; my_main_t *mm = &my_main; clib_bihash_8_8_t *h; - + h = &mm->hash_table; kv.key = key_to_add_or_delete; kv.value = value_to_add_or_delete; @@ -196,7 +196,7 @@ The simplest possible (key, value) search goes like so: clib_bihash_8_8_t * h; my_main_t *mm = &my_main; clib_bihash_8_8_t *h; - + h = &mm->hash_table; search_kv.key = key_to_add_or_delete; @@ -228,7 +228,7 @@ Dual-loop: * 4 packets ahead, form 2x record keys and call BV(clib_bihash_hash) or the explicit hash function to calculate the record hashes. Call 2x BV(clib_bihash_prefetch_bucket) to prefetch the buckets -* 2 packets ahead, call 2x BV(clib_bihash_prefetch_data) to prefetch +* 2 packets ahead, call 2x BV(clib_bihash_prefetch_data) to prefetch 2x (key,value) data pages. * In the processing section, call 2x BV(clib_bihash_search_inline_with_hash) to perform the search @@ -270,7 +270,7 @@ For another, the iterator template is not safe under all conditions: iterator checks whether the current bucket has been freed after each _callback_fn(...)_ invocation. -* It is __not OK to add__ entries during a table-walk. +* It is __not OK to add__ entries during a table-walk. The add-during-walk case involves a jackpot: while processing a key-value-pair in a particular bucket, add a certain number of |