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Diffstat (limited to 'src/vppinfra/slist.c')
| -rw-r--r-- | src/vppinfra/slist.c | 336 |
1 files changed, 0 insertions, 336 deletions
diff --git a/src/vppinfra/slist.c b/src/vppinfra/slist.c deleted file mode 100644 index 5598871c884..00000000000 --- a/src/vppinfra/slist.c +++ /dev/null @@ -1,336 +0,0 @@ -/* - Copyright (c) 2012 Cisco and/or its affiliates. - - * Licensed under the Apache License, Version 2.0 (the "License"); - * you may not use this file except in compliance with the License. - * You may obtain a copy of the License at: - * - * http://www.apache.org/licenses/LICENSE-2.0 - * - * Unless required by applicable law or agreed to in writing, software - * distributed under the License is distributed on an "AS IS" BASIS, - * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. - * See the License for the specific language governing permissions and - * limitations under the License. -*/ - -#include <vppinfra/slist.h> - -/* - * skip-list implementation - * - * Good news / bad news. As balanced binary tree schemes go, - * this one seems pretty fast and is reasonably simple. There's a very - * limited amount that can be done to mitigate sdram read latency. - * - * Each active clib_slist_elt_t is on from 1 to N lists. Each active element - * is always on the "level-0" list. Since most elements are *only* on - * level 0, we keep the level 0 (and level 1) in the element. For those - * elements on more than two lists, we switch to a vector. Hence, the - * "n" union in slib_slist_elt_t. - * - * The low-order bit of elt->n.next0[0] is 1 for inlined next indices, - * 0 for vector indices (since the allocator always aligns to at least - * a 4-byte boundary). We can only represent 2e9 items, but since the - * practical performance limit is O(1e7), it doesn't matter. - * - * We create a "head" element which (by construction) is always - * lexically lighter than any other element. This makes a large number - * of irritating special cases go away. - * - * User code is in charge of comparing a supplied key with - * the key component of a user pool element. The user tells this code - * to add or delete (opaque key, 32-bit integer) pairs to the skip-list. - * - * The algorithm adds new elements to one or more lists. - * For levels greater than zero, the probability of a new element landing on - * a list is branching_factor**N. Branching_factor = 0.2 seems to work - * OK, yielding about 50 compares per search at O(1e7) items. - */ - -clib_error_t * -clib_slist_init (clib_slist_t * sp, f64 branching_factor, - clib_slist_key_compare_function_t compare, - format_function_t format_user_element) -{ - clib_slist_elt_t *head; - clib_memset (sp, 0, sizeof (sp[0])); - sp->branching_factor = branching_factor; - sp->format_user_element = format_user_element; - sp->compare = compare; - sp->seed = 0xdeaddabe; - pool_get (sp->elts, head); - vec_add1 (head->n.nexts, (u32) ~ 0); - head->user_pool_index = (u32) ~ 0; - vec_validate (sp->path, 1); - vec_validate (sp->occupancy, 0); - - return 0; -} - -/* - * slist_search_internal - */ -static inline clib_slist_search_result_t -slist_search_internal (clib_slist_t * sp, void *key, int need_full_path) -{ - int level, comp_result; - clib_slist_elt_t *search_elt, *head_elt; - - sp->ncompares = 0; - /* - * index 0 is the magic listhead element which is - * lexically lighter than / to the left of every element - */ - search_elt = head_elt = pool_elt_at_index (sp->elts, 0); - - /* - * Initial negotiating position, only the head_elt is - * lighter than the supplied key - */ - clib_memset (sp->path, 0, vec_len (head_elt->n.nexts) * sizeof (u32)); - - /* Walk the fastest lane first */ - level = vec_len (head_elt->n.nexts) - 1; - _vec_len (sp->path) = level + 1; - - while (1) - { - u32 next_index_this_level; - clib_slist_elt_t *prefetch_elt; - - /* - * Prefetching the next element at this level makes a measurable - * difference, but doesn't fix the dependent read stall problem - */ - prefetch_elt = sp->elts + - clib_slist_get_next_at_level (search_elt, level); - - CLIB_PREFETCH (prefetch_elt, CLIB_CACHE_LINE_BYTES, READ); - - /* Compare the key with the current element */ - comp_result = (search_elt == head_elt) ? 1 : - sp->compare (key, search_elt->user_pool_index); - - sp->ncompares++; - /* key "lighter" than this element */ - if (comp_result < 0) - { - /* - * Back up to previous item on this list - * and search the next finer-grained list - * starting there. - */ - search_elt = pool_elt_at_index (sp->elts, sp->path[level]); - next_list: - if (level > 0) - { - level--; - continue; - } - else - { - return CLIB_SLIST_NO_MATCH; - } - } - /* Match */ - if (comp_result == 0) - { - /* - * If we're trying to delete an element, we need to - * track down all of the elements which point at it. - * Otherwise, don't bother with it - */ - if (need_full_path && level > 0) - { - search_elt = pool_elt_at_index (sp->elts, sp->path[level]); - level--; - continue; - } - level = vec_len (head_elt->n.nexts); - sp->path[level] = search_elt - sp->elts; - _vec_len (sp->path) = level + 1; - return CLIB_SLIST_MATCH; - } - /* - * comp_result positive, key is to the right of - * this element - */ - sp->path[level] = search_elt - sp->elts; - - /* Out of list at this level? */ - next_index_this_level = - clib_slist_get_next_at_level (search_elt, level); - if (next_index_this_level == (u32) ~ 0) - goto next_list; - - /* No, try the next element */ - search_elt = pool_elt_at_index (sp->elts, next_index_this_level); - } - return 0; /* notreached */ -} - -u32 -clib_slist_search (clib_slist_t * sp, void *key, u32 * ncompares) -{ - clib_slist_search_result_t rv; - - rv = slist_search_internal (sp, key, 0 /* dont need full path */ ); - if (rv == CLIB_SLIST_MATCH) - { - clib_slist_elt_t *elt; - elt = pool_elt_at_index (sp->elts, sp->path[vec_len (sp->path) - 1]); - if (ncompares) - *ncompares = sp->ncompares; - return elt->user_pool_index; - } - return (u32) ~ 0; -} - -void -clib_slist_add (clib_slist_t * sp, void *key, u32 user_pool_index) -{ - clib_slist_elt_t *new_elt; - clib_slist_search_result_t search_result; - int level; - - search_result = slist_search_internal (sp, key, - 0 /* don't need full path */ ); - - /* Special case: key exists, just replace user_pool_index */ - if (PREDICT_FALSE (search_result == CLIB_SLIST_MATCH)) - { - clib_slist_elt_t *elt; - elt = pool_elt_at_index (sp->elts, sp->path[0]); - elt->user_pool_index = user_pool_index; - return; - } - - pool_get (sp->elts, new_elt); - new_elt->n.nexts = 0; - new_elt->user_pool_index = user_pool_index; - - /* sp->path lists elements to the left of key, by level */ - for (level = 0; level < vec_len (sp->path); level++) - { - clib_slist_elt_t *prev_elt_this_level; - u32 prev_elt_next_index_this_level; - - /* Add to list at the current level */ - prev_elt_this_level = pool_elt_at_index (sp->elts, sp->path[level]); - prev_elt_next_index_this_level = clib_slist_get_next_at_level - (prev_elt_this_level, level); - - clib_slist_set_next_at_level (new_elt, prev_elt_next_index_this_level, - level); - - clib_slist_set_next_at_level (prev_elt_this_level, new_elt - sp->elts, - level); - sp->occupancy[level]++; - - /* Randomly add to the next-higher level */ - if (random_f64 (&sp->seed) > sp->branching_factor) - break; - } - { - /* Time to add a new ply? */ - clib_slist_elt_t *head_elt = pool_elt_at_index (sp->elts, 0); - int top_level = vec_len (head_elt->n.nexts) - 1; - if (((f64) sp->occupancy[top_level]) * sp->branching_factor > 1.0) - { - vec_add1 (sp->occupancy, 0); - vec_add1 (head_elt->n.nexts, (u32) ~ 0); - /* full match case returns n+1 items */ - vec_validate (sp->path, vec_len (head_elt->n.nexts)); - } - } -} - -clib_slist_search_result_t -clib_slist_del (clib_slist_t * sp, void *key) -{ - clib_slist_search_result_t search_result; - clib_slist_elt_t *del_elt; - int level; - - search_result = slist_search_internal (sp, key, 1 /* need full path */ ); - - if (PREDICT_FALSE (search_result == CLIB_SLIST_NO_MATCH)) - return search_result; - - del_elt = pool_elt_at_index (sp->elts, sp->path[vec_len (sp->path) - 1]); - ASSERT (vec_len (sp->path) > 1); - - for (level = 0; level < vec_len (sp->path) - 1; level++) - { - clib_slist_elt_t *path_elt; - u32 path_elt_next_index; - - path_elt = pool_elt_at_index (sp->elts, sp->path[level]); - path_elt_next_index = clib_slist_get_next_at_level (path_elt, level); - - /* Splice the item out of the list if it's adjacent to the victim */ - if (path_elt_next_index == del_elt - sp->elts) - { - sp->occupancy[level]--; - path_elt_next_index = clib_slist_get_next_at_level (del_elt, level); - clib_slist_set_next_at_level (path_elt, path_elt_next_index, level); - } - } - - /* If this element is on more than two lists it has a vector of nexts */ - if (!(del_elt->n.next0[0] & 1)) - vec_free (del_elt->n.nexts); - pool_put (sp->elts, del_elt); - return CLIB_SLIST_MATCH; -} - -u8 * -format_slist (u8 * s, va_list * args) -{ - clib_slist_t *sl = va_arg (*args, clib_slist_t *); - int verbose = va_arg (*args, int); - int i; - clib_slist_elt_t *head_elt, *elt; - - s = format (s, "slist 0x%x, %u items, branching_factor %.2f\n", sl, - sl->occupancy ? sl->occupancy[0] : 0, sl->branching_factor); - - if (pool_elts (sl->elts) == 0) - return s; - - head_elt = pool_elt_at_index (sl->elts, 0); - - for (i = 0; i < vec_len (head_elt->n.nexts); i++) - { - s = format (s, "level %d: %d elts\n", i, - sl->occupancy ? sl->occupancy[i] : 0); - - if (verbose && head_elt->n.nexts[i] != (u32) ~ 0) - { - elt = pool_elt_at_index (sl->elts, head_elt->n.nexts[i]); - while (elt) - { - u32 next_index; - s = format (s, "%U(%d) ", sl->format_user_element, - elt->user_pool_index, elt - sl->elts); - next_index = clib_slist_get_next_at_level (elt, i); - ASSERT (next_index != 0x7fffffff); - if (next_index == (u32) ~ 0) - break; - else - elt = pool_elt_at_index (sl->elts, next_index); - } - } - s = format (s, "\n"); - } - return s; -} - -/* - * fd.io coding-style-patch-verification: ON - * - * Local Variables: - * eval: (c-set-style "gnu") - * End: - */ |