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-rw-r--r--src/vppinfra/slist.c336
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diff --git a/src/vppinfra/slist.c b/src/vppinfra/slist.c
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--- a/src/vppinfra/slist.c
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-/*
- 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:
- */