diff options
author | Con Kolivas <kernel@kolivas.org> | 2019-10-25 14:00:52 +1100 |
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committer | Con Kolivas <kernel@kolivas.org> | 2019-10-25 17:01:56 +1100 |
commit | 7523eb72b6b9f9289618231aab60efb5577d8f33 (patch) | |
tree | 95bb3c5dcb67fc38d32839dd78aaf59451216ca9 /kernel/skip_list.c | |
parent | 4d856f72c10ecb060868ed10ff1b1453943fc6c8 (diff) |
MultiQueue Skiplist Scheduler v0.195.5.3-muqss-195
Diffstat (limited to 'kernel/skip_list.c')
-rw-r--r-- | kernel/skip_list.c | 148 |
1 files changed, 148 insertions, 0 deletions
diff --git a/kernel/skip_list.c b/kernel/skip_list.c new file mode 100644 index 000000000000..bf5c6e97e139 --- /dev/null +++ b/kernel/skip_list.c @@ -0,0 +1,148 @@ +/* + Copyright (C) 2011,2016 Con Kolivas. + + Code based on example originally by William Pugh. + +Skip Lists are a probabilistic alternative to balanced trees, as +described in the June 1990 issue of CACM and were invented by +William Pugh in 1987. + +A couple of comments about this implementation: +The routine randomLevel has been hard-coded to generate random +levels using p=0.25. It can be easily changed. + +The insertion routine has been implemented so as to use the +dirty hack described in the CACM paper: if a random level is +generated that is more than the current maximum level, the +current maximum level plus one is used instead. + +Levels start at zero and go up to MaxLevel (which is equal to +MaxNumberOfLevels-1). + +The routines defined in this file are: + +init: defines slnode + +new_skiplist: returns a new, empty list + +randomLevel: Returns a random level based on a u64 random seed passed to it. +In MuQSS, the "niffy" time is used for this purpose. + +insert(l,key, value): inserts the binding (key, value) into l. This operation +occurs in O(log n) time. + +delnode(slnode, l, node): deletes any binding of key from the l based on the +actual node value. This operation occurs in O(k) time where k is the +number of levels of the node in question (max 8). The original delete +function occurred in O(log n) time and involved a search. + +MuQSS Notes: In this implementation of skiplists, there are bidirectional +next/prev pointers and the insert function returns a pointer to the actual +node the value is stored. The key here is chosen by the scheduler so as to +sort tasks according to the priority list requirements and is no longer used +by the scheduler after insertion. The scheduler lookup, however, occurs in +O(1) time because it is always the first item in the level 0 linked list. +Since the task struct stores a copy of the node pointer upon skiplist_insert, +it can also remove it much faster than the original implementation with the +aid of prev<->next pointer manipulation and no searching. + +*/ + +#include <linux/slab.h> +#include <linux/skip_list.h> + +#define MaxNumberOfLevels 8 +#define MaxLevel (MaxNumberOfLevels - 1) + +void skiplist_init(skiplist_node *slnode) +{ + int i; + + slnode->key = 0xFFFFFFFFFFFFFFFF; + slnode->level = 0; + slnode->value = NULL; + for (i = 0; i < MaxNumberOfLevels; i++) + slnode->next[i] = slnode->prev[i] = slnode; +} + +skiplist *new_skiplist(skiplist_node *slnode) +{ + skiplist *l = kzalloc(sizeof(skiplist), GFP_ATOMIC); + + BUG_ON(!l); + l->header = slnode; + return l; +} + +void free_skiplist(skiplist *l) +{ + skiplist_node *p, *q; + + p = l->header; + do { + q = p->next[0]; + p->next[0]->prev[0] = q->prev[0]; + skiplist_node_init(p); + p = q; + } while (p != l->header); + kfree(l); +} + +void skiplist_node_init(skiplist_node *node) +{ + memset(node, 0, sizeof(skiplist_node)); +} + +static inline unsigned int randomLevel(const long unsigned int randseed) +{ + return find_first_bit(&randseed, MaxLevel) / 2; +} + +void skiplist_insert(skiplist *l, skiplist_node *node, keyType key, valueType value, unsigned int randseed) +{ + skiplist_node *update[MaxNumberOfLevels]; + skiplist_node *p, *q; + int k = l->level; + + p = l->header; + do { + while (q = p->next[k], q->key <= key) + p = q; + update[k] = p; + } while (--k >= 0); + + ++l->entries; + k = randomLevel(randseed); + if (k > l->level) { + k = ++l->level; + update[k] = l->header; + } + + node->level = k; + node->key = key; + node->value = value; + do { + p = update[k]; + node->next[k] = p->next[k]; + p->next[k] = node; + node->prev[k] = p; + node->next[k]->prev[k] = node; + } while (--k >= 0); +} + +void skiplist_delete(skiplist *l, skiplist_node *node) +{ + int k, m = node->level; + + for (k = 0; k <= m; k++) { + node->prev[k]->next[k] = node->next[k]; + node->next[k]->prev[k] = node->prev[k]; + } + skiplist_node_init(node); + if (m == l->level) { + while (l->header->next[m] == l->header && l->header->prev[m] == l->header && m > 0) + m--; + l->level = m; + } + l->entries--; +} |