1 #include <stdio.h>
2 #include <string.h>
3 #include "../flist.h"
4 #include "../log.h"
5
6 #define MAX_LIST_LENGTH_BITS 20
7
8 /*
9 * Returns a list organized in an intermediate format suited
10 * to chaining of merge() calls: null-terminated, no reserved or
11 * sentinel head node, "prev" links not maintained.
12 */
merge(void * priv,int (* cmp)(void * priv,struct flist_head * a,struct flist_head * b),struct flist_head * a,struct flist_head * b)13 static struct flist_head *merge(void *priv,
14 int (*cmp)(void *priv, struct flist_head *a,
15 struct flist_head *b),
16 struct flist_head *a, struct flist_head *b)
17 {
18 struct flist_head head, *tail = &head;
19
20 while (a && b) {
21 /* if equal, take 'a' -- important for sort stability */
22 if ((*cmp)(priv, a, b) <= 0) {
23 tail->next = a;
24 a = a->next;
25 } else {
26 tail->next = b;
27 b = b->next;
28 }
29 tail = tail->next;
30 }
31 tail->next = a?:b;
32 return head.next;
33 }
34
35 /*
36 * Combine final list merge with restoration of standard doubly-linked
37 * list structure. This approach duplicates code from merge(), but
38 * runs faster than the tidier alternatives of either a separate final
39 * prev-link restoration pass, or maintaining the prev links
40 * throughout.
41 */
merge_and_restore_back_links(void * priv,int (* cmp)(void * priv,struct flist_head * a,struct flist_head * b),struct flist_head * head,struct flist_head * a,struct flist_head * b)42 static void merge_and_restore_back_links(void *priv,
43 int (*cmp)(void *priv, struct flist_head *a,
44 struct flist_head *b),
45 struct flist_head *head,
46 struct flist_head *a, struct flist_head *b)
47 {
48 struct flist_head *tail = head;
49
50 while (a && b) {
51 /* if equal, take 'a' -- important for sort stability */
52 if ((*cmp)(priv, a, b) <= 0) {
53 tail->next = a;
54 a->prev = tail;
55 a = a->next;
56 } else {
57 tail->next = b;
58 b->prev = tail;
59 b = b->next;
60 }
61 tail = tail->next;
62 }
63 tail->next = a ? : b;
64
65 do {
66 /*
67 * In worst cases this loop may run many iterations.
68 * Continue callbacks to the client even though no
69 * element comparison is needed, so the client's cmp()
70 * routine can invoke cond_resched() periodically.
71 */
72 (*cmp)(priv, tail->next, tail->next);
73
74 tail->next->prev = tail;
75 tail = tail->next;
76 } while (tail->next);
77
78 tail->next = head;
79 head->prev = tail;
80 }
81
82 /**
83 * list_sort - sort a list
84 * @priv: private data, opaque to list_sort(), passed to @cmp
85 * @head: the list to sort
86 * @cmp: the elements comparison function
87 *
88 * This function implements "merge sort", which has O(nlog(n))
89 * complexity.
90 *
91 * The comparison function @cmp must return a negative value if @a
92 * should sort before @b, and a positive value if @a should sort after
93 * @b. If @a and @b are equivalent, and their original relative
94 * ordering is to be preserved, @cmp must return 0.
95 */
flist_sort(void * priv,struct flist_head * head,int (* cmp)(void * priv,struct flist_head * a,struct flist_head * b))96 void flist_sort(void *priv, struct flist_head *head,
97 int (*cmp)(void *priv, struct flist_head *a,
98 struct flist_head *b))
99 {
100 struct flist_head *part[MAX_LIST_LENGTH_BITS+1]; /* sorted partial lists
101 -- last slot is a sentinel */
102 int lev; /* index into part[] */
103 int max_lev = 0;
104 struct flist_head *list;
105
106 if (flist_empty(head))
107 return;
108
109 memset(part, 0, sizeof(part));
110
111 head->prev->next = NULL;
112 list = head->next;
113
114 while (list) {
115 struct flist_head *cur = list;
116 list = list->next;
117 cur->next = NULL;
118
119 for (lev = 0; part[lev]; lev++) {
120 cur = merge(priv, cmp, part[lev], cur);
121 part[lev] = NULL;
122 }
123 if (lev > max_lev) {
124 if (lev >= MAX_LIST_LENGTH_BITS) {
125 log_err("fio: list passed to"
126 " list_sort() too long for"
127 " efficiency\n");
128 lev--;
129 }
130 max_lev = lev;
131 }
132 part[lev] = cur;
133 }
134
135 for (lev = 0; lev < max_lev; lev++)
136 if (part[lev])
137 list = merge(priv, cmp, part[lev], list);
138
139 merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
140 }
141