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1 // SPDX-License-Identifier: GPL-2.0
2 #ifndef __TRACING_MAP_H
3 #define __TRACING_MAP_H
5 #define TRACING_MAP_BITS_DEFAULT 11
6 #define TRACING_MAP_BITS_MAX 17
7 #define TRACING_MAP_BITS_MIN 7
9 #define TRACING_MAP_KEYS_MAX 3
10 #define TRACING_MAP_VALS_MAX 3
11 #define TRACING_MAP_FIELDS_MAX (TRACING_MAP_KEYS_MAX + \
12 TRACING_MAP_VALS_MAX)
13 #define TRACING_MAP_VARS_MAX 16
14 #define TRACING_MAP_SORT_KEYS_MAX 2
18 /*
19 * This is an overview of the tracing_map data structures and how they
20 * relate to the tracing_map API. The details of the algorithms
21 * aren't discussed here - this is just a general overview of the data
22 * structures and how they interact with the API.
23 *
24 * The central data structure of the tracing_map is an initially
25 * zeroed array of struct tracing_map_entry (stored in the map field
26 * of struct tracing_map). tracing_map_entry is a very simple data
27 * structure containing only two fields: a 32-bit unsigned 'key'
28 * variable and a pointer named 'val'. This array of struct
29 * tracing_map_entry is essentially a hash table which will be
30 * modified by a single function, tracing_map_insert(), but which can
31 * be traversed and read by a user at any time (though the user does
32 * this indirectly via an array of tracing_map_sort_entry - see the
33 * explanation of that data structure in the discussion of the
34 * sorting-related data structures below).
35 *
36 * The central function of the tracing_map API is
37 * tracing_map_insert(). tracing_map_insert() hashes the
38 * arbitrarily-sized key passed into it into a 32-bit unsigned key.
39 * It then uses this key, truncated to the array size, as an index
40 * into the array of tracing_map_entries. If the value of the 'key'
41 * field of the tracing_map_entry found at that location is 0, then
42 * that entry is considered to be free and can be claimed, by
43 * replacing the 0 in the 'key' field of the tracing_map_entry with
44 * the new 32-bit hashed key. Once claimed, that tracing_map_entry's
45 * 'val' field is then used to store a unique element which will be
46 * forever associated with that 32-bit hashed key in the
47 * tracing_map_entry.
48 *
49 * That unique element now in the tracing_map_entry's 'val' field is
50 * an instance of tracing_map_elt, where 'elt' in the latter part of
51 * that variable name is short for 'element'. The purpose of a
52 * tracing_map_elt is to hold values specific to the particular
53 * 32-bit hashed key it's associated with. Things such as the unique
54 * set of aggregated sums associated with the 32-bit hashed key, along
55 * with a copy of the full key associated with the entry, and which
56 * was used to produce the 32-bit hashed key.
57 *
58 * When tracing_map_create() is called to create the tracing map, the
59 * user specifies (indirectly via the map_bits param, the details are
60 * unimportant for this discussion) the maximum number of elements
61 * that the map can hold (stored in the max_elts field of struct
62 * tracing_map). This is the maximum possible number of
63 * tracing_map_entries in the tracing_map_entry array which can be
64 * 'claimed' as described in the above discussion, and therefore is
65 * also the maximum number of tracing_map_elts that can be associated
66 * with the tracing_map_entry array in the tracing_map. Because of
67 * the way the insertion algorithm works, the size of the allocated
68 * tracing_map_entry array is always twice the maximum number of
69 * elements (2 * max_elts). This value is stored in the map_size
70 * field of struct tracing_map.
71 *
72 * Because tracing_map_insert() needs to work from any context,
73 * including from within the memory allocation functions themselves,
74 * both the tracing_map_entry array and a pool of max_elts
75 * tracing_map_elts are pre-allocated before any call is made to
76 * tracing_map_insert().
77 *
78 * The tracing_map_entry array is allocated as a single block by
79 * tracing_map_create().
80 *
81 * Because the tracing_map_elts are much larger objects and can't
82 * generally be allocated together as a single large array without
83 * failure, they're allocated individually, by tracing_map_init().
84 *
85 * The pool of tracing_map_elts are allocated by tracing_map_init()
86 * rather than by tracing_map_create() because at the time
87 * tracing_map_create() is called, there isn't enough information to
88 * create the tracing_map_elts. Specifically,the user first needs to
89 * tell the tracing_map implementation how many fields the
90 * tracing_map_elts contain, and which types of fields they are (key
91 * or sum). The user does this via the tracing_map_add_sum_field()
92 * and tracing_map_add_key_field() functions, following which the user
93 * calls tracing_map_init() to finish up the tracing map setup. The
94 * array holding the pointers which make up the pre-allocated pool of
95 * tracing_map_elts is allocated as a single block and is stored in
96 * the elts field of struct tracing_map.
97 *
98 * There is also a set of structures used for sorting that might
99 * benefit from some minimal explanation.
100 *
101 * struct tracing_map_sort_key is used to drive the sort at any given
102 * time. By 'any given time' we mean that a different
103 * tracing_map_sort_key will be used at different times depending on
104 * whether the sort currently being performed is a primary or a
105 * secondary sort.
106 *
107 * The sort key is very simple, consisting of the field index of the
108 * tracing_map_elt field to sort on (which the user saved when adding
109 * the field), and whether the sort should be done in an ascending or
110 * descending order.
111 *
112 * For the convenience of the sorting code, a tracing_map_sort_entry
113 * is created for each tracing_map_elt, again individually allocated
114 * to avoid failures that might be expected if allocated as a single
115 * large array of struct tracing_map_sort_entry.
116 * tracing_map_sort_entry instances are the objects expected by the
117 * various internal sorting functions, and are also what the user
118 * ultimately receives after calling tracing_map_sort_entries().
119 * Because it doesn't make sense for users to access an unordered and
120 * sparsely populated tracing_map directly, the
121 * tracing_map_sort_entries() function is provided so that users can
122 * retrieve a sorted list of all existing elements. In addition to
123 * the associated tracing_map_elt 'elt' field contained within the
124 * tracing_map_sort_entry, which is the object of interest to the
125 * user, tracing_map_sort_entry objects contain a number of additional
126 * fields which are used for caching and internal purposes and can
127 * safely be ignored.
128 */
131 tracing_map_cmp_fn_t cmp_fn;
133 atomic64_t sum;
135 };
136 };
145 };
148 u32 key;
150 };
155 };
162 };
171 };
173 #define TRACING_MAP_ARRAY_ELT(array, idx) \
174 (array->pages[idx >> array->entry_shift] + \
175 ((idx & array->entry_mask) << array->entry_size_shift))
177 #define TRACING_MAP_ENTRY(array, idx) \
178 ((struct tracing_map_entry *)TRACING_MAP_ARRAY_ELT(array, idx))
180 #define TRACING_MAP_ELT(array, idx) \
181 ((struct tracing_map_elt **)TRACING_MAP_ARRAY_ELT(array, idx))
188 atomic_t next_elt;
199 atomic64_t hits;
200 atomic64_t drops;
201 };
203 /**
204 * struct tracing_map_ops - callbacks for tracing_map
205 *
206 * The methods in this structure define callback functions for various
207 * operations on a tracing_map or objects related to a tracing_map.
208 *
209 * For a detailed description of tracing_map_elt objects please see
210 * the overview of tracing_map data structures at the beginning of
211 * this file.
212 *
213 * All the methods below are optional.
214 *
215 * @elt_alloc: When a tracing_map_elt is allocated, this function, if
216 * defined, will be called and gives clients the opportunity to
217 * allocate additional data and attach it to the element
218 * (tracing_map_elt->private_data is meant for that purpose).
219 * Element allocation occurs before tracing begins, when the
220 * tracing_map_init() call is made by client code.
221 *
222 * @elt_free: When a tracing_map_elt is freed, this function is called
223 * and allows client-allocated per-element data to be freed.
224 *
225 * @elt_clear: This callback allows per-element client-defined data to
226 * be cleared, if applicable.
227 *
228 * @elt_init: This callback allows per-element client-defined data to
229 * be initialized when used i.e. when the element is actually
230 * claimed by tracing_map_insert() in the context of the map
231 * insertion.
232 */
238 };
251 tracing_map_cmp_fn_t cmp_fn);
278 tracing_map_cmp_fn_t cmp_fn);