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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_SORT_KEYS_MAX 2
17 /*
18 * This is an overview of the tracing_map data structures and how they
19 * relate to the tracing_map API. The details of the algorithms
20 * aren't discussed here - this is just a general overview of the data
21 * structures and how they interact with the API.
22 *
23 * The central data structure of the tracing_map is an initially
24 * zeroed array of struct tracing_map_entry (stored in the map field
25 * of struct tracing_map). tracing_map_entry is a very simple data
26 * structure containing only two fields: a 32-bit unsigned 'key'
27 * variable and a pointer named 'val'. This array of struct
28 * tracing_map_entry is essentially a hash table which will be
29 * modified by a single function, tracing_map_insert(), but which can
30 * be traversed and read by a user at any time (though the user does
31 * this indirectly via an array of tracing_map_sort_entry - see the
32 * explanation of that data structure in the discussion of the
33 * sorting-related data structures below).
34 *
35 * The central function of the tracing_map API is
36 * tracing_map_insert(). tracing_map_insert() hashes the
37 * arbitrarily-sized key passed into it into a 32-bit unsigned key.
38 * It then uses this key, truncated to the array size, as an index
39 * into the array of tracing_map_entries. If the value of the 'key'
40 * field of the tracing_map_entry found at that location is 0, then
41 * that entry is considered to be free and can be claimed, by
42 * replacing the 0 in the 'key' field of the tracing_map_entry with
43 * the new 32-bit hashed key. Once claimed, that tracing_map_entry's
44 * 'val' field is then used to store a unique element which will be
45 * forever associated with that 32-bit hashed key in the
46 * tracing_map_entry.
47 *
48 * That unique element now in the tracing_map_entry's 'val' field is
49 * an instance of tracing_map_elt, where 'elt' in the latter part of
50 * that variable name is short for 'element'. The purpose of a
51 * tracing_map_elt is to hold values specific to the particular
52 * 32-bit hashed key it's assocated with. Things such as the unique
53 * set of aggregated sums associated with the 32-bit hashed key, along
54 * with a copy of the full key associated with the entry, and which
55 * was used to produce the 32-bit hashed key.
56 *
57 * When tracing_map_create() is called to create the tracing map, the
58 * user specifies (indirectly via the map_bits param, the details are
59 * unimportant for this discussion) the maximum number of elements
60 * that the map can hold (stored in the max_elts field of struct
61 * tracing_map). This is the maximum possible number of
62 * tracing_map_entries in the tracing_map_entry array which can be
63 * 'claimed' as described in the above discussion, and therefore is
64 * also the maximum number of tracing_map_elts that can be associated
65 * with the tracing_map_entry array in the tracing_map. Because of
66 * the way the insertion algorithm works, the size of the allocated
67 * tracing_map_entry array is always twice the maximum number of
68 * elements (2 * max_elts). This value is stored in the map_size
69 * field of struct tracing_map.
70 *
71 * Because tracing_map_insert() needs to work from any context,
72 * including from within the memory allocation functions themselves,
73 * both the tracing_map_entry array and a pool of max_elts
74 * tracing_map_elts are pre-allocated before any call is made to
75 * tracing_map_insert().
76 *
77 * The tracing_map_entry array is allocated as a single block by
78 * tracing_map_create().
79 *
80 * Because the tracing_map_elts are much larger objects and can't
81 * generally be allocated together as a single large array without
82 * failure, they're allocated individually, by tracing_map_init().
83 *
84 * The pool of tracing_map_elts are allocated by tracing_map_init()
85 * rather than by tracing_map_create() because at the time
86 * tracing_map_create() is called, there isn't enough information to
87 * create the tracing_map_elts. Specifically,the user first needs to
88 * tell the tracing_map implementation how many fields the
89 * tracing_map_elts contain, and which types of fields they are (key
90 * or sum). The user does this via the tracing_map_add_sum_field()
91 * and tracing_map_add_key_field() functions, following which the user
92 * calls tracing_map_init() to finish up the tracing map setup. The
93 * array holding the pointers which make up the pre-allocated pool of
94 * tracing_map_elts is allocated as a single block and is stored in
95 * the elts field of struct tracing_map.
96 *
97 * There is also a set of structures used for sorting that might
98 * benefit from some minimal explanation.
99 *
100 * struct tracing_map_sort_key is used to drive the sort at any given
101 * time. By 'any given time' we mean that a different
102 * tracing_map_sort_key will be used at different times depending on
103 * whether the sort currently being performed is a primary or a
104 * secondary sort.
105 *
106 * The sort key is very simple, consisting of the field index of the
107 * tracing_map_elt field to sort on (which the user saved when adding
108 * the field), and whether the sort should be done in an ascending or
109 * descending order.
110 *
111 * For the convenience of the sorting code, a tracing_map_sort_entry
112 * is created for each tracing_map_elt, again individually allocated
113 * to avoid failures that might be expected if allocated as a single
114 * large array of struct tracing_map_sort_entry.
115 * tracing_map_sort_entry instances are the objects expected by the
116 * various internal sorting functions, and are also what the user
117 * ultimately receives after calling tracing_map_sort_entries().
118 * Because it doesn't make sense for users to access an unordered and
119 * sparsely populated tracing_map directly, the
120 * tracing_map_sort_entries() function is provided so that users can
121 * retrieve a sorted list of all existing elements. In addition to
122 * the associated tracing_map_elt 'elt' field contained within the
123 * tracing_map_sort_entry, which is the object of interest to the
124 * user, tracing_map_sort_entry objects contain a number of additional
125 * fields which are used for caching and internal purposes and can
126 * safely be ignored.
127 */
130 tracing_map_cmp_fn_t cmp_fn;
132 atomic64_t sum;
134 };
135 };
142 };
145 u32 key;
147 };
152 };
159 };
168 };
170 #define TRACING_MAP_ARRAY_ELT(array, idx) \
171 (array->pages[idx >> array->entry_shift] + \
172 ((idx & array->entry_mask) << array->entry_size_shift))
174 #define TRACING_MAP_ENTRY(array, idx) \
175 ((struct tracing_map_entry *)TRACING_MAP_ARRAY_ELT(array, idx))
177 #define TRACING_MAP_ELT(array, idx) \
178 ((struct tracing_map_elt **)TRACING_MAP_ARRAY_ELT(array, idx))
185 atomic_t next_elt;
195 atomic64_t hits;
196 atomic64_t drops;
197 };
199 /**
200 * struct tracing_map_ops - callbacks for tracing_map
201 *
202 * The methods in this structure define callback functions for various
203 * operations on a tracing_map or objects related to a tracing_map.
204 *
205 * For a detailed description of tracing_map_elt objects please see
206 * the overview of tracing_map data structures at the beginning of
207 * this file.
208 *
209 * All the methods below are optional.
210 *
211 * @elt_alloc: When a tracing_map_elt is allocated, this function, if
212 * defined, will be called and gives clients the opportunity to
213 * allocate additional data and attach it to the element
214 * (tracing_map_elt->private_data is meant for that purpose).
215 * Element allocation occurs before tracing begins, when the
216 * tracing_map_init() call is made by client code.
217 *
218 * @elt_copy: At certain points in the lifetime of an element, it may
219 * need to be copied. The copy should include a copy of the
220 * client-allocated data, which can be copied into the 'to'
221 * element from the 'from' element.
222 *
223 * @elt_free: When a tracing_map_elt is freed, this function is called
224 * and allows client-allocated per-element data to be freed.
225 *
226 * @elt_clear: This callback allows per-element client-defined data to
227 * be cleared, if applicable.
228 *
229 * @elt_init: This callback allows per-element client-defined data to
230 * be initialized when used i.e. when the element is actually
231 * claimed by tracing_map_insert() in the context of the map
232 * insertion.
233 */
241 };
253 tracing_map_cmp_fn_t cmp_fn);
274 tracing_map_cmp_fn_t cmp_fn);