| 1 | /* Implement a cached obstack. |
| 2 | Written by Fred Fish <fnf@cygnus.com> |
| 3 | Rewritten by Jim Blandy <jimb@cygnus.com> |
| 4 | |
| 5 | Copyright (C) 1999-2020 Free Software Foundation, Inc. |
| 6 | |
| 7 | This file is part of GDB. |
| 8 | |
| 9 | This program is free software; you can redistribute it and/or modify |
| 10 | it under the terms of the GNU General Public License as published by |
| 11 | the Free Software Foundation; either version 3 of the License, or |
| 12 | (at your option) any later version. |
| 13 | |
| 14 | This program is distributed in the hope that it will be useful, |
| 15 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 16 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 17 | GNU General Public License for more details. |
| 18 | |
| 19 | You should have received a copy of the GNU General Public License |
| 20 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ |
| 21 | |
| 22 | #include "defs.h" |
| 23 | #include "gdb_obstack.h" |
| 24 | #include "bcache.h" |
| 25 | |
| 26 | #include <algorithm> |
| 27 | |
| 28 | namespace gdb { |
| 29 | |
| 30 | /* The type used to hold a single bcache string. The user data is |
| 31 | stored in d.data. Since it can be any type, it needs to have the |
| 32 | same alignment as the most strict alignment of any type on the host |
| 33 | machine. I don't know of any really correct way to do this in |
| 34 | stock ANSI C, so just do it the same way obstack.h does. */ |
| 35 | |
| 36 | struct bstring |
| 37 | { |
| 38 | /* Hash chain. */ |
| 39 | struct bstring *next; |
| 40 | /* Assume the data length is no more than 64k. */ |
| 41 | unsigned short length; |
| 42 | /* The half hash hack. This contains the upper 16 bits of the hash |
| 43 | value and is used as a pre-check when comparing two strings and |
| 44 | avoids the need to do length or memcmp calls. It proves to be |
| 45 | roughly 100% effective. */ |
| 46 | unsigned short half_hash; |
| 47 | |
| 48 | union |
| 49 | { |
| 50 | char data[1]; |
| 51 | double dummy; |
| 52 | } |
| 53 | d; |
| 54 | }; |
| 55 | |
| 56 | \f |
| 57 | /* Growing the bcache's hash table. */ |
| 58 | |
| 59 | /* If the average chain length grows beyond this, then we want to |
| 60 | resize our hash table. */ |
| 61 | #define CHAIN_LENGTH_THRESHOLD (5) |
| 62 | |
| 63 | void |
| 64 | bcache::expand_hash_table () |
| 65 | { |
| 66 | /* A table of good hash table sizes. Whenever we grow, we pick the |
| 67 | next larger size from this table. sizes[i] is close to 1 << (i+10), |
| 68 | so we roughly double the table size each time. After we fall off |
| 69 | the end of this table, we just double. Don't laugh --- there have |
| 70 | been executables sighted with a gigabyte of debug info. */ |
| 71 | static unsigned long sizes[] = { |
| 72 | 1021, 2053, 4099, 8191, 16381, 32771, |
| 73 | 65537, 131071, 262144, 524287, 1048573, 2097143, |
| 74 | 4194301, 8388617, 16777213, 33554467, 67108859, 134217757, |
| 75 | 268435459, 536870923, 1073741827, 2147483659UL |
| 76 | }; |
| 77 | unsigned int new_num_buckets; |
| 78 | struct bstring **new_buckets; |
| 79 | unsigned int i; |
| 80 | |
| 81 | /* Count the stats. Every unique item needs to be re-hashed and |
| 82 | re-entered. */ |
| 83 | m_expand_count++; |
| 84 | m_expand_hash_count += m_unique_count; |
| 85 | |
| 86 | /* Find the next size. */ |
| 87 | new_num_buckets = m_num_buckets * 2; |
| 88 | for (i = 0; i < (sizeof (sizes) / sizeof (sizes[0])); i++) |
| 89 | if (sizes[i] > m_num_buckets) |
| 90 | { |
| 91 | new_num_buckets = sizes[i]; |
| 92 | break; |
| 93 | } |
| 94 | |
| 95 | /* Allocate the new table. */ |
| 96 | { |
| 97 | size_t new_size = new_num_buckets * sizeof (new_buckets[0]); |
| 98 | |
| 99 | new_buckets = (struct bstring **) xmalloc (new_size); |
| 100 | memset (new_buckets, 0, new_size); |
| 101 | |
| 102 | m_structure_size -= m_num_buckets * sizeof (m_bucket[0]); |
| 103 | m_structure_size += new_size; |
| 104 | } |
| 105 | |
| 106 | /* Rehash all existing strings. */ |
| 107 | for (i = 0; i < m_num_buckets; i++) |
| 108 | { |
| 109 | struct bstring *s, *next; |
| 110 | |
| 111 | for (s = m_bucket[i]; s; s = next) |
| 112 | { |
| 113 | struct bstring **new_bucket; |
| 114 | next = s->next; |
| 115 | |
| 116 | new_bucket = &new_buckets[(m_hash_function (&s->d.data, s->length) |
| 117 | % new_num_buckets)]; |
| 118 | s->next = *new_bucket; |
| 119 | *new_bucket = s; |
| 120 | } |
| 121 | } |
| 122 | |
| 123 | /* Plug in the new table. */ |
| 124 | xfree (m_bucket); |
| 125 | m_bucket = new_buckets; |
| 126 | m_num_buckets = new_num_buckets; |
| 127 | } |
| 128 | |
| 129 | \f |
| 130 | /* Looking up things in the bcache. */ |
| 131 | |
| 132 | /* The number of bytes needed to allocate a struct bstring whose data |
| 133 | is N bytes long. */ |
| 134 | #define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n)) |
| 135 | |
| 136 | /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has |
| 137 | never seen those bytes before, add a copy of them to BCACHE. In |
| 138 | either case, return a pointer to BCACHE's copy of that string. If |
| 139 | optional ADDED is not NULL, return 1 in case of new entry or 0 if |
| 140 | returning an old entry. */ |
| 141 | |
| 142 | const void * |
| 143 | bcache::insert (const void *addr, int length, int *added) |
| 144 | { |
| 145 | unsigned long full_hash; |
| 146 | unsigned short half_hash; |
| 147 | int hash_index; |
| 148 | struct bstring *s; |
| 149 | |
| 150 | if (added) |
| 151 | *added = 0; |
| 152 | |
| 153 | /* Lazily initialize the obstack. This can save quite a bit of |
| 154 | memory in some cases. */ |
| 155 | if (m_total_count == 0) |
| 156 | { |
| 157 | /* We could use obstack_specify_allocation here instead, but |
| 158 | gdb_obstack.h specifies the allocation/deallocation |
| 159 | functions. */ |
| 160 | obstack_init (&m_cache); |
| 161 | } |
| 162 | |
| 163 | /* If our average chain length is too high, expand the hash table. */ |
| 164 | if (m_unique_count >= m_num_buckets * CHAIN_LENGTH_THRESHOLD) |
| 165 | expand_hash_table (); |
| 166 | |
| 167 | m_total_count++; |
| 168 | m_total_size += length; |
| 169 | |
| 170 | full_hash = m_hash_function (addr, length); |
| 171 | |
| 172 | half_hash = (full_hash >> 16); |
| 173 | hash_index = full_hash % m_num_buckets; |
| 174 | |
| 175 | /* Search the hash m_bucket for a string identical to the caller's. |
| 176 | As a short-circuit first compare the upper part of each hash |
| 177 | values. */ |
| 178 | for (s = m_bucket[hash_index]; s; s = s->next) |
| 179 | { |
| 180 | if (s->half_hash == half_hash) |
| 181 | { |
| 182 | if (s->length == length |
| 183 | && m_compare_function (&s->d.data, addr, length)) |
| 184 | return &s->d.data; |
| 185 | else |
| 186 | m_half_hash_miss_count++; |
| 187 | } |
| 188 | } |
| 189 | |
| 190 | /* The user's string isn't in the list. Insert it after *ps. */ |
| 191 | { |
| 192 | struct bstring *newobj |
| 193 | = (struct bstring *) obstack_alloc (&m_cache, |
| 194 | BSTRING_SIZE (length)); |
| 195 | |
| 196 | memcpy (&newobj->d.data, addr, length); |
| 197 | newobj->length = length; |
| 198 | newobj->next = m_bucket[hash_index]; |
| 199 | newobj->half_hash = half_hash; |
| 200 | m_bucket[hash_index] = newobj; |
| 201 | |
| 202 | m_unique_count++; |
| 203 | m_unique_size += length; |
| 204 | m_structure_size += BSTRING_SIZE (length); |
| 205 | |
| 206 | if (added) |
| 207 | *added = 1; |
| 208 | |
| 209 | return &newobj->d.data; |
| 210 | } |
| 211 | } |
| 212 | \f |
| 213 | |
| 214 | /* Compare the byte string at ADDR1 of lenght LENGHT to the |
| 215 | string at ADDR2. Return 1 if they are equal. */ |
| 216 | |
| 217 | int |
| 218 | bcache::compare (const void *addr1, const void *addr2, int length) |
| 219 | { |
| 220 | return memcmp (addr1, addr2, length) == 0; |
| 221 | } |
| 222 | |
| 223 | /* Free all the storage associated with BCACHE. */ |
| 224 | bcache::~bcache () |
| 225 | { |
| 226 | /* Only free the obstack if we actually initialized it. */ |
| 227 | if (m_total_count > 0) |
| 228 | obstack_free (&m_cache, 0); |
| 229 | xfree (m_bucket); |
| 230 | } |
| 231 | |
| 232 | |
| 233 | \f |
| 234 | /* Printing statistics. */ |
| 235 | |
| 236 | static void |
| 237 | print_percentage (int portion, int total) |
| 238 | { |
| 239 | if (total == 0) |
| 240 | /* i18n: Like "Percentage of duplicates, by count: (not applicable)". */ |
| 241 | printf_filtered (_("(not applicable)\n")); |
| 242 | else |
| 243 | printf_filtered ("%3d%%\n", (int) (portion * 100.0 / total)); |
| 244 | } |
| 245 | |
| 246 | |
| 247 | /* Print statistics on BCACHE's memory usage and efficacity at |
| 248 | eliminating duplication. NAME should describe the kind of data |
| 249 | BCACHE holds. Statistics are printed using `printf_filtered' and |
| 250 | its ilk. */ |
| 251 | void |
| 252 | bcache::print_statistics (const char *type) |
| 253 | { |
| 254 | int occupied_buckets; |
| 255 | int max_chain_length; |
| 256 | int median_chain_length; |
| 257 | int max_entry_size; |
| 258 | int median_entry_size; |
| 259 | |
| 260 | /* Count the number of occupied buckets, tally the various string |
| 261 | lengths, and measure chain lengths. */ |
| 262 | { |
| 263 | unsigned int b; |
| 264 | int *chain_length = XCNEWVEC (int, m_num_buckets + 1); |
| 265 | int *entry_size = XCNEWVEC (int, m_unique_count + 1); |
| 266 | int stringi = 0; |
| 267 | |
| 268 | occupied_buckets = 0; |
| 269 | |
| 270 | for (b = 0; b < m_num_buckets; b++) |
| 271 | { |
| 272 | struct bstring *s = m_bucket[b]; |
| 273 | |
| 274 | chain_length[b] = 0; |
| 275 | |
| 276 | if (s) |
| 277 | { |
| 278 | occupied_buckets++; |
| 279 | |
| 280 | while (s) |
| 281 | { |
| 282 | gdb_assert (b < m_num_buckets); |
| 283 | chain_length[b]++; |
| 284 | gdb_assert (stringi < m_unique_count); |
| 285 | entry_size[stringi++] = s->length; |
| 286 | s = s->next; |
| 287 | } |
| 288 | } |
| 289 | } |
| 290 | |
| 291 | /* To compute the median, we need the set of chain lengths |
| 292 | sorted. */ |
| 293 | std::sort (chain_length, chain_length + m_num_buckets); |
| 294 | std::sort (entry_size, entry_size + m_unique_count); |
| 295 | |
| 296 | if (m_num_buckets > 0) |
| 297 | { |
| 298 | max_chain_length = chain_length[m_num_buckets - 1]; |
| 299 | median_chain_length = chain_length[m_num_buckets / 2]; |
| 300 | } |
| 301 | else |
| 302 | { |
| 303 | max_chain_length = 0; |
| 304 | median_chain_length = 0; |
| 305 | } |
| 306 | if (m_unique_count > 0) |
| 307 | { |
| 308 | max_entry_size = entry_size[m_unique_count - 1]; |
| 309 | median_entry_size = entry_size[m_unique_count / 2]; |
| 310 | } |
| 311 | else |
| 312 | { |
| 313 | max_entry_size = 0; |
| 314 | median_entry_size = 0; |
| 315 | } |
| 316 | |
| 317 | xfree (chain_length); |
| 318 | xfree (entry_size); |
| 319 | } |
| 320 | |
| 321 | printf_filtered (_(" M_Cached '%s' statistics:\n"), type); |
| 322 | printf_filtered (_(" Total object count: %ld\n"), m_total_count); |
| 323 | printf_filtered (_(" Unique object count: %lu\n"), m_unique_count); |
| 324 | printf_filtered (_(" Percentage of duplicates, by count: ")); |
| 325 | print_percentage (m_total_count - m_unique_count, m_total_count); |
| 326 | printf_filtered ("\n"); |
| 327 | |
| 328 | printf_filtered (_(" Total object size: %ld\n"), m_total_size); |
| 329 | printf_filtered (_(" Unique object size: %ld\n"), m_unique_size); |
| 330 | printf_filtered (_(" Percentage of duplicates, by size: ")); |
| 331 | print_percentage (m_total_size - m_unique_size, m_total_size); |
| 332 | printf_filtered ("\n"); |
| 333 | |
| 334 | printf_filtered (_(" Max entry size: %d\n"), max_entry_size); |
| 335 | printf_filtered (_(" Average entry size: ")); |
| 336 | if (m_unique_count > 0) |
| 337 | printf_filtered ("%ld\n", m_unique_size / m_unique_count); |
| 338 | else |
| 339 | /* i18n: "Average entry size: (not applicable)". */ |
| 340 | printf_filtered (_("(not applicable)\n")); |
| 341 | printf_filtered (_(" Median entry size: %d\n"), median_entry_size); |
| 342 | printf_filtered ("\n"); |
| 343 | |
| 344 | printf_filtered (_(" \ |
| 345 | Total memory used by bcache, including overhead: %ld\n"), |
| 346 | m_structure_size); |
| 347 | printf_filtered (_(" Percentage memory overhead: ")); |
| 348 | print_percentage (m_structure_size - m_unique_size, m_unique_size); |
| 349 | printf_filtered (_(" Net memory savings: ")); |
| 350 | print_percentage (m_total_size - m_structure_size, m_total_size); |
| 351 | printf_filtered ("\n"); |
| 352 | |
| 353 | printf_filtered (_(" Hash table size: %3d\n"), |
| 354 | m_num_buckets); |
| 355 | printf_filtered (_(" Hash table expands: %lu\n"), |
| 356 | m_expand_count); |
| 357 | printf_filtered (_(" Hash table hashes: %lu\n"), |
| 358 | m_total_count + m_expand_hash_count); |
| 359 | printf_filtered (_(" Half hash misses: %lu\n"), |
| 360 | m_half_hash_miss_count); |
| 361 | printf_filtered (_(" Hash table population: ")); |
| 362 | print_percentage (occupied_buckets, m_num_buckets); |
| 363 | printf_filtered (_(" Median hash chain length: %3d\n"), |
| 364 | median_chain_length); |
| 365 | printf_filtered (_(" Average hash chain length: ")); |
| 366 | if (m_num_buckets > 0) |
| 367 | printf_filtered ("%3lu\n", m_unique_count / m_num_buckets); |
| 368 | else |
| 369 | /* i18n: "Average hash chain length: (not applicable)". */ |
| 370 | printf_filtered (_("(not applicable)\n")); |
| 371 | printf_filtered (_(" Maximum hash chain length: %3d\n"), |
| 372 | max_chain_length); |
| 373 | printf_filtered ("\n"); |
| 374 | } |
| 375 | |
| 376 | int |
| 377 | bcache::memory_used () |
| 378 | { |
| 379 | if (m_total_count == 0) |
| 380 | return 0; |
| 381 | return obstack_memory_used (&m_cache); |
| 382 | } |
| 383 | |
| 384 | } /* namespace gdb */ |