| 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) 1999-2016 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 | /* The type used to hold a single bcache string. The user data is |
| 27 | stored in d.data. Since it can be any type, it needs to have the |
| 28 | same alignment as the most strict alignment of any type on the host |
| 29 | machine. I don't know of any really correct way to do this in |
| 30 | stock ANSI C, so just do it the same way obstack.h does. */ |
| 31 | |
| 32 | struct bstring |
| 33 | { |
| 34 | /* Hash chain. */ |
| 35 | struct bstring *next; |
| 36 | /* Assume the data length is no more than 64k. */ |
| 37 | unsigned short length; |
| 38 | /* The half hash hack. This contains the upper 16 bits of the hash |
| 39 | value and is used as a pre-check when comparing two strings and |
| 40 | avoids the need to do length or memcmp calls. It proves to be |
| 41 | roughly 100% effective. */ |
| 42 | unsigned short half_hash; |
| 43 | |
| 44 | union |
| 45 | { |
| 46 | char data[1]; |
| 47 | double dummy; |
| 48 | } |
| 49 | d; |
| 50 | }; |
| 51 | |
| 52 | |
| 53 | /* The structure for a bcache itself. The bcache is initialized, in |
| 54 | bcache_xmalloc(), by filling it with zeros and then setting the |
| 55 | corresponding obstack's malloc() and free() methods. */ |
| 56 | |
| 57 | struct bcache |
| 58 | { |
| 59 | /* All the bstrings are allocated here. */ |
| 60 | struct obstack cache; |
| 61 | |
| 62 | /* How many hash buckets we're using. */ |
| 63 | unsigned int num_buckets; |
| 64 | |
| 65 | /* Hash buckets. This table is allocated using malloc, so when we |
| 66 | grow the table we can return the old table to the system. */ |
| 67 | struct bstring **bucket; |
| 68 | |
| 69 | /* Statistics. */ |
| 70 | unsigned long unique_count; /* number of unique strings */ |
| 71 | long total_count; /* total number of strings cached, including dups */ |
| 72 | long unique_size; /* size of unique strings, in bytes */ |
| 73 | long total_size; /* total number of bytes cached, including dups */ |
| 74 | long structure_size; /* total size of bcache, including infrastructure */ |
| 75 | /* Number of times that the hash table is expanded and hence |
| 76 | re-built, and the corresponding number of times that a string is |
| 77 | [re]hashed as part of entering it into the expanded table. The |
| 78 | total number of hashes can be computed by adding TOTAL_COUNT to |
| 79 | expand_hash_count. */ |
| 80 | unsigned long expand_count; |
| 81 | unsigned long expand_hash_count; |
| 82 | /* Number of times that the half-hash compare hit (compare the upper |
| 83 | 16 bits of hash values) hit, but the corresponding combined |
| 84 | length/data compare missed. */ |
| 85 | unsigned long half_hash_miss_count; |
| 86 | |
| 87 | /* Hash function to be used for this bcache object. */ |
| 88 | unsigned long (*hash_function)(const void *addr, int length); |
| 89 | |
| 90 | /* Compare function to be used for this bcache object. */ |
| 91 | int (*compare_function)(const void *, const void *, int length); |
| 92 | }; |
| 93 | |
| 94 | /* The old hash function was stolen from SDBM. This is what DB 3.0 |
| 95 | uses now, and is better than the old one. */ |
| 96 | \f |
| 97 | unsigned long |
| 98 | hash(const void *addr, int length) |
| 99 | { |
| 100 | return hash_continue (addr, length, 0); |
| 101 | } |
| 102 | |
| 103 | /* Continue the calculation of the hash H at the given address. */ |
| 104 | |
| 105 | unsigned long |
| 106 | hash_continue (const void *addr, int length, unsigned long h) |
| 107 | { |
| 108 | const unsigned char *k, *e; |
| 109 | |
| 110 | k = (const unsigned char *)addr; |
| 111 | e = k+length; |
| 112 | for (; k< e;++k) |
| 113 | { |
| 114 | h *=16777619; |
| 115 | h ^= *k; |
| 116 | } |
| 117 | return (h); |
| 118 | } |
| 119 | \f |
| 120 | /* Growing the bcache's hash table. */ |
| 121 | |
| 122 | /* If the average chain length grows beyond this, then we want to |
| 123 | resize our hash table. */ |
| 124 | #define CHAIN_LENGTH_THRESHOLD (5) |
| 125 | |
| 126 | static void |
| 127 | expand_hash_table (struct bcache *bcache) |
| 128 | { |
| 129 | /* A table of good hash table sizes. Whenever we grow, we pick the |
| 130 | next larger size from this table. sizes[i] is close to 1 << (i+10), |
| 131 | so we roughly double the table size each time. After we fall off |
| 132 | the end of this table, we just double. Don't laugh --- there have |
| 133 | been executables sighted with a gigabyte of debug info. */ |
| 134 | static unsigned long sizes[] = { |
| 135 | 1021, 2053, 4099, 8191, 16381, 32771, |
| 136 | 65537, 131071, 262144, 524287, 1048573, 2097143, |
| 137 | 4194301, 8388617, 16777213, 33554467, 67108859, 134217757, |
| 138 | 268435459, 536870923, 1073741827, 2147483659UL |
| 139 | }; |
| 140 | unsigned int new_num_buckets; |
| 141 | struct bstring **new_buckets; |
| 142 | unsigned int i; |
| 143 | |
| 144 | /* Count the stats. Every unique item needs to be re-hashed and |
| 145 | re-entered. */ |
| 146 | bcache->expand_count++; |
| 147 | bcache->expand_hash_count += bcache->unique_count; |
| 148 | |
| 149 | /* Find the next size. */ |
| 150 | new_num_buckets = bcache->num_buckets * 2; |
| 151 | for (i = 0; i < (sizeof (sizes) / sizeof (sizes[0])); i++) |
| 152 | if (sizes[i] > bcache->num_buckets) |
| 153 | { |
| 154 | new_num_buckets = sizes[i]; |
| 155 | break; |
| 156 | } |
| 157 | |
| 158 | /* Allocate the new table. */ |
| 159 | { |
| 160 | size_t new_size = new_num_buckets * sizeof (new_buckets[0]); |
| 161 | |
| 162 | new_buckets = (struct bstring **) xmalloc (new_size); |
| 163 | memset (new_buckets, 0, new_size); |
| 164 | |
| 165 | bcache->structure_size -= (bcache->num_buckets |
| 166 | * sizeof (bcache->bucket[0])); |
| 167 | bcache->structure_size += new_size; |
| 168 | } |
| 169 | |
| 170 | /* Rehash all existing strings. */ |
| 171 | for (i = 0; i < bcache->num_buckets; i++) |
| 172 | { |
| 173 | struct bstring *s, *next; |
| 174 | |
| 175 | for (s = bcache->bucket[i]; s; s = next) |
| 176 | { |
| 177 | struct bstring **new_bucket; |
| 178 | next = s->next; |
| 179 | |
| 180 | new_bucket = &new_buckets[(bcache->hash_function (&s->d.data, |
| 181 | s->length) |
| 182 | % new_num_buckets)]; |
| 183 | s->next = *new_bucket; |
| 184 | *new_bucket = s; |
| 185 | } |
| 186 | } |
| 187 | |
| 188 | /* Plug in the new table. */ |
| 189 | if (bcache->bucket) |
| 190 | xfree (bcache->bucket); |
| 191 | bcache->bucket = new_buckets; |
| 192 | bcache->num_buckets = new_num_buckets; |
| 193 | } |
| 194 | |
| 195 | \f |
| 196 | /* Looking up things in the bcache. */ |
| 197 | |
| 198 | /* The number of bytes needed to allocate a struct bstring whose data |
| 199 | is N bytes long. */ |
| 200 | #define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n)) |
| 201 | |
| 202 | /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has |
| 203 | never seen those bytes before, add a copy of them to BCACHE. In |
| 204 | either case, return a pointer to BCACHE's copy of that string. */ |
| 205 | const void * |
| 206 | bcache (const void *addr, int length, struct bcache *cache) |
| 207 | { |
| 208 | return bcache_full (addr, length, cache, NULL); |
| 209 | } |
| 210 | |
| 211 | /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has |
| 212 | never seen those bytes before, add a copy of them to BCACHE. In |
| 213 | either case, return a pointer to BCACHE's copy of that string. If |
| 214 | optional ADDED is not NULL, return 1 in case of new entry or 0 if |
| 215 | returning an old entry. */ |
| 216 | |
| 217 | const void * |
| 218 | bcache_full (const void *addr, int length, struct bcache *bcache, int *added) |
| 219 | { |
| 220 | unsigned long full_hash; |
| 221 | unsigned short half_hash; |
| 222 | int hash_index; |
| 223 | struct bstring *s; |
| 224 | |
| 225 | if (added) |
| 226 | *added = 0; |
| 227 | |
| 228 | /* Lazily initialize the obstack. This can save quite a bit of |
| 229 | memory in some cases. */ |
| 230 | if (bcache->total_count == 0) |
| 231 | { |
| 232 | /* We could use obstack_specify_allocation here instead, but |
| 233 | gdb_obstack.h specifies the allocation/deallocation |
| 234 | functions. */ |
| 235 | obstack_init (&bcache->cache); |
| 236 | } |
| 237 | |
| 238 | /* If our average chain length is too high, expand the hash table. */ |
| 239 | if (bcache->unique_count >= bcache->num_buckets * CHAIN_LENGTH_THRESHOLD) |
| 240 | expand_hash_table (bcache); |
| 241 | |
| 242 | bcache->total_count++; |
| 243 | bcache->total_size += length; |
| 244 | |
| 245 | full_hash = bcache->hash_function (addr, length); |
| 246 | |
| 247 | half_hash = (full_hash >> 16); |
| 248 | hash_index = full_hash % bcache->num_buckets; |
| 249 | |
| 250 | /* Search the hash bucket for a string identical to the caller's. |
| 251 | As a short-circuit first compare the upper part of each hash |
| 252 | values. */ |
| 253 | for (s = bcache->bucket[hash_index]; s; s = s->next) |
| 254 | { |
| 255 | if (s->half_hash == half_hash) |
| 256 | { |
| 257 | if (s->length == length |
| 258 | && bcache->compare_function (&s->d.data, addr, length)) |
| 259 | return &s->d.data; |
| 260 | else |
| 261 | bcache->half_hash_miss_count++; |
| 262 | } |
| 263 | } |
| 264 | |
| 265 | /* The user's string isn't in the list. Insert it after *ps. */ |
| 266 | { |
| 267 | struct bstring *newobj |
| 268 | = (struct bstring *) obstack_alloc (&bcache->cache, |
| 269 | BSTRING_SIZE (length)); |
| 270 | |
| 271 | memcpy (&newobj->d.data, addr, length); |
| 272 | newobj->length = length; |
| 273 | newobj->next = bcache->bucket[hash_index]; |
| 274 | newobj->half_hash = half_hash; |
| 275 | bcache->bucket[hash_index] = newobj; |
| 276 | |
| 277 | bcache->unique_count++; |
| 278 | bcache->unique_size += length; |
| 279 | bcache->structure_size += BSTRING_SIZE (length); |
| 280 | |
| 281 | if (added) |
| 282 | *added = 1; |
| 283 | |
| 284 | return &newobj->d.data; |
| 285 | } |
| 286 | } |
| 287 | \f |
| 288 | |
| 289 | /* Compare the byte string at ADDR1 of lenght LENGHT to the |
| 290 | string at ADDR2. Return 1 if they are equal. */ |
| 291 | |
| 292 | static int |
| 293 | bcache_compare (const void *addr1, const void *addr2, int length) |
| 294 | { |
| 295 | return memcmp (addr1, addr2, length) == 0; |
| 296 | } |
| 297 | |
| 298 | /* Allocating and freeing bcaches. */ |
| 299 | |
| 300 | /* Allocated a bcache. HASH_FUNCTION and COMPARE_FUNCTION can be used |
| 301 | to pass in custom hash, and compare functions to be used by this |
| 302 | bcache. If HASH_FUNCTION is NULL hash() is used and if |
| 303 | COMPARE_FUNCTION is NULL memcmp() is used. */ |
| 304 | |
| 305 | struct bcache * |
| 306 | bcache_xmalloc (unsigned long (*hash_function)(const void *, int length), |
| 307 | int (*compare_function)(const void *, |
| 308 | const void *, |
| 309 | int length)) |
| 310 | { |
| 311 | /* Allocate the bcache pre-zeroed. */ |
| 312 | struct bcache *b = XCNEW (struct bcache); |
| 313 | |
| 314 | if (hash_function) |
| 315 | b->hash_function = hash_function; |
| 316 | else |
| 317 | b->hash_function = hash; |
| 318 | |
| 319 | if (compare_function) |
| 320 | b->compare_function = compare_function; |
| 321 | else |
| 322 | b->compare_function = bcache_compare; |
| 323 | return b; |
| 324 | } |
| 325 | |
| 326 | /* Free all the storage associated with BCACHE. */ |
| 327 | void |
| 328 | bcache_xfree (struct bcache *bcache) |
| 329 | { |
| 330 | if (bcache == NULL) |
| 331 | return; |
| 332 | /* Only free the obstack if we actually initialized it. */ |
| 333 | if (bcache->total_count > 0) |
| 334 | obstack_free (&bcache->cache, 0); |
| 335 | xfree (bcache->bucket); |
| 336 | xfree (bcache); |
| 337 | } |
| 338 | |
| 339 | |
| 340 | \f |
| 341 | /* Printing statistics. */ |
| 342 | |
| 343 | static void |
| 344 | print_percentage (int portion, int total) |
| 345 | { |
| 346 | if (total == 0) |
| 347 | /* i18n: Like "Percentage of duplicates, by count: (not applicable)". */ |
| 348 | printf_filtered (_("(not applicable)\n")); |
| 349 | else |
| 350 | printf_filtered ("%3d%%\n", (int) (portion * 100.0 / total)); |
| 351 | } |
| 352 | |
| 353 | |
| 354 | /* Print statistics on BCACHE's memory usage and efficacity at |
| 355 | eliminating duplication. NAME should describe the kind of data |
| 356 | BCACHE holds. Statistics are printed using `printf_filtered' and |
| 357 | its ilk. */ |
| 358 | void |
| 359 | print_bcache_statistics (struct bcache *c, char *type) |
| 360 | { |
| 361 | int occupied_buckets; |
| 362 | int max_chain_length; |
| 363 | int median_chain_length; |
| 364 | int max_entry_size; |
| 365 | int median_entry_size; |
| 366 | |
| 367 | /* Count the number of occupied buckets, tally the various string |
| 368 | lengths, and measure chain lengths. */ |
| 369 | { |
| 370 | unsigned int b; |
| 371 | int *chain_length = XCNEWVEC (int, c->num_buckets + 1); |
| 372 | int *entry_size = XCNEWVEC (int, c->unique_count + 1); |
| 373 | int stringi = 0; |
| 374 | |
| 375 | occupied_buckets = 0; |
| 376 | |
| 377 | for (b = 0; b < c->num_buckets; b++) |
| 378 | { |
| 379 | struct bstring *s = c->bucket[b]; |
| 380 | |
| 381 | chain_length[b] = 0; |
| 382 | |
| 383 | if (s) |
| 384 | { |
| 385 | occupied_buckets++; |
| 386 | |
| 387 | while (s) |
| 388 | { |
| 389 | gdb_assert (b < c->num_buckets); |
| 390 | chain_length[b]++; |
| 391 | gdb_assert (stringi < c->unique_count); |
| 392 | entry_size[stringi++] = s->length; |
| 393 | s = s->next; |
| 394 | } |
| 395 | } |
| 396 | } |
| 397 | |
| 398 | /* To compute the median, we need the set of chain lengths |
| 399 | sorted. */ |
| 400 | qsort (chain_length, c->num_buckets, sizeof (chain_length[0]), |
| 401 | compare_positive_ints); |
| 402 | qsort (entry_size, c->unique_count, sizeof (entry_size[0]), |
| 403 | compare_positive_ints); |
| 404 | |
| 405 | if (c->num_buckets > 0) |
| 406 | { |
| 407 | max_chain_length = chain_length[c->num_buckets - 1]; |
| 408 | median_chain_length = chain_length[c->num_buckets / 2]; |
| 409 | } |
| 410 | else |
| 411 | { |
| 412 | max_chain_length = 0; |
| 413 | median_chain_length = 0; |
| 414 | } |
| 415 | if (c->unique_count > 0) |
| 416 | { |
| 417 | max_entry_size = entry_size[c->unique_count - 1]; |
| 418 | median_entry_size = entry_size[c->unique_count / 2]; |
| 419 | } |
| 420 | else |
| 421 | { |
| 422 | max_entry_size = 0; |
| 423 | median_entry_size = 0; |
| 424 | } |
| 425 | |
| 426 | xfree (chain_length); |
| 427 | xfree (entry_size); |
| 428 | } |
| 429 | |
| 430 | printf_filtered (_(" Cached '%s' statistics:\n"), type); |
| 431 | printf_filtered (_(" Total object count: %ld\n"), c->total_count); |
| 432 | printf_filtered (_(" Unique object count: %lu\n"), c->unique_count); |
| 433 | printf_filtered (_(" Percentage of duplicates, by count: ")); |
| 434 | print_percentage (c->total_count - c->unique_count, c->total_count); |
| 435 | printf_filtered ("\n"); |
| 436 | |
| 437 | printf_filtered (_(" Total object size: %ld\n"), c->total_size); |
| 438 | printf_filtered (_(" Unique object size: %ld\n"), c->unique_size); |
| 439 | printf_filtered (_(" Percentage of duplicates, by size: ")); |
| 440 | print_percentage (c->total_size - c->unique_size, c->total_size); |
| 441 | printf_filtered ("\n"); |
| 442 | |
| 443 | printf_filtered (_(" Max entry size: %d\n"), max_entry_size); |
| 444 | printf_filtered (_(" Average entry size: ")); |
| 445 | if (c->unique_count > 0) |
| 446 | printf_filtered ("%ld\n", c->unique_size / c->unique_count); |
| 447 | else |
| 448 | /* i18n: "Average entry size: (not applicable)". */ |
| 449 | printf_filtered (_("(not applicable)\n")); |
| 450 | printf_filtered (_(" Median entry size: %d\n"), median_entry_size); |
| 451 | printf_filtered ("\n"); |
| 452 | |
| 453 | printf_filtered (_(" \ |
| 454 | Total memory used by bcache, including overhead: %ld\n"), |
| 455 | c->structure_size); |
| 456 | printf_filtered (_(" Percentage memory overhead: ")); |
| 457 | print_percentage (c->structure_size - c->unique_size, c->unique_size); |
| 458 | printf_filtered (_(" Net memory savings: ")); |
| 459 | print_percentage (c->total_size - c->structure_size, c->total_size); |
| 460 | printf_filtered ("\n"); |
| 461 | |
| 462 | printf_filtered (_(" Hash table size: %3d\n"), |
| 463 | c->num_buckets); |
| 464 | printf_filtered (_(" Hash table expands: %lu\n"), |
| 465 | c->expand_count); |
| 466 | printf_filtered (_(" Hash table hashes: %lu\n"), |
| 467 | c->total_count + c->expand_hash_count); |
| 468 | printf_filtered (_(" Half hash misses: %lu\n"), |
| 469 | c->half_hash_miss_count); |
| 470 | printf_filtered (_(" Hash table population: ")); |
| 471 | print_percentage (occupied_buckets, c->num_buckets); |
| 472 | printf_filtered (_(" Median hash chain length: %3d\n"), |
| 473 | median_chain_length); |
| 474 | printf_filtered (_(" Average hash chain length: ")); |
| 475 | if (c->num_buckets > 0) |
| 476 | printf_filtered ("%3lu\n", c->unique_count / c->num_buckets); |
| 477 | else |
| 478 | /* i18n: "Average hash chain length: (not applicable)". */ |
| 479 | printf_filtered (_("(not applicable)\n")); |
| 480 | printf_filtered (_(" Maximum hash chain length: %3d\n"), |
| 481 | max_chain_length); |
| 482 | printf_filtered ("\n"); |
| 483 | } |
| 484 | |
| 485 | int |
| 486 | bcache_memory_used (struct bcache *bcache) |
| 487 | { |
| 488 | if (bcache->total_count == 0) |
| 489 | return 0; |
| 490 | return obstack_memory_used (&bcache->cache); |
| 491 | } |