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, 2000, 2002, 2003, 2007, 2008, 2009, 2010 6 Free Software Foundation, Inc. 7 8 This file is part of GDB. 9 10 This program is free software; you can redistribute it and/or modify 11 it under the terms of the GNU General Public License as published by 12 the Free Software Foundation; either version 3 of the License, or 13 (at your option) any later version. 14 15 This program is distributed in the hope that it will be useful, 16 but WITHOUT ANY WARRANTY; without even the implied warranty of 17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 18 GNU General Public License for more details. 19 20 You should have received a copy of the GNU General Public License 21 along with this program. If not, see <http://www.gnu.org/licenses/>. */ 22 23 #include "defs.h" 24 #include "gdb_obstack.h" 25 #include "bcache.h" 26 #include "gdb_string.h" /* For memcpy declaration */ 27 #include "gdb_assert.h" 28 29 #include <stddef.h> 30 #include <stdlib.h> 31 32 /* The type used to hold a single bcache string. The user data is 33 stored in d.data. Since it can be any type, it needs to have the 34 same alignment as the most strict alignment of any type on the host 35 machine. I don't know of any really correct way to do this in 36 stock ANSI C, so just do it the same way obstack.h does. */ 37 38 struct bstring 39 { 40 /* Hash chain. */ 41 struct bstring *next; 42 /* Assume the data length is no more than 64k. */ 43 unsigned short length; 44 /* The half hash hack. This contains the upper 16 bits of the hash 45 value and is used as a pre-check when comparing two strings and 46 avoids the need to do length or memcmp calls. It proves to be 47 roughly 100% effective. */ 48 unsigned short half_hash; 49 50 union 51 { 52 char data[1]; 53 double dummy; 54 } 55 d; 56 }; 57 58 59 /* The structure for a bcache itself. The bcache is initialized, in 60 bcache_xmalloc(), by filling it with zeros and then setting the 61 corresponding obstack's malloc() and free() methods. */ 62 63 struct bcache 64 { 65 /* All the bstrings are allocated here. */ 66 struct obstack cache; 67 68 /* How many hash buckets we're using. */ 69 unsigned int num_buckets; 70 71 /* Hash buckets. This table is allocated using malloc, so when we 72 grow the table we can return the old table to the system. */ 73 struct bstring **bucket; 74 75 /* Statistics. */ 76 unsigned long unique_count; /* number of unique strings */ 77 long total_count; /* total number of strings cached, including dups */ 78 long unique_size; /* size of unique strings, in bytes */ 79 long total_size; /* total number of bytes cached, including dups */ 80 long structure_size; /* total size of bcache, including infrastructure */ 81 /* Number of times that the hash table is expanded and hence 82 re-built, and the corresponding number of times that a string is 83 [re]hashed as part of entering it into the expanded table. The 84 total number of hashes can be computed by adding TOTAL_COUNT to 85 expand_hash_count. */ 86 unsigned long expand_count; 87 unsigned long expand_hash_count; 88 /* Number of times that the half-hash compare hit (compare the upper 89 16 bits of hash values) hit, but the corresponding combined 90 length/data compare missed. */ 91 unsigned long half_hash_miss_count; 92 }; 93 94 /* The old hash function was stolen from SDBM. This is what DB 3.0 uses now, 95 * and is better than the old one. 96 */ 97 98 unsigned long 99 hash(const void *addr, int length) 100 { 101 const unsigned char *k, *e; 102 unsigned long h; 103 104 k = (const unsigned char *)addr; 105 e = k+length; 106 for (h=0; k< e;++k) 107 { 108 h *=16777619; 109 h ^= *k; 110 } 111 return (h); 112 } 113 114 /* Growing the bcache's hash table. */ 115 116 /* If the average chain length grows beyond this, then we want to 117 resize our hash table. */ 118 #define CHAIN_LENGTH_THRESHOLD (5) 119 120 static void 121 expand_hash_table (struct bcache *bcache) 122 { 123 /* A table of good hash table sizes. Whenever we grow, we pick the 124 next larger size from this table. sizes[i] is close to 1 << (i+10), 125 so we roughly double the table size each time. After we fall off 126 the end of this table, we just double. Don't laugh --- there have 127 been executables sighted with a gigabyte of debug info. */ 128 static unsigned long sizes[] = { 129 1021, 2053, 4099, 8191, 16381, 32771, 130 65537, 131071, 262144, 524287, 1048573, 2097143, 131 4194301, 8388617, 16777213, 33554467, 67108859, 134217757, 132 268435459, 536870923, 1073741827, 2147483659UL 133 }; 134 unsigned int new_num_buckets; 135 struct bstring **new_buckets; 136 unsigned int i; 137 138 /* Count the stats. Every unique item needs to be re-hashed and 139 re-entered. */ 140 bcache->expand_count++; 141 bcache->expand_hash_count += bcache->unique_count; 142 143 /* Find the next size. */ 144 new_num_buckets = bcache->num_buckets * 2; 145 for (i = 0; i < (sizeof (sizes) / sizeof (sizes[0])); i++) 146 if (sizes[i] > bcache->num_buckets) 147 { 148 new_num_buckets = sizes[i]; 149 break; 150 } 151 152 /* Allocate the new table. */ 153 { 154 size_t new_size = new_num_buckets * sizeof (new_buckets[0]); 155 156 new_buckets = (struct bstring **) xmalloc (new_size); 157 memset (new_buckets, 0, new_size); 158 159 bcache->structure_size -= (bcache->num_buckets 160 * sizeof (bcache->bucket[0])); 161 bcache->structure_size += new_size; 162 } 163 164 /* Rehash all existing strings. */ 165 for (i = 0; i < bcache->num_buckets; i++) 166 { 167 struct bstring *s, *next; 168 169 for (s = bcache->bucket[i]; s; s = next) 170 { 171 struct bstring **new_bucket; 172 next = s->next; 173 174 new_bucket = &new_buckets[(hash (&s->d.data, s->length) 175 % new_num_buckets)]; 176 s->next = *new_bucket; 177 *new_bucket = s; 178 } 179 } 180 181 /* Plug in the new table. */ 182 if (bcache->bucket) 183 xfree (bcache->bucket); 184 bcache->bucket = new_buckets; 185 bcache->num_buckets = new_num_buckets; 186 } 187 188 189 /* Looking up things in the bcache. */ 190 191 /* The number of bytes needed to allocate a struct bstring whose data 192 is N bytes long. */ 193 #define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n)) 194 195 /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has 196 never seen those bytes before, add a copy of them to BCACHE. In 197 either case, return a pointer to BCACHE's copy of that string. */ 198 const void * 199 bcache (const void *addr, int length, struct bcache *bcache) 200 { 201 return bcache_full (addr, length, bcache, NULL); 202 } 203 204 /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has 205 never seen those bytes before, add a copy of them to BCACHE. In 206 either case, return a pointer to BCACHE's copy of that string. If 207 optional ADDED is not NULL, return 1 in case of new entry or 0 if 208 returning an old entry. */ 209 210 const void * 211 bcache_full (const void *addr, int length, struct bcache *bcache, int *added) 212 { 213 unsigned long full_hash; 214 unsigned short half_hash; 215 int hash_index; 216 struct bstring *s; 217 218 if (added) 219 *added = 0; 220 221 /* Lazily initialize the obstack. This can save quite a bit of 222 memory in some cases. */ 223 if (bcache->total_count == 0) 224 { 225 /* We could use obstack_specify_allocation here instead, but 226 gdb_obstack.h specifies the allocation/deallocation 227 functions. */ 228 obstack_init (&bcache->cache); 229 } 230 231 /* If our average chain length is too high, expand the hash table. */ 232 if (bcache->unique_count >= bcache->num_buckets * CHAIN_LENGTH_THRESHOLD) 233 expand_hash_table (bcache); 234 235 bcache->total_count++; 236 bcache->total_size += length; 237 238 full_hash = hash (addr, length); 239 half_hash = (full_hash >> 16); 240 hash_index = full_hash % bcache->num_buckets; 241 242 /* Search the hash bucket for a string identical to the caller's. 243 As a short-circuit first compare the upper part of each hash 244 values. */ 245 for (s = bcache->bucket[hash_index]; s; s = s->next) 246 { 247 if (s->half_hash == half_hash) 248 { 249 if (s->length == length 250 && ! memcmp (&s->d.data, addr, length)) 251 return &s->d.data; 252 else 253 bcache->half_hash_miss_count++; 254 } 255 } 256 257 /* The user's string isn't in the list. Insert it after *ps. */ 258 { 259 struct bstring *new 260 = obstack_alloc (&bcache->cache, BSTRING_SIZE (length)); 261 262 memcpy (&new->d.data, addr, length); 263 new->length = length; 264 new->next = bcache->bucket[hash_index]; 265 new->half_hash = half_hash; 266 bcache->bucket[hash_index] = new; 267 268 bcache->unique_count++; 269 bcache->unique_size += length; 270 bcache->structure_size += BSTRING_SIZE (length); 271 272 if (added) 273 *added = 1; 274 275 return &new->d.data; 276 } 277 } 278 279 /* Allocating and freeing bcaches. */ 280 281 struct bcache * 282 bcache_xmalloc (void) 283 { 284 /* Allocate the bcache pre-zeroed. */ 285 struct bcache *b = XCALLOC (1, struct bcache); 286 287 return b; 288 } 289 290 /* Free all the storage associated with BCACHE. */ 291 void 292 bcache_xfree (struct bcache *bcache) 293 { 294 if (bcache == NULL) 295 return; 296 /* Only free the obstack if we actually initialized it. */ 297 if (bcache->total_count > 0) 298 obstack_free (&bcache->cache, 0); 299 xfree (bcache->bucket); 300 xfree (bcache); 301 } 302 303 304 305 /* Printing statistics. */ 306 307 static void 308 print_percentage (int portion, int total) 309 { 310 if (total == 0) 311 /* i18n: Like "Percentage of duplicates, by count: (not applicable)" */ 312 printf_filtered (_("(not applicable)\n")); 313 else 314 printf_filtered ("%3d%%\n", (int) (portion * 100.0 / total)); 315 } 316 317 318 /* Print statistics on BCACHE's memory usage and efficacity at 319 eliminating duplication. NAME should describe the kind of data 320 BCACHE holds. Statistics are printed using `printf_filtered' and 321 its ilk. */ 322 void 323 print_bcache_statistics (struct bcache *c, char *type) 324 { 325 int occupied_buckets; 326 int max_chain_length; 327 int median_chain_length; 328 int max_entry_size; 329 int median_entry_size; 330 331 /* Count the number of occupied buckets, tally the various string 332 lengths, and measure chain lengths. */ 333 { 334 unsigned int b; 335 int *chain_length = XCALLOC (c->num_buckets + 1, int); 336 int *entry_size = XCALLOC (c->unique_count + 1, int); 337 int stringi = 0; 338 339 occupied_buckets = 0; 340 341 for (b = 0; b < c->num_buckets; b++) 342 { 343 struct bstring *s = c->bucket[b]; 344 345 chain_length[b] = 0; 346 347 if (s) 348 { 349 occupied_buckets++; 350 351 while (s) 352 { 353 gdb_assert (b < c->num_buckets); 354 chain_length[b]++; 355 gdb_assert (stringi < c->unique_count); 356 entry_size[stringi++] = s->length; 357 s = s->next; 358 } 359 } 360 } 361 362 /* To compute the median, we need the set of chain lengths sorted. */ 363 qsort (chain_length, c->num_buckets, sizeof (chain_length[0]), 364 compare_positive_ints); 365 qsort (entry_size, c->unique_count, sizeof (entry_size[0]), 366 compare_positive_ints); 367 368 if (c->num_buckets > 0) 369 { 370 max_chain_length = chain_length[c->num_buckets - 1]; 371 median_chain_length = chain_length[c->num_buckets / 2]; 372 } 373 else 374 { 375 max_chain_length = 0; 376 median_chain_length = 0; 377 } 378 if (c->unique_count > 0) 379 { 380 max_entry_size = entry_size[c->unique_count - 1]; 381 median_entry_size = entry_size[c->unique_count / 2]; 382 } 383 else 384 { 385 max_entry_size = 0; 386 median_entry_size = 0; 387 } 388 389 xfree (chain_length); 390 xfree (entry_size); 391 } 392 393 printf_filtered (_(" Cached '%s' statistics:\n"), type); 394 printf_filtered (_(" Total object count: %ld\n"), c->total_count); 395 printf_filtered (_(" Unique object count: %lu\n"), c->unique_count); 396 printf_filtered (_(" Percentage of duplicates, by count: ")); 397 print_percentage (c->total_count - c->unique_count, c->total_count); 398 printf_filtered ("\n"); 399 400 printf_filtered (_(" Total object size: %ld\n"), c->total_size); 401 printf_filtered (_(" Unique object size: %ld\n"), c->unique_size); 402 printf_filtered (_(" Percentage of duplicates, by size: ")); 403 print_percentage (c->total_size - c->unique_size, c->total_size); 404 printf_filtered ("\n"); 405 406 printf_filtered (_(" Max entry size: %d\n"), max_entry_size); 407 printf_filtered (_(" Average entry size: ")); 408 if (c->unique_count > 0) 409 printf_filtered ("%ld\n", c->unique_size / c->unique_count); 410 else 411 /* i18n: "Average entry size: (not applicable)" */ 412 printf_filtered (_("(not applicable)\n")); 413 printf_filtered (_(" Median entry size: %d\n"), median_entry_size); 414 printf_filtered ("\n"); 415 416 printf_filtered (_(" Total memory used by bcache, including overhead: %ld\n"), 417 c->structure_size); 418 printf_filtered (_(" Percentage memory overhead: ")); 419 print_percentage (c->structure_size - c->unique_size, c->unique_size); 420 printf_filtered (_(" Net memory savings: ")); 421 print_percentage (c->total_size - c->structure_size, c->total_size); 422 printf_filtered ("\n"); 423 424 printf_filtered (_(" Hash table size: %3d\n"), c->num_buckets); 425 printf_filtered (_(" Hash table expands: %lu\n"), 426 c->expand_count); 427 printf_filtered (_(" Hash table hashes: %lu\n"), 428 c->total_count + c->expand_hash_count); 429 printf_filtered (_(" Half hash misses: %lu\n"), 430 c->half_hash_miss_count); 431 printf_filtered (_(" Hash table population: ")); 432 print_percentage (occupied_buckets, c->num_buckets); 433 printf_filtered (_(" Median hash chain length: %3d\n"), 434 median_chain_length); 435 printf_filtered (_(" Average hash chain length: ")); 436 if (c->num_buckets > 0) 437 printf_filtered ("%3lu\n", c->unique_count / c->num_buckets); 438 else 439 /* i18n: "Average hash chain length: (not applicable)" */ 440 printf_filtered (_("(not applicable)\n")); 441 printf_filtered (_(" Maximum hash chain length: %3d\n"), max_chain_length); 442 printf_filtered ("\n"); 443 } 444 445 int 446 bcache_memory_used (struct bcache *bcache) 447 { 448 if (bcache->total_count == 0) 449 return 0; 450 return obstack_memory_used (&bcache->cache); 451 } 452