gdb/dcache.c

   1 /* Caching code.  Typically used by remote back ends for
   2    caching remote memory.
   3
   4    Copyright 1992-1993, 1995, 1998-1999 Free Software Foundation, Inc.
   5
   6    This file is part of GDB.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 2 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 59 Temple Place - Suite 330,
  21    Boston, MA 02111-1307, USA.  */
  22
  23 #include "defs.h"
  24 #include "dcache.h"
  25 #include "gdbcmd.h"
  26 #include "gdb_string.h"
  27 #include "gdbcore.h"
  28
  29 /*
  30    The data cache could lead to incorrect results because it doesn't know
  31    about volatile variables, thus making it impossible to debug
  32    functions which use memory mapped I/O devices.
  33
  34    set remotecache 0
  35
  36    In those cases.
  37
  38    In general the dcache speeds up performance, some speed improvement
  39    comes from the actual caching mechanism, but the major gain is in
  40    the reduction of the remote protocol overhead; instead of reading
  41    or writing a large area of memory in 4 byte requests, the cache
  42    bundles up the requests into 32 byte (actually LINE_SIZE) chunks.
  43    Reducing the overhead to an eighth of what it was.  This is very
  44    obvious when displaying a large amount of data,
  45
  46    eg, x/200x 0
  47
  48    caching     |   no    yes
  49    ----------------------------
  50    first time  |   4 sec  2 sec improvement due to chunking
  51    second time |   4 sec  0 sec improvement due to caching
  52
  53    The cache structure is unusual, we keep a number of cache blocks
  54    (DCACHE_SIZE) and each one caches a LINE_SIZEed area of memory.
  55    Within each line we remember the address of the line (always a
  56    multiple of the LINE_SIZE) and a vector of bytes over the range.
  57    There's another vector which contains the state of the bytes.
  58
  59    ENTRY_BAD means that the byte is just plain wrong, and has no
  60    correspondence with anything else (as it would when the cache is
  61    turned on, but nothing has been done to it.
  62
  63    ENTRY_DIRTY means that the byte has some data in it which should be
  64    written out to the remote target one day, but contains correct
  65    data.  ENTRY_OK means that the data is the same in the cache as it
  66    is in remote memory.
  67
  68
  69    The ENTRY_DIRTY state is necessary because GDB likes to write large
  70    lumps of memory in small bits.  If the caching mechanism didn't
  71    maintain the DIRTY information, then something like a two byte
  72    write would mean that the entire cache line would have to be read,
  73    the two bytes modified and then written out again.  The alternative
  74    would be to not read in the cache line in the first place, and just
  75    write the two bytes directly into target memory.  The trouble with
  76    that is that it really nails performance, because of the remote
  77    protocol overhead.  This way, all those little writes are bundled
  78    up into an entire cache line write in one go, without having to
  79    read the cache line in the first place.
  80
  81
  82  */
  83
  84
  85 /* This value regulates the number of cache blocks stored.
  86    Smaller values reduce the time spent searching for a cache
  87    line, and reduce memory requirements, but increase the risk
  88    of a line not being in memory */
  89
  90 #define DCACHE_SIZE 64
  91
  92 /* This value regulates the size of a cache line.  Smaller values
  93    reduce the time taken to read a single byte, but reduce overall
  94    throughput.  */
  95
  96 #define LINE_SIZE_POWER (5)
  97 #define LINE_SIZE (1 << LINE_SIZE_POWER)
  98
  99 /* Each cache block holds LINE_SIZE bytes of data
 100    starting at a multiple-of-LINE_SIZE address.  */
 101
 102 #define LINE_SIZE_MASK  ((LINE_SIZE - 1))
 103 #define XFORM(x)        ((x) & LINE_SIZE_MASK)
 104 #define MASK(x)         ((x) & ~LINE_SIZE_MASK)
 105
 106
 107 #define ENTRY_BAD   0           /* data at this byte is wrong */
 108 #define ENTRY_DIRTY 1           /* data at this byte needs to be written back */
 109 #define ENTRY_OK    2           /* data at this byte is same as in memory */
 110
 111
 112 struct dcache_block
 113   {
 114     struct dcache_block *p;     /* next in list */
 115     CORE_ADDR addr;             /* Address for which data is recorded.  */
 116     char data[LINE_SIZE];       /* bytes at given address */
 117     unsigned char state[LINE_SIZE];     /* what state the data is in */
 118
 119     /* whether anything in state is dirty - used to speed up the
 120        dirty scan. */
 121     int anydirty;
 122
 123     int refs;
 124   };
 125
 126
 127 struct dcache_struct
 128   {
 129     /* Function to actually read the target memory. */
 130     memxferfunc read_memory;
 131
 132     /* Function to actually write the target memory */
 133     memxferfunc write_memory;
 134
 135     /* free list */
 136     struct dcache_block *free_head;
 137     struct dcache_block *free_tail;
 138
 139     /* in use list */
 140     struct dcache_block *valid_head;
 141     struct dcache_block *valid_tail;
 142
 143     /* The cache itself. */
 144     struct dcache_block *the_cache;
 145
 146     /* potentially, if the cache was enabled, and then turned off, and
 147        then turned on again, the stuff in it could be stale, so this is
 148        used to mark it */
 149     int cache_has_stuff;
 150   };
 151
 152 static int dcache_poke_byte (DCACHE * dcache, CORE_ADDR addr, char *ptr);
 153
 154 static int dcache_peek_byte (DCACHE * dcache, CORE_ADDR addr, char *ptr);
 155
 156 static struct dcache_block *dcache_hit (DCACHE * dcache, CORE_ADDR addr);
 157
 158 static int dcache_write_line (DCACHE * dcache, struct dcache_block *db);
 159
 160 static struct dcache_block *dcache_alloc (DCACHE * dcache);
 161
 162 static int dcache_writeback (DCACHE * dcache);
 163
 164 static void dcache_info (char *exp, int tty);
 165
 166 void _initialize_dcache (void);
 167
 168 static int dcache_enabled_p = 0;
 169
 170 DCACHE *last_cache;             /* Used by info dcache */
 171
 172
 173 /* Free all the data cache blocks, thus discarding all cached data.  */
 174
 175 void
 176 dcache_flush (DCACHE *dcache)
 177 {
 178   int i;
 179   dcache->valid_head = 0;
 180   dcache->valid_tail = 0;
 181
 182   dcache->free_head = 0;
 183   dcache->free_tail = 0;
 184
 185   for (i = 0; i < DCACHE_SIZE; i++)
 186     {
 187       struct dcache_block *db = dcache->the_cache + i;
 188
 189       if (!dcache->free_head)
 190         dcache->free_head = db;
 191       else
 192         dcache->free_tail->p = db;
 193       dcache->free_tail = db;
 194       db->p = 0;
 195     }
 196
 197   dcache->cache_has_stuff = 0;
 198
 199   return;
 200 }
 201
 202 /* If addr is present in the dcache, return the address of the block
 203    containing it. */
 204
 205 static struct dcache_block *
 206 dcache_hit (DCACHE *dcache, CORE_ADDR addr)
 207 {
 208   register struct dcache_block *db;
 209
 210   /* Search all cache blocks for one that is at this address.  */
 211   db = dcache->valid_head;
 212
 213   while (db)
 214     {
 215       if (MASK (addr) == db->addr)
 216         {
 217           db->refs++;
 218           return db;
 219         }
 220       db = db->p;
 221     }
 222
 223   return NULL;
 224 }
 225
 226 /* Make sure that anything in this line which needs to
 227    be written is. */
 228
 229 static int
 230 dcache_write_line (DCACHE *dcache, register struct dcache_block *db)
 231 {
 232   int s;
 233   int e;
 234   s = 0;
 235   if (db->anydirty)
 236     {
 237       for (s = 0; s < LINE_SIZE; s++)
 238         {
 239           if (db->state[s] == ENTRY_DIRTY)
 240             {
 241               int len = 0;
 242               for (e = s; e < LINE_SIZE; e++, len++)
 243                 if (db->state[e] != ENTRY_DIRTY)
 244                   break;
 245               {
 246                 /* all bytes from s..s+len-1 need to
 247                    be written out */
 248                 int done = 0;
 249                 while (done < len)
 250                   {
 251                     int t = dcache->write_memory (db->addr + s + done,
 252                                                   db->data + s + done,
 253                                                   len - done);
 254                     if (t == 0)
 255                       return 0;
 256                     done += t;
 257                   }
 258                 memset (db->state + s, ENTRY_OK, len);
 259                 s = e;
 260               }
 261             }
 262         }
 263       db->anydirty = 0;
 264     }
 265   return 1;
 266 }
 267
 268
 269 /* Get a free cache block, put or keep it on the valid list,
 270    and return its address.  The caller should store into the block
 271    the address and data that it describes, then remque it from the
 272    free list and insert it into the valid list.  This procedure
 273    prevents errors from creeping in if a memory retrieval is
 274    interrupted (which used to put garbage blocks in the valid
 275    list...).  */
 276
 277 static struct dcache_block *
 278 dcache_alloc (DCACHE *dcache)
 279 {
 280   register struct dcache_block *db;
 281
 282   if (dcache_enabled_p == 0)
 283     abort ();
 284
 285   /* Take something from the free list */
 286   db = dcache->free_head;
 287   if (db)
 288     {
 289       dcache->free_head = db->p;
 290     }
 291   else
 292     {
 293       /* Nothing left on free list, so grab one from the valid list */
 294       db = dcache->valid_head;
 295       dcache->valid_head = db->p;
 296
 297       dcache_write_line (dcache, db);
 298     }
 299
 300   /* append this line to end of valid list */
 301   if (!dcache->valid_head)
 302     dcache->valid_head = db;
 303   else
 304     dcache->valid_tail->p = db;
 305   dcache->valid_tail = db;
 306   db->p = 0;
 307
 308   return db;
 309 }
 310
 311 /* Using the data cache DCACHE return the contents of the byte at
 312    address ADDR in the remote machine.
 313
 314    Returns 0 on error. */
 315
 316 static int
 317 dcache_peek_byte (DCACHE *dcache, CORE_ADDR addr, char *ptr)
 318 {
 319   register struct dcache_block *db = dcache_hit (dcache, addr);
 320   int ok = 1;
 321   int done = 0;
 322   if (db == 0
 323       || db->state[XFORM (addr)] == ENTRY_BAD)
 324     {
 325       if (db)
 326         {
 327           dcache_write_line (dcache, db);
 328         }
 329       else
 330         db = dcache_alloc (dcache);
 331       immediate_quit++;
 332       db->addr = MASK (addr);
 333       while (done < LINE_SIZE)
 334         {
 335           int try =
 336           (*dcache->read_memory)
 337           (db->addr + done,
 338            db->data + done,
 339            LINE_SIZE - done);
 340           if (try == 0)
 341             return 0;
 342           done += try;
 343         }
 344       immediate_quit--;
 345
 346       memset (db->state, ENTRY_OK, sizeof (db->data));
 347       db->anydirty = 0;
 348     }
 349   *ptr = db->data[XFORM (addr)];
 350   return ok;
 351 }
 352
 353 /* Writeback any dirty lines to the remote. */
 354 static int
 355 dcache_writeback (DCACHE *dcache)
 356 {
 357   struct dcache_block *db;
 358
 359   db = dcache->valid_head;
 360
 361   while (db)
 362     {
 363       if (!dcache_write_line (dcache, db))
 364         return 0;
 365       db = db->p;
 366     }
 367   return 1;
 368 }
 369
 370
 371 /* Write the byte at PTR into ADDR in the data cache.
 372    Return zero on write error.
 373  */
 374
 375 static int
 376 dcache_poke_byte (DCACHE *dcache, CORE_ADDR addr, char *ptr)
 377 {
 378   register struct dcache_block *db = dcache_hit (dcache, addr);
 379
 380   if (!db)
 381     {
 382       db = dcache_alloc (dcache);
 383       db->addr = MASK (addr);
 384       memset (db->state, ENTRY_BAD, sizeof (db->data));
 385     }
 386
 387   db->data[XFORM (addr)] = *ptr;
 388   db->state[XFORM (addr)] = ENTRY_DIRTY;
 389   db->anydirty = 1;
 390   return 1;
 391 }
 392
 393 /* Initialize the data cache.  */
 394 DCACHE *
 395 dcache_init (memxferfunc reading, memxferfunc writing)
 396 {
 397   int csize = sizeof (struct dcache_block) * DCACHE_SIZE;
 398   DCACHE *dcache;
 399
 400   dcache = (DCACHE *) xmalloc (sizeof (*dcache));
 401   dcache->read_memory = reading;
 402   dcache->write_memory = writing;
 403
 404   dcache->the_cache = (struct dcache_block *) xmalloc (csize);
 405   memset (dcache->the_cache, 0, csize);
 406
 407   dcache_flush (dcache);
 408
 409   last_cache = dcache;
 410   return dcache;
 411 }
 412
 413 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
 414    to or from debugger address MYADDR.  Write to inferior if SHOULD_WRITE is
 415    nonzero.
 416
 417    Returns length of data written or read; 0 for error.
 418
 419    This routine is indended to be called by remote_xfer_ functions. */
 420
 421 int
 422 dcache_xfer_memory (DCACHE *dcache, CORE_ADDR memaddr, char *myaddr, int len,
 423                     int should_write)
 424 {
 425   int i;
 426
 427   if (dcache_enabled_p)
 428     {
 429       int (*xfunc) (DCACHE * dcache, CORE_ADDR addr, char *ptr);
 430       xfunc = should_write ? dcache_poke_byte : dcache_peek_byte;
 431
 432       for (i = 0; i < len; i++)
 433         {
 434           if (!xfunc (dcache, memaddr + i, myaddr + i))
 435             return 0;
 436         }
 437       dcache->cache_has_stuff = 1;
 438       dcache_writeback (dcache);
 439     }
 440   else
 441     {
 442       memxferfunc xfunc;
 443       xfunc = should_write ? dcache->write_memory : dcache->read_memory;
 444
 445       if (dcache->cache_has_stuff)
 446         dcache_flush (dcache);
 447
 448       len = xfunc (memaddr, myaddr, len);
 449     }
 450   return len;
 451 }
 452
 453 static void
 454 dcache_info (char *exp, int tty)
 455 {
 456   struct dcache_block *p;
 457
 458   if (!dcache_enabled_p)
 459     {
 460       printf_filtered ("Dcache not enabled\n");
 461       return;
 462     }
 463   printf_filtered ("Dcache enabled, line width %d, depth %d\n",
 464                    LINE_SIZE, DCACHE_SIZE);
 465
 466   printf_filtered ("Cache state:\n");
 467
 468   for (p = last_cache->valid_head; p; p = p->p)
 469     {
 470       int j;
 471       printf_filtered ("Line at %s, referenced %d times\n",
 472                        paddr (p->addr), p->refs);
 473
 474       for (j = 0; j < LINE_SIZE; j++)
 475         printf_filtered ("%02x", p->data[j] & 0xFF);
 476       printf_filtered ("\n");
 477
 478       for (j = 0; j < LINE_SIZE; j++)
 479         printf_filtered (" %2x", p->state[j]);
 480       printf_filtered ("\n");
 481     }
 482 }
 483
 484 /* Turn dcache on or off. */
 485 void
 486 set_dcache_state (int what)
 487 {
 488   dcache_enabled_p = !!what;
 489 }
 490
 491 void
 492 _initialize_dcache (void)
 493 {
 494   add_show_from_set
 495     (add_set_cmd ("remotecache", class_support, var_boolean,
 496                   (char *) &dcache_enabled_p,
 497                   "\
 498 Set cache use for remote targets.\n\
 499 When on, use data caching for remote targets.  For many remote targets\n\
 500 this option can offer better throughput for reading target memory.\n\
 501 Unfortunately, gdb does not currently know anything about volatile\n\
 502 registers and thus data caching will produce incorrect results with\n\
 503 volatile registers are in use.  By default, this option is off.",
 504                   &setlist),
 505      &showlist);
 506
 507   add_info ("dcache", dcache_info,
 508             "Print information on the dcache performance.");
 509
 510 }