1 /* Caching code. Typically used by remote back ends for
4 Copyright 1992-1993, 1995, 1998-1999 Free Software Foundation, Inc.
6 This file is part of GDB.
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.
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.
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. */
26 #include "gdb_string.h"
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.
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,
49 ----------------------------
50 first time | 4 sec 2 sec improvement due to chunking
51 second time | 4 sec 0 sec improvement due to caching
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.
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.
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
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.
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 */
90 #define DCACHE_SIZE 64
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
96 #define LINE_SIZE_POWER (5)
97 #define LINE_SIZE (1 << LINE_SIZE_POWER)
99 /* Each cache block holds LINE_SIZE bytes of data
100 starting at a multiple-of-LINE_SIZE address. */
102 #define LINE_SIZE_MASK ((LINE_SIZE - 1))
103 #define XFORM(x) ((x) & LINE_SIZE_MASK)
104 #define MASK(x) ((x) & ~LINE_SIZE_MASK)
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 */
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 */
119 /* whether anything in state is dirty - used to speed up the
129 /* Function to actually read the target memory. */
130 memxferfunc read_memory
;
132 /* Function to actually write the target memory */
133 memxferfunc write_memory
;
136 struct dcache_block
*free_head
;
137 struct dcache_block
*free_tail
;
140 struct dcache_block
*valid_head
;
141 struct dcache_block
*valid_tail
;
143 /* The cache itself. */
144 struct dcache_block
*the_cache
;
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
152 static int dcache_poke_byte (DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
);
154 static int dcache_peek_byte (DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
);
156 static struct dcache_block
*dcache_hit (DCACHE
*dcache
, CORE_ADDR addr
);
158 static int dcache_write_line (DCACHE
*dcache
, struct dcache_block
*db
);
160 static int dcache_read_line (DCACHE
*dcache
, struct dcache_block
*db
);
162 static struct dcache_block
*dcache_alloc (DCACHE
*dcache
, CORE_ADDR addr
);
164 static int dcache_writeback (DCACHE
*dcache
);
166 static void dcache_info (char *exp
, int tty
);
168 void _initialize_dcache (void);
170 static int dcache_enabled_p
= 0;
172 DCACHE
*last_cache
; /* Used by info dcache */
175 /* Free all the data cache blocks, thus discarding all cached data. */
178 dcache_invd (DCACHE
*dcache
)
181 dcache
->valid_head
= 0;
182 dcache
->valid_tail
= 0;
184 dcache
->free_head
= 0;
185 dcache
->free_tail
= 0;
187 for (i
= 0; i
< DCACHE_SIZE
; i
++)
189 struct dcache_block
*db
= dcache
->the_cache
+ i
;
191 if (!dcache
->free_head
)
192 dcache
->free_head
= db
;
194 dcache
->free_tail
->p
= db
;
195 dcache
->free_tail
= db
;
199 dcache
->cache_has_stuff
= 0;
204 /* If addr is present in the dcache, return the address of the block
207 static struct dcache_block
*
208 dcache_hit (DCACHE
*dcache
, CORE_ADDR addr
)
210 register struct dcache_block
*db
;
212 /* Search all cache blocks for one that is at this address. */
213 db
= dcache
->valid_head
;
217 if (MASK (addr
) == db
->addr
)
228 /* Make sure that anything in this line which needs to
232 dcache_write_line (DCACHE
*dcache
, register struct dcache_block
*db
)
239 for (s
= 0; s
< LINE_SIZE
; s
++)
241 if (db
->state
[s
] == ENTRY_DIRTY
)
244 for (e
= s
; e
< LINE_SIZE
; e
++, len
++)
245 if (db
->state
[e
] != ENTRY_DIRTY
)
248 /* all bytes from s..s+len-1 need to
253 int t
= dcache
->write_memory (db
->addr
+ s
+ done
,
260 memset (db
->state
+ s
, ENTRY_OK
, len
);
271 /* Read cache line */
273 dcache_read_line (DCACHE
*dcache
, struct dcache_block
*db
)
280 /* If there are any dirty bytes in the line, it must be written
281 before a new line can be read */
284 if (!dcache_write_line (dcache
, db
))
294 res
= (*dcache
->read_memory
) (memaddr
, myaddr
, len
);
303 memset (db
->state
, ENTRY_OK
, sizeof (db
->data
));
309 /* Get a free cache block, put or keep it on the valid list,
310 and return its address. */
312 static struct dcache_block
*
313 dcache_alloc (DCACHE
*dcache
, CORE_ADDR addr
)
315 register struct dcache_block
*db
;
317 if (dcache_enabled_p
== 0)
320 /* Take something from the free list */
321 db
= dcache
->free_head
;
324 dcache
->free_head
= db
->p
;
328 /* Nothing left on free list, so grab one from the valid list */
329 db
= dcache
->valid_head
;
331 if (!dcache_write_line (dcache
, db
))
334 dcache
->valid_head
= db
->p
;
337 db
->addr
= MASK(addr
);
340 memset (db
->state
, ENTRY_BAD
, sizeof (db
->data
));
342 /* append this line to end of valid list */
343 if (!dcache
->valid_head
)
344 dcache
->valid_head
= db
;
346 dcache
->valid_tail
->p
= db
;
347 dcache
->valid_tail
= db
;
353 /* Writeback any dirty lines to the remote. */
355 dcache_writeback (DCACHE
*dcache
)
357 struct dcache_block
*db
;
359 db
= dcache
->valid_head
;
363 if (!dcache_write_line (dcache
, db
))
371 /* Using the data cache DCACHE return the contents of the byte at
372 address ADDR in the remote machine.
374 Returns 0 on error. */
377 dcache_peek_byte (DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
)
379 register struct dcache_block
*db
= dcache_hit (dcache
, addr
);
383 db
= dcache_alloc (dcache
, addr
);
388 if (db
->state
[XFORM (addr
)] == ENTRY_BAD
)
390 if (!dcache_read_line(dcache
, db
))
394 *ptr
= db
->data
[XFORM (addr
)];
399 /* Write the byte at PTR into ADDR in the data cache.
400 Return zero on write error.
404 dcache_poke_byte (DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
)
406 register struct dcache_block
*db
= dcache_hit (dcache
, addr
);
410 db
= dcache_alloc (dcache
, addr
);
415 db
->data
[XFORM (addr
)] = *ptr
;
416 db
->state
[XFORM (addr
)] = ENTRY_DIRTY
;
421 /* Initialize the data cache. */
423 dcache_init (memxferfunc reading
, memxferfunc writing
)
425 int csize
= sizeof (struct dcache_block
) * DCACHE_SIZE
;
428 dcache
= (DCACHE
*) xmalloc (sizeof (*dcache
));
429 dcache
->read_memory
= reading
;
430 dcache
->write_memory
= writing
;
432 dcache
->the_cache
= (struct dcache_block
*) xmalloc (csize
);
433 memset (dcache
->the_cache
, 0, csize
);
435 dcache_invd (dcache
);
441 /* Free a data cache */
443 dcache_free (DCACHE
*dcache
)
445 if (last_cache
== dcache
)
448 free (dcache
->the_cache
);
452 /* Read or write LEN bytes from inferior memory at MEMADDR, transferring
453 to or from debugger address MYADDR. Write to inferior if SHOULD_WRITE is
456 Returns length of data written or read; 0 for error.
458 This routine is indended to be called by remote_xfer_ functions. */
461 dcache_xfer_memory (DCACHE
*dcache
, CORE_ADDR memaddr
, char *myaddr
, int len
,
466 if (dcache_enabled_p
)
468 int (*xfunc
) (DCACHE
*dcache
, CORE_ADDR addr
, char *ptr
);
469 xfunc
= should_write
? dcache_poke_byte
: dcache_peek_byte
;
471 for (i
= 0; i
< len
; i
++)
473 if (!xfunc (dcache
, memaddr
+ i
, myaddr
+ i
))
478 dcache_writeback (dcache
);
480 dcache
->cache_has_stuff
= 1;
485 xfunc
= should_write
? dcache
->write_memory
: dcache
->read_memory
;
487 if (dcache
->cache_has_stuff
)
488 dcache_invd (dcache
);
490 len
= xfunc (memaddr
, myaddr
, len
);
496 dcache_info (char *exp
, int tty
)
498 struct dcache_block
*p
;
500 if (!dcache_enabled_p
)
502 printf_filtered ("Dcache not enabled\n");
505 printf_filtered ("Dcache enabled, line width %d, depth %d\n",
506 LINE_SIZE
, DCACHE_SIZE
);
510 printf_filtered ("Cache state:\n");
512 for (p
= last_cache
->valid_head
; p
; p
= p
->p
)
515 printf_filtered ("Line at %s, referenced %d times\n",
516 paddr (p
->addr
), p
->refs
);
518 for (j
= 0; j
< LINE_SIZE
; j
++)
519 printf_filtered ("%02x", p
->data
[j
] & 0xFF);
520 printf_filtered ("\n");
522 for (j
= 0; j
< LINE_SIZE
; j
++)
523 printf_filtered ("%2x", p
->state
[j
]);
524 printf_filtered ("\n");
529 /* Turn dcache on or off. */
531 set_dcache_state (int what
)
533 dcache_enabled_p
= !!what
;
537 _initialize_dcache (void)
540 (add_set_cmd ("remotecache", class_support
, var_boolean
,
541 (char *) &dcache_enabled_p
,
543 Set cache use for remote targets.\n\
544 When on, use data caching for remote targets. For many remote targets\n\
545 this option can offer better throughput for reading target memory.\n\
546 Unfortunately, gdb does not currently know anything about volatile\n\
547 registers and thus data caching will produce incorrect results with\n\
548 volatile registers are in use. By default, this option is off.",
552 add_info ("dcache", dcache_info
,
553 "Print information on the dcache performance.");
This page took 0.040025 seconds and 4 git commands to generate.