/* Caching code. Typically used by remote back ends for caching remote memory. Copyright 1992, 1993, 1995 Free Software Foundation, Inc. This file is part of GDB. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ #include "defs.h" #include "dcache.h" #include "gdbcmd.h" #include /* The data cache could lead to incorrect results because it doesn't know about volatile variables, thus making it impossible to debug functions which use memory mapped I/O devices. set remotecache 0 In those cases. In general the dcache speeds up performance, some speed improvement comes from the actual caching mechanism, but the major gain is in the reduction of the remote protocol overhead; instead of reading or writing a large area of memory in 4 byte requests, the cache bundles up the requests into 32 byte (actually LINE_SIZE) chunks. Reducing the overhead to an eighth of what it was. This is very obvious when displaying a large amount of data, eg, x/200x 0 caching | no yes ---------------------------- first time | 4 sec 2 sec improvement due to chunking second time | 4 sec 0 sec improvement due to caching The cache structure is unusual, we keep a number of cache blocks (DCACHE_SIZE) and each one caches a LINE_SIZEed area of memory. Within each line we remember the address of the line (always a multiple of the LINE_SIZE) and a vector of bytes over the range. There's another vector which contains the state of the bytes. ENTRY_BAD means that the byte is just plain wrong, and has no correspondence with anything else (as it would when the cache is turned on, but nothing has been done to it. ENTRY_DIRTY means that the byte has some data in it which should be written out to the remote target one day, but contains correct data. ENTRY_OK means that the data is the same in the cache as it is in remote memory. The ENTRY_DIRTY state is necessary because GDB likes to write large lumps of memory in small bits. If the caching mechanism didn't maintain the DIRTY information, then something like a two byte write would mean that the entire cache line would have to be read, the two bytes modified and then written out again. The alternative would be to not read in the cache line in the first place, and just write the two bytes directly into target memory. The trouble with that is that it really nails performance, because of the remote protocol overhead. This way, all those little writes are bundled up into an entire cache line write in one go, without having to read the cache line in the first place. */ /* This value regulates the number of cache blocks stored. Smaller values reduce the time spent searching for a cache line, and reduce memory requirements, but increase the risk of a line not being in memory */ #define DCACHE_SIZE 64 /* This value regulates the size of a cache line. Smaller values reduce the time taken to read a single byte, but reduce overall throughput. */ #define LINE_SIZE_POWER (5) #define LINE_SIZE (1 << LINE_SIZE_POWER) /* Each cache block holds LINE_SIZE bytes of data starting at a multiple-of-LINE_SIZE address. */ #define LINE_SIZE_MASK ((LINE_SIZE - 1)) #define XFORM(x) ((x) & LINE_SIZE_MASK) #define MASK(x) ((x) & ~LINE_SIZE_MASK) #define ENTRY_BAD 0 /* data at this byte is wrong */ #define ENTRY_DIRTY 1 /* data at this byte needs to be written back */ #define ENTRY_OK 2 /* data at this byte is same as in memory */ struct dcache_block { struct dcache_block *p; /* next in list */ unsigned int addr; /* Address for which data is recorded. */ char data[LINE_SIZE]; /* bytes at given address */ unsigned char state[LINE_SIZE]; /* what state the data is in */ /* whether anything in state is dirty - used to speed up the dirty scan. */ int anydirty; int refs; }; struct dcache_struct { /* Function to actually read the target memory. */ memxferfunc read_memory; /* Function to actually write the target memory */ memxferfunc write_memory; /* free list */ struct dcache_block *free_head; struct dcache_block *free_tail; /* in use list */ struct dcache_block *valid_head; struct dcache_block *valid_tail; /* The cache itself. */ struct dcache_block *the_cache; /* potentially, if the cache was enabled, and then turned off, and then turned on again, the stuff in it could be stale, so this is used to mark it */ int cache_has_stuff; } ; int remote_dcache = 1; DCACHE *last_cache; /* Used by info dcache */ /* Free all the data cache blocks, thus discarding all cached data. */ void dcache_flush (dcache) DCACHE *dcache; { int i; dcache->valid_head = 0; dcache->valid_tail = 0; dcache->free_head = 0; dcache->free_tail = 0; for (i = 0; i < DCACHE_SIZE; i++) { struct dcache_block *db = dcache->the_cache + i; if (!dcache->free_head) dcache->free_head = db; else dcache->free_tail->p = db; dcache->free_tail = db; db->p = 0; } dcache->cache_has_stuff = 0; return; } /* If addr is present in the dcache, return the address of the block containing it. */ static struct dcache_block * dcache_hit (dcache, addr) DCACHE *dcache; unsigned int addr; { register struct dcache_block *db; /* Search all cache blocks for one that is at this address. */ db = dcache->valid_head; while (db) { if (MASK(addr) == db->addr) { db->refs++; return db; } db = db->p; } return NULL; } /* Make sure that anything in this line which needs to be written is. */ static int dcache_write_line (dcache, db) DCACHE *dcache; register struct dcache_block *db; { int s; int e; s = 0; if (db->anydirty) { for (s = 0; s < LINE_SIZE; s++) { if (db->state[s] == ENTRY_DIRTY) { int len = 0; for (e = s ; e < LINE_SIZE; e++, len++) if (db->state[e] != ENTRY_DIRTY) { /* all bytes from s..s+len-1 need to be written out */ int done = 0; while (done < len) { int t = dcache->write_memory (db->addr + s + done, db->data + s + done, len - done); if (t == 0) return 0; done += t; } memset (db->state + s, ENTRY_OK, len); s = e; break; } } } db->anydirty = 0; } return 1; } /* Get a free cache block, put or keep it on the valid list, and return its address. The caller should store into the block the address and data that it describes, then remque it from the free list and insert it into the valid list. This procedure prevents errors from creeping in if a memory retrieval is interrupted (which used to put garbage blocks in the valid list...). */ static struct dcache_block * dcache_alloc (dcache) DCACHE *dcache; { register struct dcache_block *db; if (remote_dcache == 0) abort (); /* Take something from the free list */ db = dcache->free_head; if (db) { dcache->free_head = db->p; } else { /* Nothing left on free list, so grab one from the valid list */ db = dcache->valid_head; dcache->valid_head = db->p; dcache_write_line (dcache, db); } /* append this line to end of valid list */ if (!dcache->valid_head) dcache->valid_head = db; else dcache->valid_tail->p = db; dcache->valid_tail = db; db->p = 0; return db; } /* Using the data cache DCACHE return the contents of the byte at address ADDR in the remote machine. Returns 0 on error. */ int dcache_peek_byte (dcache, addr, ptr) DCACHE *dcache; CORE_ADDR addr; char *ptr; { register struct dcache_block *db = dcache_hit (dcache, addr); int ok=1; int done = 0; if (db == 0 || db->state[XFORM (addr)] == ENTRY_BAD) { if (db) { dcache_write_line (dcache, db); } else db = dcache_alloc (dcache); immediate_quit++; db->addr = MASK (addr); while (done < LINE_SIZE) { int try = (*dcache->read_memory) (db->addr + done, db->data + done, LINE_SIZE - done); if (try == 0) return 0; done += try; } immediate_quit--; memset (db->state, ENTRY_OK, sizeof (db->data)); db->anydirty = 0; } *ptr = db->data[XFORM (addr)]; return ok; } /* Using the data cache DCACHE return the contents of the word at address ADDR in the remote machine. Returns 0 on error. */ int dcache_peek (dcache, addr, data) DCACHE *dcache; CORE_ADDR addr; int *data; { char *dp = (char *) data; int i; for (i = 0; i < sizeof (int); i++) { if (!dcache_peek_byte (dcache, addr, dp + i)) return 0; } return 1; } /* Writeback any dirty lines to the remote. */ static int dcache_writeback (dcache) DCACHE *dcache; { struct dcache_block *db; db = dcache->valid_head; while (db) { if (!dcache_write_line (dcache, db)) return 0; db = db->p; } return 1; } /* Using the data cache DCACHE return the contents of the word at address ADDR in the remote machine. */ int dcache_fetch (dcache, addr) DCACHE *dcache; CORE_ADDR addr; { int res; dcache_peek (dcache, addr, &res); return res; } /* Write the byte at PTR into ADDR in the data cache. Return zero on write error. */ int dcache_poke_byte (dcache, addr, ptr) DCACHE *dcache; CORE_ADDR addr; char *ptr; { register struct dcache_block *db = dcache_hit (dcache, addr); if (!db) { db = dcache_alloc (dcache); db->addr = MASK (addr); memset (db->state, ENTRY_BAD, sizeof (db->data)); } db->data[XFORM (addr)] = *ptr; db->state[XFORM (addr)] = ENTRY_DIRTY; db->anydirty = 1; return 1; } /* Write the word at ADDR both in the data cache and in the remote machine. Return zero on write error. */ int dcache_poke (dcache, addr, data) DCACHE *dcache; CORE_ADDR addr; int data; { char *dp = (char *) (&data); int i; for (i = 0; i < sizeof (int); i++) { if (!dcache_poke_byte (dcache, addr, dp + i)) return 0; } dcache_writeback (dcache); return 1; } /* Initialize the data cache. */ DCACHE * dcache_init (reading, writing) memxferfunc reading; memxferfunc writing; { int csize = sizeof (struct dcache_block) * DCACHE_SIZE; DCACHE *dcache; dcache = (DCACHE *) xmalloc (sizeof (*dcache)); dcache->read_memory = reading; dcache->write_memory = writing; dcache->the_cache = (struct dcache_block *) xmalloc (csize); memset (dcache->the_cache, 0, csize); dcache_flush (dcache); last_cache = dcache; return dcache; } /* Read or write LEN bytes from inferior memory at MEMADDR, transferring to or from debugger address MYADDR. Write to inferior if SHOULD_WRITE is nonzero. Returns length of data written or read; 0 for error. This routine is indended to be called by remote_xfer_ functions. */ int dcache_xfer_memory (dcache, memaddr, myaddr, len, should_write) DCACHE *dcache; CORE_ADDR memaddr; char *myaddr; int len; int should_write; { int i; if (remote_dcache) { int (*xfunc) () = should_write ? dcache_poke_byte : dcache_peek_byte; for (i = 0; i < len; i++) { if (!xfunc (dcache, memaddr + i, myaddr + i)) return 0; } dcache->cache_has_stuff = 1; dcache_writeback (dcache); } else { int (*xfunc) () = should_write ? dcache->write_memory : dcache->read_memory; if (dcache->cache_has_stuff) dcache_flush (dcache); len = xfunc (memaddr, myaddr, len); } return len; } static void dcache_info (exp, tty) char *exp; int tty; { struct dcache_block *p; if (!remote_dcache) { printf_filtered ("Dcache not enabled\n"); return; } printf_filtered ("Dcache enabled, line width %d, depth %d\n", LINE_SIZE, DCACHE_SIZE); printf_filtered ("Cache state:\n"); for (p = last_cache->valid_head; p; p = p->p) { int j; printf_filtered ("Line at %08xd, referenced %d times\n", p->addr, p->refs); for (j = 0; j < LINE_SIZE; j++) printf_filtered ("%02x", p->data[j] & 0xFF); printf_filtered ("\n"); for (j = 0; j < LINE_SIZE; j++) printf_filtered (" %2x", p->state[j]); printf_filtered ("\n"); } } void _initialize_dcache () { add_show_from_set (add_set_cmd ("remotecache", class_support, var_boolean, (char *) &remote_dcache, "\ Set cache use for remote targets.\n\ When on, use data caching for remote targets. For many remote targets\n\ this option can offer better throughput for reading target memory.\n\ Unfortunately, gdb does not currently know anything about volatile\n\ registers and thus data caching will produce incorrect results with\n\ volatile registers are in use. By default, this option is on.", &setlist), &showlist); add_info ("dcache", dcache_info, "Print information on the dcache performance."); }