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Ok, the entry aging algorithm sucked; 1s time resolution is not enough for

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LRU.  Use a 31-bit counter instead.  If we decide to do heavy I/O through
the bootloader this will have to be revisited.
This commit is contained in:
Mike Smith 1998-11-02 23:50:59 +00:00
parent af1f6e0673
commit ddfd18e255
1 changed files with 16 additions and 7 deletions
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23
sys/boot/common/bcache.c
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@ -27,6 +27,7 @@ struct bcachectl
{ {
daddr_t bc_blkno; daddr_t bc_blkno;
time_t bc_stamp; time_t bc_stamp;
int bc_count;
}; };
static struct bcachectl *bcache_ctl; static struct bcachectl *bcache_ctl;
@ -35,6 +36,7 @@ static bitstr_t *bcache_miss;
static int bcache_nblks; static int bcache_nblks;
static int bcache_blksize; static int bcache_blksize;
static int bcache_hits, bcache_misses, bcache_ops, bcache_bypasses; static int bcache_hits, bcache_misses, bcache_ops, bcache_bypasses;
static int bcache_bcount;
static void bcache_insert(caddr_t buf, daddr_t blkno); static void bcache_insert(caddr_t buf, daddr_t blkno);
static int bcache_lookup(caddr_t buf, daddr_t blkno); static int bcache_lookup(caddr_t buf, daddr_t blkno);
@ -73,7 +75,7 @@ bcache_init(int nblks, size_t bsize)
/* Invalidate the cache */ /* Invalidate the cache */
for (i = 0; i < bcache_nblks; i++) for (i = 0; i < bcache_nblks; i++)
bcache_ctl[i].bc_stamp = 0; bcache_ctl[i].bc_count = -1;
return(0); return(0);
} }
@ -160,35 +162,42 @@ bcache_strategy(void *devdata, int rw, daddr_t blk, size_t size, void *buf, size
/* /*
* Insert a block into the cache. Retire the oldest block to do so, if required. * Insert a block into the cache. Retire the oldest block to do so, if required.
*
* XXX the LRU algorithm will fail after 2^31 blocks have been transferred.
*/ */
static void static void
bcache_insert(caddr_t buf, daddr_t blkno) bcache_insert(caddr_t buf, daddr_t blkno)
{ {
time_t now; time_t now;
int i, cand; int i, cand, ocount;
time(&now); time(&now);
cand = 0; /* assume the first block */
ocount = bcache_ctl[0].bc_count;
/* find the oldest block */ /* find the oldest block */
for (cand = 0, i = 1; i < bcache_nblks; i++) { for (i = 1; i < bcache_nblks; i++) {
if (bcache_ctl[i].bc_blkno == blkno) { if (bcache_ctl[i].bc_blkno == blkno) {
/* reuse old entry */ /* reuse old entry */
cand = i; cand = i;
break; break;
} }
if (bcache_ctl[i].bc_stamp < now) if (bcache_ctl[i].bc_count < ocount) {
ocount = bcache_ctl[i].bc_count;
cand = i; cand = i;
}
} }
DEBUG("insert blk %d -> %d @ %d", blkno, cand, now); DEBUG("insert blk %d -> %d @ %d # %d", blkno, cand, now, bcache_bcount);
bcopy(buf, bcache_data + (bcache_blksize * cand), bcache_blksize); bcopy(buf, bcache_data + (bcache_blksize * cand), bcache_blksize);
bcache_ctl[cand].bc_blkno = blkno; bcache_ctl[cand].bc_blkno = blkno;
bcache_ctl[cand].bc_stamp = now; bcache_ctl[cand].bc_stamp = now;
bcache_ctl[cand].bc_count = bcache_bcount++;
} }
/* /*
* Look for a block in the cache. Blocks more than BCACHE_TIMEOUT seconds old * Look for a block in the cache. Blocks more than BCACHE_TIMEOUT seconds old
* may be stale (removable media) and thus are discarded. Copy the block out * may be stale (removable media) and thus are discarded. Copy the block out
* if successful and return zero, or return nonzero on failure. * if successful and return zero, or return nonzero on failure.
*/ */
static int static int
@ -217,7 +226,7 @@ command_bcache(int argc, char *argv[])
int i; int i;
for (i = 0; i < bcache_nblks; i++) { for (i = 0; i < bcache_nblks; i++) {
printf(" %02x: %08x %04x", i, bcache_ctl[i].bc_blkno, bcache_ctl[i].bc_stamp & 0xffff); printf("%08x %04x %04x|", bcache_ctl[i].bc_blkno, bcache_ctl[i].bc_stamp & 0xffff, bcache_ctl[i].bc_count & 0xffff);
if (((i + 1) % 4) == 0) if (((i + 1) % 4) == 0)
printf("\n"); printf("\n");
} }