diff options
| -rw-r--r-- | stand/common/bcache.c | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/stand/common/bcache.c b/stand/common/bcache.c index 0eeb7e74ee96..b3b8b22c7d21 100644 --- a/stand/common/bcache.c +++ b/stand/common/bcache.c @@ -238,17 +238,27 @@ read_strategy(void *devdata, int rw, daddr_t blk, size_t size, if (BCACHE_LOOKUP(bc, (daddr_t)(blk + i))) { bcache_misses += (nblk - i); complete = 0; - if (nblk - i > BCACHE_MINREADAHEAD && bc->ra > BCACHE_MINREADAHEAD) - bc->ra >>= 1; /* reduce read ahead */ break; } else { bcache_hits++; } } - if (complete) { /* whole set was in cache, return it */ + /* + * Adjust read-ahead size if appropriate. Subject to the requirement + * that bc->ra must stay in between MINREADAHEAD and READAHEAD, we + * increase it when we notice that readahead was useful and decrease + * it when we notice that readahead was not useful. + */ + if (complete) { if (bc->ra < BCACHE_READAHEAD) - bc->ra <<= 1; /* increase read ahead */ + bc->ra <<= 1; /* increase read ahead */ + } else { + if (nblk - i > BCACHE_MINREADAHEAD && bc->ra > BCACHE_MINREADAHEAD) + bc->ra >>= 1; /* reduce read ahead */ + } + + if (complete) { /* whole set was in cache, return it */ bcopy(bc->bcache_data + (bcache_blksize * BHASH(bc, blk)), buf, size); goto done; } |