diff options
Diffstat (limited to 'block/qcow2-cache.c')
| -rw-r--r-- | block/qcow2-cache.c | 171 |
1 files changed, 75 insertions, 96 deletions
diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c index b1155492a3..ed92a098c4 100644 --- a/block/qcow2-cache.c +++ b/block/qcow2-cache.c @@ -28,62 +28,68 @@ #include "trace.h" typedef struct Qcow2CachedTable { - void* table; - int64_t offset; - bool dirty; - int cache_hits; - int ref; + int64_t offset; + bool dirty; + uint64_t lru_counter; + int ref; } Qcow2CachedTable; struct Qcow2Cache { - Qcow2CachedTable* entries; - struct Qcow2Cache* depends; + Qcow2CachedTable *entries; + struct Qcow2Cache *depends; int size; bool depends_on_flush; + void *table_array; + uint64_t lru_counter; }; +static inline void *qcow2_cache_get_table_addr(BlockDriverState *bs, + Qcow2Cache *c, int table) +{ + BDRVQcowState *s = bs->opaque; + return (uint8_t *) c->table_array + (size_t) table * s->cluster_size; +} + +static inline int qcow2_cache_get_table_idx(BlockDriverState *bs, + Qcow2Cache *c, void *table) +{ + BDRVQcowState *s = bs->opaque; + ptrdiff_t table_offset = (uint8_t *) table - (uint8_t *) c->table_array; + int idx = table_offset / s->cluster_size; + assert(idx >= 0 && idx < c->size && table_offset % s->cluster_size == 0); + return idx; +} + Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables) { BDRVQcowState *s = bs->opaque; Qcow2Cache *c; - int i; c = g_new0(Qcow2Cache, 1); c->size = num_tables; c->entries = g_try_new0(Qcow2CachedTable, num_tables); - if (!c->entries) { - goto fail; - } - - for (i = 0; i < c->size; i++) { - c->entries[i].table = qemu_try_blockalign(bs->file, s->cluster_size); - if (c->entries[i].table == NULL) { - goto fail; - } + c->table_array = qemu_try_blockalign(bs->file, + (size_t) num_tables * s->cluster_size); + + if (!c->entries || !c->table_array) { + qemu_vfree(c->table_array); + g_free(c->entries); + g_free(c); + c = NULL; } return c; - -fail: - if (c->entries) { - for (i = 0; i < c->size; i++) { - qemu_vfree(c->entries[i].table); - } - } - g_free(c->entries); - g_free(c); - return NULL; } -int qcow2_cache_destroy(BlockDriverState* bs, Qcow2Cache *c) +int qcow2_cache_destroy(BlockDriverState *bs, Qcow2Cache *c) { int i; for (i = 0; i < c->size; i++) { assert(c->entries[i].ref == 0); - qemu_vfree(c->entries[i].table); } + qemu_vfree(c->table_array); g_free(c->entries); g_free(c); @@ -151,8 +157,8 @@ static int qcow2_cache_entry_flush(BlockDriverState *bs, Qcow2Cache *c, int i) BLKDBG_EVENT(bs->file, BLKDBG_L2_UPDATE); } - ret = bdrv_pwrite(bs->file, c->entries[i].offset, c->entries[i].table, - s->cluster_size); + ret = bdrv_pwrite(bs->file, c->entries[i].offset, + qcow2_cache_get_table_addr(bs, c, i), s->cluster_size); if (ret < 0) { return ret; } @@ -228,42 +234,12 @@ int qcow2_cache_empty(BlockDriverState *bs, Qcow2Cache *c) for (i = 0; i < c->size; i++) { assert(c->entries[i].ref == 0); c->entries[i].offset = 0; - c->entries[i].cache_hits = 0; + c->entries[i].lru_counter = 0; } - return 0; -} - -static int qcow2_cache_find_entry_to_replace(Qcow2Cache *c) -{ - int i; - int min_count = INT_MAX; - int min_index = -1; - - - for (i = 0; i < c->size; i++) { - if (c->entries[i].ref) { - continue; - } - - if (c->entries[i].cache_hits < min_count) { - min_index = i; - min_count = c->entries[i].cache_hits; - } - - /* Give newer hits priority */ - /* TODO Check how to optimize the replacement strategy */ - if (c->entries[i].cache_hits > 1) { - c->entries[i].cache_hits /= 2; - } - } + c->lru_counter = 0; - if (min_index == -1) { - /* This can't happen in current synchronous code, but leave the check - * here as a reminder for whoever starts using AIO with the cache */ - abort(); - } - return min_index; + return 0; } static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c, @@ -272,19 +248,37 @@ static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c, BDRVQcowState *s = bs->opaque; int i; int ret; + int lookup_index; + uint64_t min_lru_counter = UINT64_MAX; + int min_lru_index = -1; trace_qcow2_cache_get(qemu_coroutine_self(), c == s->l2_table_cache, offset, read_from_disk); /* Check if the table is already cached */ - for (i = 0; i < c->size; i++) { - if (c->entries[i].offset == offset) { + i = lookup_index = (offset / s->cluster_size * 4) % c->size; + do { + const Qcow2CachedTable *t = &c->entries[i]; + if (t->offset == offset) { goto found; } + if (t->ref == 0 && t->lru_counter < min_lru_counter) { + min_lru_counter = t->lru_counter; + min_lru_index = i; + } + if (++i == c->size) { + i = 0; + } + } while (i != lookup_index); + + if (min_lru_index == -1) { + /* This can't happen in current synchronous code, but leave the check + * here as a reminder for whoever starts using AIO with the cache */ + abort(); } - /* If not, write a table back and replace it */ - i = qcow2_cache_find_entry_to_replace(c); + /* Cache miss: write a table back and replace it */ + i = min_lru_index; trace_qcow2_cache_get_replace_entry(qemu_coroutine_self(), c == s->l2_table_cache, i); if (i < 0) { @@ -304,22 +298,19 @@ static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c, BLKDBG_EVENT(bs->file, BLKDBG_L2_LOAD); } - ret = bdrv_pread(bs->file, offset, c->entries[i].table, s->cluster_size); + ret = bdrv_pread(bs->file, offset, qcow2_cache_get_table_addr(bs, c, i), + s->cluster_size); if (ret < 0) { return ret; } } - /* Give the table some hits for the start so that it won't be replaced - * immediately. The number 32 is completely arbitrary. */ - c->entries[i].cache_hits = 32; c->entries[i].offset = offset; /* And return the right table */ found: - c->entries[i].cache_hits++; c->entries[i].ref++; - *table = c->entries[i].table; + *table = qcow2_cache_get_table_addr(bs, c, i); trace_qcow2_cache_get_done(qemu_coroutine_self(), c == s->l2_table_cache, i); @@ -339,36 +330,24 @@ int qcow2_cache_get_empty(BlockDriverState *bs, Qcow2Cache *c, uint64_t offset, return qcow2_cache_do_get(bs, c, offset, table, false); } -int qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table) +void qcow2_cache_put(BlockDriverState *bs, Qcow2Cache *c, void **table) { - int i; + int i = qcow2_cache_get_table_idx(bs, c, *table); - for (i = 0; i < c->size; i++) { - if (c->entries[i].table == *table) { - goto found; - } - } - return -ENOENT; - -found: c->entries[i].ref--; *table = NULL; + if (c->entries[i].ref == 0) { + c->entries[i].lru_counter = ++c->lru_counter; + } + assert(c->entries[i].ref >= 0); - return 0; } -void qcow2_cache_entry_mark_dirty(Qcow2Cache *c, void *table) +void qcow2_cache_entry_mark_dirty(BlockDriverState *bs, Qcow2Cache *c, + void *table) { - int i; - - for (i = 0; i < c->size; i++) { - if (c->entries[i].table == table) { - goto found; - } - } - abort(); - -found: + int i = qcow2_cache_get_table_idx(bs, c, table); + assert(c->entries[i].offset != 0); c->entries[i].dirty = true; } |