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An advantage is achieved due to the fact that from readahead requests can become queued faster than request from Guest OS. Add pcache-readahead-size open parameter. Signed-off-by: Pavel Butsykin --- block/pcache.c | 118 ++++++++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 100 insertions(+), 18 deletions(-) diff --git a/block/pcache.c b/block/pcache.c index cb5f884..90b3f85 100644 --- a/block/pcache.c +++ b/block/pcache.c @@ -92,7 +92,10 @@ typedef struct BDRVPCacheState { ReqStor pcache; - uint32_t cfg_cache_size; + struct { + uint32_t cache_size; + uint32_t readahead_size; + } cfg; #ifdef PCACHE_DEBUG uint64_t shrink_cnt_node; @@ -134,6 +137,7 @@ static const AIOCBInfo pcache_aiocb_info = { }; #define PCACHE_OPT_CACHE_SIZE "pcache-full-size" +#define PCACHE_OPT_READAHEAD_SIZE "pcache-readahead-size" static QemuOptsList runtime_opts = { .name = "pcache", @@ -149,6 +153,11 @@ static QemuOptsList runtime_opts = { .type = QEMU_OPT_SIZE, .help = "Total cache size", }, + { + .name = PCACHE_OPT_READAHEAD_SIZE, + .type = QEMU_OPT_SIZE, + .help = "Prefetch cache readahead size", + }, { /* end of list */ } }, }; @@ -156,6 +165,7 @@ static QemuOptsList runtime_opts = { #define KB_BITS 10 #define MB_BITS 20 #define PCACHE_DEFAULT_CACHE_SIZE (4 << MB_BITS) +#define PCACHE_DEFAULT_READAHEAD_SIZE (128 << KB_BITS) enum { NODE_SUCCESS_STATUS = 0, @@ -164,13 +174,16 @@ enum { NODE_GHOST_STATUS = 3 /* only for debugging */ }; +enum { + PCACHE_AIO_READ = 1, + PCACHE_AIO_WRITE = 2, + PCACHE_AIO_READAHEAD = 4 +}; + #define PCNODE(_n) ((PCNode *)(_n)) static inline void pcache_node_unref(BDRVPCacheState *s, PCNode *node) { - assert(node->status == NODE_SUCCESS_STATUS || - node->status == NODE_REMOVE_STATUS); - if (atomic_fetch_dec(&node->ref) == 0) { assert(node->status == NODE_REMOVE_STATUS); @@ -333,7 +346,7 @@ static inline PCNode *pcache_get_most_unused_node(BDRVPCacheState *s) static void pcache_try_shrink(BDRVPCacheState *s) { - while (s->pcache.curr_size > s->cfg_cache_size) { + while (s->pcache.curr_size > s->cfg.cache_size) { PCNode *rmv_node; /* it can happen if all nodes are waiting */ if (QTAILQ_EMPTY(&s->pcache.lru.list)) { @@ -626,7 +639,9 @@ static void pcache_merge_requests(PrefCacheAIOCB *acb) pcache_node_submit(req); - pcache_node_read_buf(acb, node); + if (!(acb->aio_type & PCACHE_AIO_READAHEAD)) { + pcache_node_read_buf(acb, node); + } pcache_complete_acb_wait_queue(acb->s, node); @@ -668,12 +683,16 @@ static void pcache_aio_cb(void *opaque, int ret) { PrefCacheAIOCB *acb = opaque; - if (acb->aio_type & QEMU_AIO_READ) { + if (acb->aio_type & PCACHE_AIO_READ) { if (atomic_dec_fetch(&acb->requests.cnt) > 0) { return; } pcache_merge_requests(acb); - } else { /* QEMU_AIO_WRITE */ + if (acb->aio_type & PCACHE_AIO_READAHEAD) { + qemu_aio_unref(acb); + return; + } + } else { /* PCACHE_AIO_WRITE */ pcache_try_node_drop(acb); /* XXX: use write through */ } @@ -702,6 +721,69 @@ static PrefCacheAIOCB *pcache_aio_get(BlockDriverState *bs, int64_t sector_num, return acb; } +static void pcache_send_acb_request_list(BlockDriverState *bs, + PrefCacheAIOCB *acb) +{ + PrefCachePartReq *req; + + assert(acb->requests.cnt != 0); + qemu_co_mutex_lock(&acb->requests.lock); + QTAILQ_FOREACH(req, &acb->requests.list, entry) { + bdrv_aio_readv(bs->file, req->sector_num, &req->qiov, + req->nb_sectors, pcache_aio_cb, acb); + } + qemu_co_mutex_unlock(&acb->requests.lock); +} + +static bool check_allocated_blocks(BlockDriverState *bs, int64_t sector_num, + int32_t nb_sectors) +{ + int ret, num; + + do { + ret = bdrv_is_allocated(bs, sector_num, nb_sectors, &num); + if (ret <= 0) { + return false; + } + sector_num += num; + nb_sectors -= num; + + } while (nb_sectors); + + return true; +} + +static void pcache_readahead_request(BlockDriverState *bs, PrefCacheAIOCB *acb) +{ + BDRVPCacheState *s = acb->s; + PrefCacheAIOCB *acb_readahead; + RbNodeKey key; + uint64_t total_sectors = bdrv_nb_sectors(bs); + PCNode *node = NULL; + + prefetch_init_key(acb, &key); + + key.num = key.num + key.size; + if (total_sectors <= key.num + s->cfg.readahead_size) { + return; /* readahead too small or beyond end of disk */ + } + key.size = s->cfg.readahead_size; + + if (!check_allocated_blocks(bs->file->bs, key.num, key.size)) { + return; + } + + acb_readahead = pcache_aio_get(bs, key.num, NULL, key.size, acb->common.cb, + acb->common.opaque, PCACHE_AIO_READ | + PCACHE_AIO_READAHEAD); + if (!pcache_node_find_and_create(acb_readahead, &key, &node)) { + pcache_node_unref(s, node); + qemu_aio_unref(acb_readahead); + return; + } + pcache_send_acb_request_list(bs, acb_readahead); +} + static BlockAIOCB *pcache_aio_readv(BlockDriverState *bs, int64_t sector_num, QEMUIOVector *qiov, @@ -710,22 +792,18 @@ static BlockAIOCB *pcache_aio_readv(BlockDriverState *bs, void *opaque) { PrefCacheAIOCB *acb = pcache_aio_get(bs, sector_num, qiov, nb_sectors, cb, - opaque, QEMU_AIO_READ); + opaque, PCACHE_AIO_READ); int32_t status = pcache_prefetch(acb); if (status == PREFETCH_FULL_UP) { assert(acb->requests.cnt == 0); complete_aio_request(acb); } else { - PrefCachePartReq *req; assert(acb->requests.cnt != 0); - qemu_co_mutex_lock(&acb->requests.lock); - QTAILQ_FOREACH(req, &acb->requests.list, entry) { - bdrv_aio_readv(bs->file, req->sector_num, &req->qiov, - req->nb_sectors, pcache_aio_cb, acb); - } - qemu_co_mutex_unlock(&acb->requests.lock); + pcache_send_acb_request_list(bs, acb); } + pcache_readahead_request(bs, acb); + return &acb->common; } @@ -737,7 +815,7 @@ static BlockAIOCB *pcache_aio_writev(BlockDriverState *bs, void *opaque) { PrefCacheAIOCB *acb = pcache_aio_get(bs, sector_num, qiov, nb_sectors, cb, - opaque, QEMU_AIO_WRITE); + opaque, PCACHE_AIO_WRITE); bdrv_aio_writev(bs->file, sector_num, qiov, nb_sectors, pcache_aio_cb, acb); @@ -748,8 +826,11 @@ static void pcache_state_init(QemuOpts *opts, BDRVPCacheState *s) { uint64_t cache_size = qemu_opt_get_size(opts, PCACHE_OPT_CACHE_SIZE, PCACHE_DEFAULT_CACHE_SIZE); + uint64_t readahead_size = qemu_opt_get_size(opts, PCACHE_OPT_READAHEAD_SIZE, + PCACHE_DEFAULT_READAHEAD_SIZE); DPRINTF("pcache configure:\n"); DPRINTF("pcache-full-size = %jd\n", cache_size); + DPRINTF("readahead_size = %jd\n", readahead_size); s->pcache.tree.root = RB_ROOT; qemu_co_mutex_init(&s->pcache.tree.lock); @@ -757,7 +838,8 @@ static void pcache_state_init(QemuOpts *opts, BDRVPCacheState *s) qemu_co_mutex_init(&s->pcache.lru.lock); s->pcache.curr_size = 0; - s->cfg_cache_size = cache_size >> BDRV_SECTOR_BITS; + s->cfg.cache_size = cache_size >> BDRV_SECTOR_BITS; + s->cfg.readahead_size = readahead_size >> BDRV_SECTOR_BITS; #ifdef PCACHE_DEBUG QTAILQ_INIT(&s->death_node_list);