[Qemu-block] [PATCH RFC v2 18/22] block/pcache: add pcache skip large aio read

[Pavel Butsykin]

This change will allow more efficient use of cache memory and
filter the case for which the pcache isn't efficient.  We miss requests
that are not required in the optimization and thereby reducing the number
of unnecessary readaheads.

Add pcache-max-aio-size open parameter.

Signed-off-by: Pavel Butsykin <address@hidden>
---
 block/pcache.c | 49 ++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 40 insertions(+), 9 deletions(-)

diff --git a/block/pcache.c b/block/pcache.c
index 7a317fc..287156a 100644
--- a/block/pcache.c
+++ b/block/pcache.c
@@ -100,6 +100,7 @@ typedef struct BDRVPCacheState {
     struct {
         uint32_t cache_size;
         uint32_t readahead_size;
+        uint32_t max_aio_size;
         uint32_t lreq_pool_size;
     } cfg;
 
@@ -144,6 +145,7 @@ static const AIOCBInfo pcache_aiocb_info = {
 
 #define PCACHE_OPT_CACHE_SIZE "pcache-full-size"
 #define PCACHE_OPT_READAHEAD_SIZE "pcache-readahead-size"
+#define PCACHE_OPT_MAX_AIO_SIZE "pcache-max-aio-size"
 
 static QemuOptsList runtime_opts = {
     .name = "pcache",
@@ -164,6 +166,11 @@ static QemuOptsList runtime_opts = {
             .type = QEMU_OPT_SIZE,
             .help = "Prefetch cache readahead size",
         },
+        {
+            .name = PCACHE_OPT_MAX_AIO_SIZE,
+            .type = QEMU_OPT_SIZE,
+            .help = "Maximum size of aio which is handled by pcache",
+        },
         { /* end of list */ }
     },
 };
@@ -173,6 +180,7 @@ static QemuOptsList runtime_opts = {
 #define PCACHE_DEFAULT_CACHE_SIZE (4 << MB_BITS)
 #define PCACHE_DEFAULT_READAHEAD_SIZE (128 << KB_BITS)
 #define PCACHE_DEFAULT_POOL_STAT_SIZE (1 << MB_BITS)
+#define PCACHE_DEFAULT_MAX_AIO_SIZE (32 << KB_BITS)
 
 enum {
     NODE_SUCCESS_STATUS = 0,
@@ -386,12 +394,7 @@ static void lreq_try_shrink(BDRVPCacheState *s)
 {
     while (s->lreq.curr_size > s->cfg.lreq_pool_size) {
         LRNode *rmv_node;
-            /* XXX: need to filter large requests */
-        if (QTAILQ_EMPTY(&s->lreq.lru.list)) {
-            DPRINTF("lru lreq list is empty, but curr_size: %d\n",
-                    s->lreq.curr_size);
-            break;
-        }
+        assert(!QTAILQ_EMPTY(&s->lreq.lru.list));
 
         qemu_co_mutex_lock(&s->lreq.lru.lock);
         rmv_node = LRNODE(QTAILQ_LAST(&s->lreq.lru.list, lru_head));
@@ -943,6 +946,23 @@ static void pcache_readahead_request(BlockDriverState *bs, 
PrefCacheAIOCB *acb)
     pcache_send_acb_request_list(bs, acb_readahead);
 }
 
+static inline bool pcache_skip_aio_read(BlockDriverState *bs,
+                                        uint64_t sector_num,
+                                        uint32_t nb_sectors)
+{
+    BDRVPCacheState *s = bs->opaque;
+
+    if (nb_sectors > s->cfg.max_aio_size) {
+        return true;
+    }
+
+    if (bdrv_nb_sectors(bs) < sector_num + nb_sectors) {
+        return true;
+    }
+
+    return false;
+}
+
 static BlockAIOCB *pcache_aio_readv(BlockDriverState *bs,
                                     int64_t sector_num,
                                     QEMUIOVector *qiov,
@@ -950,9 +970,16 @@ static BlockAIOCB *pcache_aio_readv(BlockDriverState *bs,
                                     BlockCompletionFunc *cb,
                                     void *opaque)
 {
-    PrefCacheAIOCB *acb = pcache_aio_get(bs, sector_num, qiov, nb_sectors, cb,
-                                         opaque, PCACHE_AIO_READ);
-    int32_t status = pcache_prefetch(acb);
+    PrefCacheAIOCB *acb;
+    int32_t status;
+
+    if (pcache_skip_aio_read(bs, sector_num, nb_sectors)) {
+        return bdrv_aio_readv(bs->file, sector_num, qiov, nb_sectors,
+                              cb, opaque);
+    }
+    acb = pcache_aio_get(bs, sector_num, qiov, nb_sectors, cb,
+                         opaque, PCACHE_AIO_READ);
+    status = pcache_prefetch(acb);
     if (status == PREFETCH_NEW_NODE) {
         BlockAIOCB *ret = bdrv_aio_readv(bs->file, sector_num, qiov, 
nb_sectors,
                                          cb, opaque);
@@ -993,9 +1020,12 @@ static void pcache_state_init(QemuOpts *opts, 
BDRVPCacheState *s)
                                             PCACHE_DEFAULT_CACHE_SIZE);
     uint64_t readahead_size = qemu_opt_get_size(opts, 
PCACHE_OPT_READAHEAD_SIZE,
                                                 PCACHE_DEFAULT_READAHEAD_SIZE);
+    uint64_t max_aio_size = qemu_opt_get_size(opts, PCACHE_OPT_MAX_AIO_SIZE,
+                                              PCACHE_DEFAULT_MAX_AIO_SIZE);
     DPRINTF("pcache configure:\n");
     DPRINTF("pcache-full-size = %jd\n", cache_size);
     DPRINTF("readahead_size = %jd\n", readahead_size);
+    DPRINTF("max_aio_size = %jd\n", max_aio_size);
 
     s->pcache.tree.root = RB_ROOT;
     qemu_co_mutex_init(&s->pcache.tree.lock);
@@ -1012,6 +1042,7 @@ static void pcache_state_init(QemuOpts *opts, 
BDRVPCacheState *s)
     s->cfg.cache_size = cache_size >> BDRV_SECTOR_BITS;
     s->cfg.readahead_size = readahead_size >> BDRV_SECTOR_BITS;
     s->cfg.lreq_pool_size = PCACHE_DEFAULT_POOL_STAT_SIZE >> BDRV_SECTOR_BITS;
+    s->cfg.max_aio_size = max_aio_size >> BDRV_SECTOR_BITS;
 
 #ifdef PCACHE_DEBUG
     QTAILQ_INIT(&s->death_node_list);
-- 
2.8.3