[Qemu-block] [PATCH RFC v2 09/22] block/pcache: separation AIOCB on requests

[Pavel Butsykin]

for case when the cache partially covers request we are part of the request
is filled from the cache, and the other part request from disk. Also add
reference counting for nodes, as way to maintain multithreading.

There is still no full synchronization in multithreaded mode.

Signed-off-by: Pavel Butsykin <address@hidden>
---
 block/pcache.c | 169 ++++++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 155 insertions(+), 14 deletions(-)

diff --git a/block/pcache.c b/block/pcache.c
index 28bd056..6114289 100644
--- a/block/pcache.c
+++ b/block/pcache.c
@@ -58,7 +58,10 @@ typedef struct BlockNode {
 typedef struct PCNode {
     BlockNode cm;
 
+    uint32_t                 status;
+    uint32_t                 ref;
     uint8_t                  *data;
+    CoMutex                  lock;
 } PCNode;
 
 typedef struct ReqStor {
@@ -95,9 +98,23 @@ typedef struct PrefCacheAIOCB {
     uint64_t sector_num;
     uint32_t nb_sectors;
     int      aio_type;
+    struct {
+        QTAILQ_HEAD(req_head, PrefCachePartReq) list;
+        CoMutex lock;
+    } requests;
     int      ret;
 } PrefCacheAIOCB;
 
+typedef struct PrefCachePartReq {
+    uint64_t sector_num;
+    uint32_t nb_sectors;
+
+    QEMUIOVector qiov;
+    PCNode *node;
+    PrefCacheAIOCB *acb;
+    QTAILQ_ENTRY(PrefCachePartReq) entry;
+} PrefCachePartReq;
+
 static const AIOCBInfo pcache_aiocb_info = {
     .aiocb_size = sizeof(PrefCacheAIOCB),
 };
@@ -126,8 +143,39 @@ static QemuOptsList runtime_opts = {
 #define MB_BITS 20
 #define PCACHE_DEFAULT_CACHE_SIZE (4 << MB_BITS)
 
+enum {
+    NODE_SUCCESS_STATUS = 0,
+    NODE_WAIT_STATUS    = 1,
+    NODE_REMOVE_STATUS  = 2,
+    NODE_GHOST_STATUS   = 3 /* only for debugging */
+};
+
 #define PCNODE(_n) ((PCNode *)(_n))
 
+static inline void pcache_node_unref(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);
+
+        node->status = NODE_GHOST_STATUS;
+        g_free(node->data);
+        g_slice_free1(sizeof(*node), node);
+    }
+}
+
+static inline PCNode *pcache_node_ref(PCNode *node)
+{
+    assert(node->status == NODE_SUCCESS_STATUS ||
+           node->status == NODE_WAIT_STATUS);
+    assert(atomic_read(&node->ref) == 0);/* XXX: only for sequential requests 
*/
+    atomic_inc(&node->ref);
+
+    return node;
+}
+
 static int pcache_key_cmp(const RbNodeKey *key1, const RbNodeKey *key2)
 {
     assert(key1 != NULL);
@@ -184,13 +232,7 @@ static void *node_insert(struct RbRoot *root, BlockNode 
*node)
 
 static inline PCNode *pcache_node_insert(struct RbRoot *root, PCNode *node)
 {
-    return node_insert(root, &node->cm);
-}
-
-static inline void pcache_node_free(PCNode *node)
-{
-    g_free(node->data);
-    g_slice_free1(sizeof(*node), node);
+    return pcache_node_ref(node_insert(root, &node->cm));
 }
 
 static inline void *pcache_node_alloc(RbNodeKey* key)
@@ -199,6 +241,9 @@ static inline void *pcache_node_alloc(RbNodeKey* key)
 
     node->cm.sector_num = key->num;
     node->cm.nb_sectors = key->size;
+    node->ref = 0;
+    node->status = NODE_WAIT_STATUS;
+    qemu_co_mutex_init(&node->lock);
     node->data = g_malloc(node->cm.nb_sectors << BDRV_SECTOR_BITS);
 
     return node;
@@ -206,6 +251,12 @@ static inline void *pcache_node_alloc(RbNodeKey* key)
 
 static void pcache_node_drop(BDRVPCacheState *s, PCNode *node)
 {
+    uint32_t prev_status = atomic_xchg(&node->status, NODE_REMOVE_STATUS);
+    if (prev_status == NODE_REMOVE_STATUS) {
+        return;
+    }
+    assert(prev_status != NODE_GHOST_STATUS);
+
     atomic_sub(&s->pcache.curr_size, node->cm.nb_sectors);
 
     qemu_co_mutex_lock(&s->pcache.lru.lock);
@@ -216,7 +267,7 @@ static void pcache_node_drop(BDRVPCacheState *s, PCNode 
*node)
     rb_erase(&node->cm.rb_node, &s->pcache.tree.root);
     qemu_co_mutex_unlock(&s->pcache.tree.lock);
 
-    pcache_node_free(node);
+    pcache_node_unref(node);
 }
 
 static void pcache_try_shrink(BDRVPCacheState *s)
@@ -234,6 +285,30 @@ static void pcache_try_shrink(BDRVPCacheState *s)
     }
 }
 
+static PrefCachePartReq *pcache_req_get(PrefCacheAIOCB *acb, PCNode *node)
+{
+    PrefCachePartReq *req = g_slice_alloc(sizeof(*req));
+
+    req->nb_sectors = node->cm.nb_sectors;
+    req->sector_num = node->cm.sector_num;
+    req->node = node;
+    req->acb = acb;
+
+    assert(acb->sector_num <= node->cm.sector_num + node->cm.nb_sectors);
+
+    qemu_iovec_init(&req->qiov, 1);
+    qemu_iovec_add(&req->qiov, node->data,
+                   node->cm.nb_sectors << BDRV_SECTOR_BITS);
+    return req;
+}
+
+static inline void push_node_request(PrefCacheAIOCB *acb, PCNode *node)
+{
+    PrefCachePartReq *req = pcache_req_get(acb, node);
+
+    QTAILQ_INSERT_HEAD(&acb->requests.list, req, entry);
+}
+
 static inline void pcache_lru_node_up(BDRVPCacheState *s, PCNode *node)
 {
     qemu_co_mutex_lock(&s->pcache.lru.lock);
@@ -253,16 +328,17 @@ static bool pcache_node_find_and_create(PrefCacheAIOCB 
*acb, RbNodeKey *key,
     found = pcache_node_insert(&s->pcache.tree.root, new_node);
     qemu_co_mutex_unlock(&s->pcache.tree.lock);
     if (found != new_node) {
-        pcache_node_free(new_node);
-        pcache_lru_node_up(s, found);
+        g_free(new_node->data);
+        g_slice_free1(sizeof(*new_node), new_node);
+        if (found->status == NODE_SUCCESS_STATUS) {
+            pcache_lru_node_up(s, found);
+        }
         *out_node = found;
         return false;
     }
     atomic_add(&s->pcache.curr_size, new_node->cm.nb_sectors);
 
-    qemu_co_mutex_lock(&s->pcache.lru.lock);
-    QTAILQ_INSERT_HEAD(&s->pcache.lru.list, &new_node->cm, entry);
-    qemu_co_mutex_unlock(&s->pcache.lru.lock);
+    push_node_request(acb, new_node);
 
     pcache_try_shrink(s);
 
@@ -291,6 +367,7 @@ static void pcache_pickup_parts_of_cache(PrefCacheAIOCB 
*acb, PCNode *node,
             up_size = lc_key.size;
 
             if (!pcache_node_find_and_create(acb, &lc_key, &new_node)) {
+                pcache_node_unref(node);
                 node = new_node;
                 continue;
             }
@@ -300,6 +377,8 @@ static void pcache_pickup_parts_of_cache(PrefCacheAIOCB 
*acb, PCNode *node,
         /* XXX: node read */
         up_size = MIN(node->cm.sector_num + node->cm.nb_sectors - num, size);
 
+        pcache_node_unref(node);
+
         size -= up_size;
         num += up_size;
         if (size != 0) {
@@ -336,6 +415,8 @@ static int32_t pcache_prefetch(PrefCacheAIOCB *acb)
         node->cm.sector_num + node->cm.nb_sectors >= acb->sector_num +
                                                      acb->nb_sectors)
     {
+        /* XXX: node read */
+        pcache_node_unref(node);
         return PREFETCH_FULL_UP;
     }
     pcache_pickup_parts_of_cache(acb, node, key.num, key.size);
@@ -343,10 +424,56 @@ static int32_t pcache_prefetch(PrefCacheAIOCB *acb)
     return PREFETCH_PART_UP;
 }
 
+static void pcache_node_submit(PrefCachePartReq *req)
+{
+    PCNode *node = req->node;
+    BDRVPCacheState *s = req->acb->s;
+
+    assert(node != NULL);
+    assert(atomic_read(&node->ref) != 0);
+    assert(node->data != NULL);
+
+    qemu_co_mutex_lock(&node->lock);
+    if (node->status == NODE_WAIT_STATUS) {
+        qemu_co_mutex_lock(&s->pcache.lru.lock);
+        QTAILQ_INSERT_HEAD(&s->pcache.lru.list, &node->cm, entry);
+        qemu_co_mutex_unlock(&s->pcache.lru.lock);
+
+        node->status = NODE_SUCCESS_STATUS;
+    }
+    qemu_co_mutex_unlock(&node->lock);
+}
+
+static void pcache_merge_requests(PrefCacheAIOCB *acb)
+{
+    PrefCachePartReq *req, *next;
+
+    qemu_co_mutex_lock(&acb->requests.lock);
+    QTAILQ_FOREACH_SAFE(req, &acb->requests.list, entry, next) {
+        QTAILQ_REMOVE(&acb->requests.list, req, entry);
+
+        assert(req != NULL);
+        assert(req->node->status == NODE_WAIT_STATUS);
+
+        pcache_node_submit(req);
+
+        /* XXX: pcache read */
+
+        pcache_node_unref(req->node);
+
+        g_slice_free1(sizeof(*req), req);
+    }
+    qemu_co_mutex_unlock(&acb->requests.lock);
+}
+
 static void pcache_aio_cb(void *opaque, int ret)
 {
     PrefCacheAIOCB *acb = opaque;
 
+    if (acb->aio_type & QEMU_AIO_READ) {
+        pcache_merge_requests(acb);
+    }
+
     acb->common.cb(acb->common.opaque, ret);
 
     qemu_aio_unref(acb);
@@ -366,6 +493,9 @@ static PrefCacheAIOCB *pcache_aio_get(BlockDriverState *bs, 
int64_t sector_num,
     acb->aio_type = type;
     acb->ret = 0;
 
+    QTAILQ_INIT(&acb->requests.list);
+    qemu_co_mutex_init(&acb->requests.lock);
+
     return acb;
 }
 
@@ -445,6 +575,17 @@ fail:
     return ret;
 }
 
+static void pcache_node_check_and_free(BDRVPCacheState *s, PCNode *node)
+{
+    assert(node->status == NODE_SUCCESS_STATUS);
+    assert(node->ref == 0);
+
+    node->status = NODE_REMOVE_STATUS;
+    rb_erase(&node->cm.rb_node, &s->pcache.tree.root);
+    g_free(node->data);
+    g_slice_free1(sizeof(*node), node);
+}
+
 static void pcache_close(BlockDriverState *bs)
 {
     uint32_t cnt = 0;
@@ -452,7 +593,7 @@ static void pcache_close(BlockDriverState *bs)
     BlockNode *node, *next;
     QTAILQ_FOREACH_SAFE(node, &s->pcache.lru.list, entry, next) {
         QTAILQ_REMOVE(&s->pcache.lru.list, node, entry);
-        pcache_node_free(PCNODE(node));
+        pcache_node_check_and_free(s, PCNODE(node));
         cnt++;
     }
     DPRINTF("used %d nodes\n", cnt);
-- 
2.8.3