diff mbox

[4/8] qcow2: remove qcow2_cache_find_entry_to_replace()

Message ID a87d0ee8649f4df50595a064e8396e55c5402bf1.1431348770.git.berto@igalia.com
State New
Headers show

Commit Message

Alberto Garcia May 11, 2015, 12:54 p.m. UTC 
A cache miss means that the whole array was traversed and the entry
we were looking for was not found, so there's no need to traverse it
again in order to select an entry to replace.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
 block/qcow2-cache.c | 45 ++++++++++++++++-----------------------------
 1 file changed, 16 insertions(+), 29 deletions(-)
diff mbox

Patch

diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index 3a31895..2035cd8 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -242,51 +242,38 @@  int qcow2_cache_empty(BlockDriverState *bs, Qcow2Cache *c)
     return 0;
 }
 
-static int qcow2_cache_find_entry_to_replace(Qcow2Cache *c)
-{
-    int i;
-    uint64_t min_lru_counter = UINT64_MAX;
-    int min_index = -1;
-
-
-    for (i = 0; i < c->size; i++) {
-        if (c->entries[i].ref) {
-            continue;
-        }
-
-        if (c->entries[i].lru_counter < min_lru_counter) {
-            min_index = i;
-            min_lru_counter = c->entries[i].lru_counter;
-        }
-    }
-
-    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;
-}
-
 static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c,
     uint64_t offset, void **table, bool read_from_disk)
 {
     BDRVQcowState *s = bs->opaque;
     int i;
     int ret;
+    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) {
+        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 (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) {