[Qemu-devel] [PATCH] qcow2-cache: conditionally call bdrv_flush() in qcow2_cache_flush()

[Zhang Haoyu]

Needless to call bdrv_flush() in qcow2_cache_flush()
if no cache entry is dirty.

Signed-off-by: Zhang Haoyu <address@hidden>
---
 block/qcow2-cache.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index 904f6b1..09ee155 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -110,10 +110,6 @@ static int qcow2_cache_entry_flush(BlockDriverState *bs, 
Qcow2Cache *c, int i)
     BDRVQcowState *s = bs->opaque;
     int ret = 0;
 
-    if (!c->entries[i].dirty || !c->entries[i].offset) {
-        return 0;
-    }
-
     trace_qcow2_cache_entry_flush(qemu_coroutine_self(),
                                   c == s->l2_table_cache, i);
 
@@ -166,19 +162,23 @@ int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c)
 {
     BDRVQcowState *s = bs->opaque;
     int result = 0;
+    bool need_bdrv_flush = false;
     int ret;
     int i;
 
     trace_qcow2_cache_flush(qemu_coroutine_self(), c == s->l2_table_cache);
 
     for (i = 0; i < c->size; i++) {
-        ret = qcow2_cache_entry_flush(bs, c, i);
-        if (ret < 0 && result != -ENOSPC) {
-            result = ret;
+        if (c->entries[i].dirty && c->entries[i].offset) {
+            ret = qcow2_cache_entry_flush(bs, c, i);
+            if (ret < 0 && result != -ENOSPC) {
+                result = ret;
+            }
+            need_bdrv_flush = true;
         }
     }
 
-    if (result == 0) {
+    if (need_bdrv_flush && result == 0) {
         ret = bdrv_flush(bs->file);
         if (ret < 0) {
             result = ret;
@@ -289,9 +289,11 @@ static int qcow2_cache_do_get(BlockDriverState *bs, 
Qcow2Cache *c,
         return i;
     }
 
-    ret = qcow2_cache_entry_flush(bs, c, i);
-    if (ret < 0) {
-        return ret;
+    if (c->entries[i].dirty && c->entries[i].offset) {
+        ret = qcow2_cache_entry_flush(bs, c, i);
+        if (ret < 0) {
+            return ret;
+        }
     }
 
     trace_qcow2_cache_get_read(qemu_coroutine_self(),
-- 
1.7.12.4