qcow2_cache_flush() calls bdrv_flush() unconditionally after writing
cache entries of a particular cache. This can lead to as many as
2 additional fdatasyncs inside bdrv_flush.
We can simply skip all fdatasync calls inside qcow2_co_flush_to_os
as bdrv_flush for sure will do the job. This seriously affects the
performance of database operations inside the guest.
Signed-off-by: Denis V. Lunev <d...@openvz.org>
CC: Pavel Borzenkov <pborzen...@virtuozzo.com>
CC: Kevin Wolf <kw...@redhat.com>
CC: Max Reitz <mre...@redhat.com>
---
block/qcow2-cache.c | 11 +++++++++--
block/qcow2.c | 4 ++--
block/qcow2.h | 1 +
3 files changed, 12 insertions(+), 4 deletions(-)
diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index 0fe8eda..6079c4a 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -226,7 +226,7 @@ static int qcow2_cache_entry_flush(BlockDriverState *bs,
Qcow2Cache *c, int i)
return 0;
}
-int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c)
+int qcow2_cache_flush_nosync(BlockDriverState *bs, Qcow2Cache *c)
{
BDRVQcow2State *s = bs->opaque;
int result = 0;
@@ -242,8 +242,15 @@ int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c)
}
}
+ return result;
+}
+
+int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c)
+{
+ int result = qcow2_cache_flush_nosync(bs, c);
+
if (result == 0) {
- ret = bdrv_flush(bs->file->bs);
+ int ret = bdrv_flush(bs->file->bs);
if (ret < 0) {
result = ret;
}
diff --git a/block/qcow2.c b/block/qcow2.c
index 38caa66..bb6b788 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2837,14 +2837,14 @@ static coroutine_fn int
qcow2_co_flush_to_os(BlockDriverState *bs)
int ret;
qemu_co_mutex_lock(&s->lock);
- ret = qcow2_cache_flush(bs, s->l2_table_cache);
+ ret = qcow2_cache_flush_nosync(bs, s->l2_table_cache);
if (ret < 0) {
qemu_co_mutex_unlock(&s->lock);
return ret;
}
if (qcow2_need_accurate_refcounts(s)) {
- ret = qcow2_cache_flush(bs, s->refcount_block_cache);
+ ret = qcow2_cache_flush_nosync(bs, s->refcount_block_cache);
if (ret < 0) {
qemu_co_mutex_unlock(&s->lock);
return ret;
diff --git a/block/qcow2.h b/block/qcow2.h
index a063a3c..0751225 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -583,6 +583,7 @@ int qcow2_cache_destroy(BlockDriverState* bs, Qcow2Cache
*c);
void qcow2_cache_entry_mark_dirty(BlockDriverState *bs, Qcow2Cache *c,
void *table);
int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache *c);
+int qcow2_cache_flush_nosync(BlockDriverState *bs, Qcow2Cache *c);
int qcow2_cache_set_dependency(BlockDriverState *bs, Qcow2Cache *c,
Qcow2Cache *dependency);
void qcow2_cache_depends_on_flush(Qcow2Cache *c);
--
2.1.4
