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[Qemu-devel] [PATCH 4/4] qcow2: Get rid of additional sync on COW
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PATCH 4/4] qcow2: Get rid of additional sync on COW |
Date: |
Fri, 17 Sep 2010 18:18:38 +0200 |
We always have a sync for the refcount update when a new cluster is
allocated. If we move this past the COW, we can save an additional sync.
Signed-off-by: Kevin Wolf <address@hidden>
---
block/qcow2-cluster.c | 10 ++++++++--
1 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 66969c2..634ccef 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -422,7 +422,7 @@ static int copy_sectors(BlockDriverState *bs, uint64_t
start_sect,
&s->aes_encrypt_key);
}
BLKDBG_EVENT(bs->file, BLKDBG_COW_WRITE);
- ret = bdrv_write_sync(bs->file, (cluster_offset >> 9) + n_start,
+ ret = bdrv_write(bs->file, (cluster_offset >> 9) + n_start,
s->cluster_data, n);
if (ret < 0)
return ret;
@@ -721,6 +721,13 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs,
QCowL2Meta *m)
(i << s->cluster_bits)) | QCOW_OFLAG_COPIED);
}
+ /*
+ * Before we update the L2 table to actually point to the new cluster, we
+ * need to be sure that the refcounts have been increased and COW was
+ * handled.
+ */
+ bdrv_flush(bs->file);
+
ret = write_l2_entries(bs, l2_table, l2_offset, l2_index, m->nb_clusters);
if (ret < 0) {
qcow2_l2_cache_reset(bs);
@@ -872,7 +879,6 @@ int qcow2_alloc_cluster_offset(BlockDriverState *bs,
uint64_t offset,
QLIST_REMOVE(m, next_in_flight);
return cluster_offset;
}
- bdrv_flush(bs->file);
/* save info needed for meta data update */
m->offset = offset;
--
1.7.2.2