[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PATCH 12/13] qcow2: drop flush in update_cluster_refcount(
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PATCH 12/13] qcow2: drop flush in update_cluster_refcount() |
Date: |
Tue, 12 Mar 2013 15:41:18 +0100 |
From: Stefan Hajnoczi <address@hidden>
The update_cluster_refcount() function increments/decrements a cluster's
refcount and then returns the new refcount value.
There is no need to flush since both update_cluster_refcount() callers
already take care of this:
1. qcow2_alloc_bytes() calls update_cluster_refcount() when compressed
sectors will be appended to an existing cluster with enough free
space. qcow2_alloc_bytes() already flushes so there is no need to do
so in update_cluster_refcount().
2. qcow2_update_snapshot_refcount() sets a cache dependency on refcounts
if it needs to update L2 entries. It also flushes before completing.
Removing this flush significantly speeds up qcow2 snapshot creation:
$ qemu-img create -f qcow2 test.qcow2 -o size=50G,preallocation=metadata
$ time qemu-img snapshot -c new test.qcow2
Time drops from more than 3 minutes to under 1 second.
Signed-off-by: Stefan Hajnoczi <address@hidden>
Signed-off-by: Kevin Wolf <address@hidden>
---
block/qcow2-refcount.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 3d29d30..92519ea 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -532,8 +532,6 @@ static int update_cluster_refcount(BlockDriverState *bs,
return ret;
}
- bdrv_flush(bs->file);
-
return get_refcount(bs, cluster_index);
}
--
1.8.1.4
- [Qemu-devel] [PATCH 08/13] qcow2: flush refcount cache correctly in alloc_refcount_block(), (continued)
- [Qemu-devel] [PATCH 08/13] qcow2: flush refcount cache correctly in alloc_refcount_block(), Kevin Wolf, 2013/03/12
- [Qemu-devel] [PATCH 06/13] block: Support driver specific options in drive_init(), Kevin Wolf, 2013/03/12
- [Qemu-devel] [PATCH 03/13] Add qdict_clone_shallow(), Kevin Wolf, 2013/03/12
- [Qemu-devel] [PATCH 05/13] qemu-option: Add qemu_opts_absorb_qdict(), Kevin Wolf, 2013/03/12
- [Qemu-devel] [PATCH 09/13] qcow2: flush refcount cache correctly in qcow2_write_snapshots(), Kevin Wolf, 2013/03/12
- [Qemu-devel] [PATCH 11/13] qcow2: flush in qcow2_update_snapshot_refcount(), Kevin Wolf, 2013/03/12
- [Qemu-devel] [PATCH 10/13] qcow2: set L2 cache dependency in qcow2_alloc_bytes(), Kevin Wolf, 2013/03/12
- [Qemu-devel] [PATCH 07/13] qcow2: Allow lazy refcounts to be enabled on the command line, Kevin Wolf, 2013/03/12
- [Qemu-devel] [PATCH 12/13] qcow2: drop flush in update_cluster_refcount(),
Kevin Wolf <=
- [Qemu-devel] [PATCH 13/13] qcow2: drop unnecessary flush in qcow2_update_snapshot_refcount(), Kevin Wolf, 2013/03/12