On Wed, Feb 20, 2013 at 11:27:47AM +0100, Kevin Wolf wrote: > On Tue, Feb 19, 2013 at 04:45:00PM +0100, Stefan Hajnoczi wrote: > > Users have reported that qcow2 internal snapshot creation is slow. I filed > > a > > bug report at https://bugs.launchpad.net/qemu/+bug/1126369. > > > > This patch series reduces the time for qcow2 internal snapshot creation > > significantly, from more than 3 minutes to under 1 second. > > > > In the process of removing unnecessary cache flushes, I also stumbled upon > > instances of bdrv_flush(bs->file) where we really want to flush metadata > > updates. Since qcow2 caches metadata this actually does not write out the > > metadata updates to disk! The fix is either bdrv_flush(bs) or a more > > specific > > cache flush (e.g. refcount block cache). > > > > This series passes qemu-iotests. > > > > Stefan Hajnoczi (6): > > qcow2: flush refcount cache correctly in alloc_refcount_block() > > qcow2: flush refcount cache correctly in qcow2_write_snapshots() > > qcow2: flush caches in qcow2_alloc_bytes() > > qcow2: flush in qcow2_update_snapshot_refcount() > > qcow2: drop flush in update_cluster_refcount() > > qcow2: drop unnecessary flush in qcow2_update_snapshot_refcount() > > > > block/qcow2-refcount.c | 12 +++--------- > > block/qcow2-snapshot.c | 7 +------ > > 2 files changed, 4 insertions(+), 15 deletions(-) > > You touch a few bdrv_flush() callers that don't check the return value. > Could you use the opportunity to fix that as well?
Sure, will send a v2. Stefan
