Re: [PATCH v2 3/3] qcow2: handle_dependencies(): relax conflict detection

[Eric Blake]

On Tue, Aug 24, 2021 at 01:15:17PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> There is no conflict and no dependency if we have parallel writes to
> different subclusters of one cluster when the cluster itself is already
> allocated. So, relax extra dependency.
> 
...
> So small writes are more independent now and that helps to keep deeper
> io queue which improves performance.
> 
> 271 iotest output becomes racy for three allocation in one cluster.
> Second and third writes may finish in different order. Second and
> third requests don't depend on each other any more. Still they both
> depend on first request anyway. Filter out second and third write
> offsets to cover both possible outputs.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/qcow2-cluster.c      | 11 +++++++++++
>  tests/qemu-iotests/271     |  5 ++++-
>  tests/qemu-iotests/271.out |  4 ++--
>  3 files changed, 17 insertions(+), 3 deletions(-)
> 

> +++ b/tests/qemu-iotests/271
> @@ -893,7 +893,10 @@ EOF
>  }
>  
>  _make_test_img -o extended_l2=on 1M
> -_concurrent_io     | $QEMU_IO | _filter_qemu_io
> +# Second an third writes in _concurrent_io() are independent and may finish 
> in

and

> +# different order. So, filter offset out to match both possible variants.
> +_concurrent_io     | $QEMU_IO | _filter_qemu_io | \
> +    $SED -e 's/\(20480\|40960\)/OFFSET/'
>  _concurrent_verify | $QEMU_IO | _filter_qemu_io
>

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org