Re: [PATCH 6/7] iotests/129: Limit mirror job's buffer size

[Eric Blake <eblake@redhat.com>]

On 1/13/21 8:06 AM, Max Reitz wrote:
> Issuing 'stop' on the VM drains all nodes.  If the mirror job has many
> large requests in flight, this may lead to significant I/O that looks a
> bit like the job is being drained.
> 
> We can limit the I/O in flight by limiting the buffer size, so mirror
> will make very little progress during the 'stop' drain.
> 
> (We do not need to do anything about commit, which has a buffer size of
> 512 kB by default; or backup, which goes cluster by cluster.  Once we
> have asynchronous requests for backup, that will change, but then we can
> fine-tune the backup job to only perform a single request on a very
> small chunk, too.)
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  tests/qemu-iotests/129 | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

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

> 
> diff --git a/tests/qemu-iotests/129 b/tests/qemu-iotests/129
> index e6753c90ef..c3ad584ba2 100755
> --- a/tests/qemu-iotests/129
> +++ b/tests/qemu-iotests/129
> @@ -69,7 +69,7 @@ class TestStopWithBlockJob(iotests.QMPTestCase):
>      def test_drive_mirror(self):
>          self.do_test_stop("drive-mirror", device="drive0",
>                            target=self.target_img, format=iotests.imgfmt,
> -                          sync="full")
> +                          sync="full", buf_size=65536)
>  
>      def test_drive_backup(self):
>          self.do_test_stop("drive-backup", device="drive0",
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org