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

From: Max Reitz
Subject: [PATCH 6/7] iotests/129: Limit mirror job's buffer size
Date: Wed, 13 Jan 2021 15:06:15 +0100

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(-)

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",

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