[PATCH 2/2] selftests: ublk: make the fault_inject delay a pure timeout

[Qiliang Yuan]

ublk_fault_inject_queue_io() queues the delay of each I/O as an
IORING_OP_TIMEOUT with a completion count of 1. Such a timeout also
completes as soon as any other CQE is posted on the ring.

With more than one I/O in flight, the completion of one I/O ends the
delay of the others, and ublk_fault_inject_tgt_io_done() reports every
early completion as "unexpected cqe res 0".

Pass a count of 0 so that only the expiry of the timer completes the
timeout.

fio 4k random reads for 10 s at queue depth 4 on a fault_inject device
with --delay_us 1000000:

                            before      after   expected
  I/Os                     2263170         40         40
  mean latency             16.3 us    1.000 s        1 s
  "unexpected cqe res 0"   2263169          0          0

Fixes: 81586652bb1f ("selftests: ublk: add generic_06 for covering fault inject")
Signed-off-by: Qiliang Yuan <odys.yuan@xxxxxxxxx>
---
 tools/testing/selftests/ublk/fault_inject.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/ublk/fault_inject.c b/tools/testing/selftests/ublk/fault_inject.c
index e055f51a65447..4b59f17a918c0 100644
--- a/tools/testing/selftests/ublk/fault_inject.c
+++ b/tools/testing/selftests/ublk/fault_inject.c
@@ -92,7 +92,7 @@ static int ublk_fault_inject_queue_io(struct ublk_thread *t,
 	 * reads it only when the SQE is submitted.
 	 */
 	ublk_io_alloc_sqes(t, &sqe, 1);
-	io_uring_prep_timeout(sqe, &opts->delay, 1, 0);
+	io_uring_prep_timeout(sqe, &opts->delay, 0, 0);
 	sqe->user_data = build_user_data(tag, ublksrv_get_op(iod), 0, q->q_id, 1);
 
 	ublk_queued_tgt_io(t, q, tag, 1);

-- 
2.43.0