To expand on the batching details, I haven't seen exactly what he's doing here, but historically the numbers quoted are from benchmarks that submit something like 128 total queue depth in alternating batches of 64. The disks hit max performance with a much lower queue depth than 64. So it's very unrealistic perfect batching that you'll never see in a real application. The workload is only a useful tool for optimizing the code, which is exactly what he's using it for.

The Intel Optane drives he's testing with hit max performance at pretty low queue depths, but flash-based SSDs with similar throughput will require those high queue depths.

I think you need batching for the nvme doorbell alone at anything close to these kinds of rates...

For some workloads it's not that hard to have that deep queues. What's harder is to know when to use them and when not. There's really not enough information available to make any of this self-tuning.