My NVME performance rabbit hole is confusing; one of my two identical drives is half the performance in hdparm -T; I swapped the drives in the slots and the performance follows the drive not the slot. PCIe looks fine with the same link speed/width. NVMe features (nvme get-feature /dev/nvme. -f 0 -H) are the same on both.
Oddly the *latency* is much lower on the slower drive?!! wtf?!