4K writes on nvme device vs that on ext4 running on nvme block device

[Bhattacharya, Indranil]

Hi,

I was recently doing some experiments using the nvme emulator (nvmeqemu) and I observed a curious thing. There was a marked degradation in write-throughput when I run FIO (multithreaded, O_DIRECT writes) on an ext4 filesystem that has been created on top of a nvme block device; as compared to the same tests which run directly on the nvme block device (i.e. without the filesystem in between).

I plan to repeat this test on a real nvme device as soon as I get one, but some insight from others on the following questions will be helpful:

	1) Have others seen the same on a real nvme device?
	2) If yes, any possible explanation for the same?

Thanks,
Indranil