Fio high IOPS measurement mistake

[Vladislav Bolkhovitin <vst@vlnb.net>]

Hello,

I'm currently looking at one NVRAM device, and during fio tests noticed that each fio
thread consumes 30% of user space CPU. I'm using ioengine=libaio, buffered=0, sync=0
and direct=1, so user space CPU consumption should be virtually zero.

That 30% user CPU consumption makes me suspect that this is overhead for internal fio
housekeeping, i.e., scientifically speaking, fio instrumental measurement mistake (I
hope, I'm using correct English terms).

Can anybody comment it and suggest how to decrease this user space CPU consumption?

Here is my full fio job:

[global]
ioengine=libaio
buffered=0
sync=0
direct=1
randrepeat=1
softrandommap=1
rw=randread
bs=4k
filename=./nvram (it's a link to a block device)
exitall=1
thread=1
disable_lat=1
disable_slat=1
disable_clat=1
loops=10
iodepth=16

[file1]

[file2]

I'm working on million+ IOPS range.

Thanks,
Vlad