coalescing in polling mode in 4.9

[Alex Nln]

Hello,

Enabling interrupt coalescing in nvme device, kernel 4.9 
significantly reduces performance when using polling mode.
When I enable coalescing, IOPS drops from 100K to 35K and 
latency jumps from 7 usec to 25 usec.

Shouldn't we expect performance boost in polling mode when
interrupt coalescing enabled? 


Device is Intel DC P3600
Coalescing enabled:  nvme set-feature /dev/nvme0 -f 8 -v 0x00ffff
fio-2.16 file:
[global]
iodepth=1
direct=1
ioengine=pvsync2
hipri
group_reporting
time_based
blocksize=4k
norandommap=1

[job1]
rw=read
filename=/dev/nvme0n1
name=raw=sequential-read
numjobs=1
runtime=60



Thanks