RE: [PATCH V2 4/8] block: null_blk: introduce module parameter of 'g_global_tags'

[Don Brace <don.brace@microsemi.com>]

> This patch introduces the parameter of 'g_global_tags' so that we can
> test this feature by null_blk easiy.
>=20
> Not see obvious performance drop with global_tags when the whole hw
> depth is kept as same:
>=20
> 1) no 'global_tags', each hw queue depth is 1, and 4 hw queues
> modprobe null_blk queue_mode=3D2 nr_devices=3D4 shared_tags=3D1 global_ta=
gs=3D0
> submit_queues=3D4 hw_queue_depth=3D1
>=20
> 2) 'global_tags', global hw queue depth is 4, and 4 hw queues
> modprobe null_blk queue_mode=3D2 nr_devices=3D4 shared_tags=3D1 global_ta=
gs=3D1
> submit_queues=3D4 hw_queue_depth=3D4
>=20
> 3) fio test done in above two settings:
>    fio --bs=3D4k --size=3D512G  --rw=3Drandread --norandommap --direct=3D=
1 --
> ioengine=3Dlibaio --iodepth=3D4 --runtime=3D$RUNTIME --group_reporting=3D=
1  --
> name=3Dnullb0 --filename=3D/dev/nullb0 --name=3Dnullb1 --filename=3D/dev/=
nullb1 --
> name=3Dnullb2 --filename=3D/dev/nullb2 --name=3Dnullb3 --filename=3D/dev/=
nullb3
>=20
> 1M IOPS can be reached in both above tests which is done in one VM.
>=20
I am getting 1.1M IOPS for both cases.

Tested-by: Don Brace <don.brace@microsemi.com>