> This patch introduces the parameter of 'g_global_tags' so that we can > test this feature by null_blk easiy. > > Not see obvious performance drop with global_tags when the whole hw > depth is kept as same: > > 1) no 'global_tags', each hw queue depth is 1, and 4 hw queues > modprobe null_blk queue_mode=2 nr_devices=4 shared_tags=1 global_tags=0 > submit_queues=4 hw_queue_depth=1 > > 2) 'global_tags', global hw queue depth is 4, and 4 hw queues > modprobe null_blk queue_mode=2 nr_devices=4 shared_tags=1 global_tags=1 > submit_queues=4 hw_queue_depth=4 > > 3) fio test done in above two settings: > fio --bs=4k --size=512G --rw=randread --norandommap --direct=1 -- > ioengine=libaio --iodepth=4 --runtime=$RUNTIME --group_reporting=1 -- > name=nullb0 --filename=/dev/nullb0 --name=nullb1 --filename=/dev/nullb1 -- > name=nullb2 --filename=/dev/nullb2 --name=nullb3 --filename=/dev/nullb3 > > 1M IOPS can be reached in both above tests which is done in one VM. > I am getting 1.1M IOPS for both cases. Tested-by: Don Brace <don.brace@xxxxxxxxxxxxx>
