Description of problem:
Set the option bps_wr_max in order to limit write throughput during bursts in qemu command,but it does not work by the test of fio.

Version-Release number of selected component (if applicable):
Host kernel:3.10.0-543.el7.ppc64le 
qemu: qemu-kvm-rhev-2.8.0-2.el7 
slof: SLOF-20160223-6.gitdbbfda4.el7 
Guest kernel:3.10.0-543.el7.ppc64

How reproducible:
100%

Steps to Reproduce:
1.boot a guest with a virtio scsi disk and set the throttle value
eg:
/usr/libexec/qemu-kvm \
-name RHEL7-8398 \
-M pseries-rhel7.4.0 \
-m 64G \
-smp 4 \
-boot menu=on,order=c \
-device virtio-scsi-pci,id=virtio_scsi_pci0,bus=pci.0,addr=06 \
-drive file=/home/hyx/os/RHEL-7.3-20161019.0-Server-ppc64-dvd1.iso,if=none,media=cdrom,id=image0 \
-device scsi-cd,id=scsi-cd0,drive=image0,channel=0,scsi-id=0,lun=0,bootindex=1 \
-drive file=/home/hyx/image/RHEL7-8398-2-25G.raw,if=none,media=disk,format=raw,cache=none,iops_rd=10000,iops_rd_max=40000,iops_wr=10000,iops_wr_max=40000,bps_rd=1024000,bps_rd_max=2048000,bps_wr=1024000,bps_wr_max=2048000,id=image2 \
-device scsi-hd,id=scsi-hd2,drive=image2,channel=0,scsi-id=0,lun=1 \
-drive file=/home/hyx/image/RHEL7-8398-20G.raw,if=none,media=disk,format=raw,id=image1 \
-device scsi-hd,id=scsi-hd1,drive=image1,channel=0,scsi-id=0,lun=2,bootindex=0 \
-device nec-usb-xhci,id=xhci \
-drive file=/home/hyx/image/ubs-1G.raw,if=none,id=stick,bps_rd=102400,iops_rd=100,bps_wr=102400,iops_wr=100 \
-device usb-storage,removable=on,bus=xhci.0,drive=stick \
-netdev tap,id=hostnet0,script=/etc/qemu-ifup \
-device spapr-vlan,netdev=hostnet0,id=virtio-net-pci0,mac=70:e2:84:14:0e:23 \
-rtc base=utc,clock=vm \
-monitor stdio \
-serial unix:./sock2,server,nowait \
-qmp tcp:0:3000,server,nowait \
-device usb-tablet \
-vnc :1

2.run fio in guest
eg:
fio --filename=/dev/sdb --direct=1 --rw=write --bs=64k --size=1000M --name=test --iodepth=1 --runtime=1

Actual results:
[root@dhcp112-199 ~]# fio --filename=/dev/sdb --direct=1 --rw=write --bs=64k --size=1000M --name=test --iodepth=1 --runtime=1
test: (g=0): rw=write, bs=64K-64K/64K-64K/64K-64K, ioengine=sync, iodepth=1
fio-2.2.8
Starting 1 process
Jobs: 1 (f=1)
test: (groupid=0, jobs=1): err= 0: pid=6594: Thu Jan 19 22:38:25 2017
  write: io=3072.0KB, bw=3041.6KB/s, iops=47, runt=  1010msec
    clat (usec): min=486, max=104716, avg=21025.79, stdev=29149.76
     lat (usec): min=486, max=104717, avg=21026.56, stdev=29149.90
    clat percentiles (usec):
     |  1.00th=[  486],  5.00th=[ 1880], 10.00th=[ 1928], 20.00th=[ 2096],
     | 30.00th=[ 2192], 40.00th=[ 2352], 50.00th=[ 2576], 60.00th=[ 3152],
     | 70.00th=[23168], 80.00th=[63232], 90.00th=[64256], 95.00th=[67072],
     | 99.00th=[104960], 99.50th=[104960], 99.90th=[104960], 99.95th=[104960],
     | 99.99th=[104960]
    bw (KB  /s): min= 1005, max= 5120, per=100.00%, avg=3062.50, stdev=2909.74
    lat (usec) : 500=2.08%, 1000=2.08%
    lat (msec) : 2=8.33%, 4=50.00%, 10=4.17%, 50=8.33%, 100=22.92%
    lat (msec) : 250=2.08%
  cpu          : usr=0.00%, sys=0.00%, ctx=48, majf=0, minf=5
  IO depths    : 1=100.0%, 2=0.0%, 4=0.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
     submit    : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     complete  : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
     issued    : total=r=0/w=48/d=0, short=r=0/w=0/d=0, drop=r=0/w=0/d=0
     latency   : target=0, window=0, percentile=100.00%, depth=1

Run status group 0 (all jobs):
  WRITE: io=3072KB, aggrb=3041KB/s, minb=3041KB/s, maxb=3041KB/s, mint=1010msec, maxt=1010msec

Disk stats (read/write):
  sdb: ios=16/46, merge=0/0, ticks=10/890, in_queue=910, util=91.27%

Expected results:
The result of bw(Bandwidth) should be limit to 2048KB/s.

Additional info: