Hi Ming,
I'll have a look.
BTW, are you intentionally using scsi_debug over null_blk? null_blk
supports shared sbitmap as well, and performance figures there are
generally higher than scsi_debug for similar fio settings.
Thanks,
john
EOM
IOPs
mq-deadline usr=21.72%, sys=44.18%, 423K
none usr=23.15%, sys=74.01% 450K
Today I re-run the scsi_debug test on two server hardwares(32cores, dual
numa nodes), and the CPU utilization issue can be reproduced, follow
the test result:
1) randread test on ibm-x3850x6[*] with deadline
|IOPS | FIO CPU util
------------------------------------------------
hosttags | 94k | usr=1.13%, sys=14.75%
------------------------------------------------
non hosttags | 124k | usr=1.12%, sys=10.65%,
2) randread test on ibm-x3850x6[*] with none
|IOPS | FIO CPU util
------------------------------------------------
hosttags | 120k | usr=0.89%, sys=6.55%
------------------------------------------------
non hosttags | 121k | usr=1.07%, sys=7.35%
------------------------------------------------
*:
- that is the machine Yanhui reported VM cpu utilization increased by 20%
- kernel: latest linus tree(v5.12-rc7, commit: 7f75285ca57)
- also run same test on another 32cores machine, IOPS drop isn't
observed, but CPU utilization is increased obviously
3) test script
#/bin/bash
run_fio() {
RTIME=$1
JOBS=$2
DEVS=$3
BS=$4
QD=64
BATCH=16
fio --bs=$BS --ioengine=libaio \
--iodepth=$QD \
--iodepth_batch_submit=$BATCH \
--iodepth_batch_complete_min=$BATCH \
--filename=$DEVS \
--direct=1 --runtime=$RTIME --numjobs=$JOBS --rw=randread \
--name=test --group_reporting
}
SCHED=$1
NRQS=`getconf _NPROCESSORS_ONLN`
rmmod scsi_debug
modprobe scsi_debug host_max_queue=128 submit_queues=$NRQS virtual_gb=256
sleep 2
DEV=`lsscsi | grep scsi_debug | awk '{print $6}'`
echo $SCHED >/sys/block/`basename $DEV`/queue/scheduler
echo 128 >/sys/block/`basename $DEV`/device/queue_depth
run_fio 20 16 $DEV 8K
rmmod scsi_debug
modprobe scsi_debug max_queue=128 submit_queues=1 virtual_gb=256
sleep 2
DEV=`lsscsi | grep scsi_debug | awk '{print $6}'`
echo $SCHED >/sys/block/`basename $DEV`/queue/scheduler
echo 128 >/sys/block/`basename $DEV`/device/queue_depth
run_fio 20 16 $DEV 8k
