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Bug 2079701

Summary: 100% CPU consumption in IOThread
Product: Red Hat Enterprise Linux 9 Reporter: qing.wang <qinwang>
Component: qemu-kvmAssignee: Stefan Hajnoczi <stefanha>
qemu-kvm sub component: virtio-blk,scsi QA Contact: qing.wang <qinwang>
Status: CLOSED DUPLICATE Docs Contact:
Severity: high    
Priority: high CC: coli, jinzhao, juzhang, kkiwi, kwolf, lijin, nsoffer, qzhang, virt-maint, xuwei
Version: 9.1Keywords: Regression
Target Milestone: rcFlags: pm-rhel: mirror+
Target Release: ---   
Hardware: x86_64   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2022-05-11 09:11:01 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description qing.wang 2022-04-28 06:33:59 UTC 
Description of problem:
100% CPU consumption in IOThread



Version-Release number of selected component (if applicable):

Red Hat Enterprise Linux release 9.1 Beta (Plow)
5.14.0-80.el9.x86_64
qemu-kvm-7.0.0-1.el9.x86_64
seabios-bin-1.16.0-1.el9.noarch

How reproducible:

100%
Steps to Reproduce:
1.boot vm with scsi disk iothread enabled
/usr/libexec/qemu-kvm \
  -name testvm \
  -machine q35 \
  -m  6G \
  -smp 2 \
  -cpu host,+kvm_pv_unhalt \
  -device ich9-usb-ehci1,id=usb1 \
  -device usb-tablet,id=usb-tablet1,bus=usb1.0,port=1 \
   \
   \
  -device pcie-root-port,id=pcie-root-port-0,multifunction=on,bus=pcie.0,addr=0x3,chassis=1 \
  -device pcie-root-port,id=pcie-root-port-1,port=0x1,addr=0x3.0x1,bus=pcie.0,chassis=2 \
  -device pcie-root-port,id=pcie-root-port-2,port=0x2,addr=0x3.0x2,bus=pcie.0,chassis=3 \
  -device pcie-root-port,id=pcie-root-port-3,port=0x3,addr=0x3.0x3,bus=pcie.0,chassis=4 \
  -device pcie-root-port,id=pcie-root-port-4,port=0x4,addr=0x3.0x4,bus=pcie.0,chassis=5 \
  -device pcie-root-port,id=pcie-root-port-5,port=0x5,addr=0x3.0x5,bus=pcie.0,chassis=6 \
  -device pcie-root-port,id=pcie-root-port-6,port=0x6,addr=0x3.0x6,bus=pcie.0,chassis=7 \
  -device pcie-root-port,id=pcie-root-port-7,port=0x7,addr=0x3.0x7,bus=pcie.0,chassis=8 \
  -device pcie-root-port,id=pcie_extra_root_port_0,bus=pcie.0,addr=0x4  \
  -object iothread,id=iothread0 \
  -device virtio-scsi-pci,id=scsi0,bus=pcie-root-port-4,iothread=iothread0 \
  \
  -blockdev driver=qcow2,file.driver=file,cache.direct=off,cache.no-flush=on,file.filename=/home/kvm_autotest_root/images/rhel900-64-virtio-scsi.qcow2,node-name=drive_image1   \
  -device scsi-hd,id=os,drive=drive_image1,bus=scsi0.0,bootindex=0,serial=OS_DISK   \
  \
  -vnc :5 \
  -monitor stdio \
  -qmp tcp:0:5955,server=on,wait=off \
  -device virtio-net-pci,mac=9a:b5:b6:b1:b2:b7,id=nic1,netdev=nicpci,bus=pcie-root-port-7 \
  -netdev tap,id=nicpci \

2.wait guest boot succeed,then wait 1 miniutes,check resource with top command

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND                                                         
 107116 root      20   0 8617572   1.9g  19852 S 100.3   3.0   5:30.62 qemu-kvm



Actual results:
qemu-kvm process have high cpu consumption
Expected results:
low cpu consumption 
Additional info:
  
Not issue found on
Red Hat Enterprise Linux release 9.0 (Plow)
5.14.0-70.13.1.el9_0.x86_64
qemu-kvm-6.2.0-11.el9_0.2.x86_64

Disable iothread will not hit this issue.
Comment 1 Stefan Hajnoczi 2022-04-28 10:11:20 UTC 
Nir Soffer has confirmed that the following patch series solves the 100% CPU consumption bug:
https://lists.gnu.org/archive/html/qemu-devel/2022-04/msg04724.html

Once the patches have been merged I'll make sure they it into the qemu-kvm RPM.
Comment 3 qing.wang 2022-05-11 08:58:14 UTC 
No issue found on 
Red Hat Enterprise Linux release 9.1 Beta (Plow)
5.14.0-86.el9.x86_64
qemu-kvm-7.0.0-2.el9.stefanha202205100940.x86_64
seabios-bin-1.16.0-1.el9.noarch
edk2-ovmf-20220221gitb24306f15d-1.el9.noarch
virtio-win-prewhql-0.1-215.iso


/usr/libexec/qemu-kvm \
  -name testvm \
  -machine q35 \
  -m  6G \
  -smp 2 \
  -cpu host,+kvm_pv_unhalt \
  -device ich9-usb-ehci1,id=usb1 \
  -device usb-tablet,id=usb-tablet1,bus=usb1.0,port=1 \
   \
   \
  -device pcie-root-port,id=pcie-root-port-0,multifunction=on,bus=pcie.0,addr=0x3,chassis=1 \
  -device pcie-root-port,id=pcie-root-port-1,port=0x1,addr=0x3.0x1,bus=pcie.0,chassis=2 \
  -device pcie-root-port,id=pcie-root-port-2,port=0x2,addr=0x3.0x2,bus=pcie.0,chassis=3 \
  -device pcie-root-port,id=pcie-root-port-3,port=0x3,addr=0x3.0x3,bus=pcie.0,chassis=4 \
  -device pcie-root-port,id=pcie-root-port-4,port=0x4,addr=0x3.0x4,bus=pcie.0,chassis=5 \
  -device pcie-root-port,id=pcie-root-port-5,port=0x5,addr=0x3.0x5,bus=pcie.0,chassis=6 \
  -device pcie-root-port,id=pcie-root-port-6,port=0x6,addr=0x3.0x6,bus=pcie.0,chassis=7 \
  -device pcie-root-port,id=pcie-root-port-7,port=0x7,addr=0x3.0x7,bus=pcie.0,chassis=8 \
  -device pcie-root-port,id=pcie_extra_root_port_0,bus=pcie.0,addr=0x4  \
  -object iothread,id=iothread0 \
  -object iothread,id=iothread1 \
  -object iothread,id=iothread2 \
  -device virtio-scsi-pci,id=scsi0,bus=pcie-root-port-4,iothread=iothread0 \
  -device virtio-scsi-pci,id=scsi1,bus=pcie-root-port-5,iothread=iothread0 \
  -device virtio-scsi-pci,id=scsi2,bus=pcie-root-port-6,iothread=iothread0 \
  -blockdev driver=qcow2,file.driver=file,cache.direct=off,cache.no-flush=on,file.filename=/home/kvm_autotest_root/images/rhel900-64-virtio-scsi.qcow2,node-name=drive_image1   \
  -device scsi-hd,id=os,drive=drive_image1,bus=scsi0.0,bootindex=0,serial=OS_DISK   \
  \
  -blockdev driver=qcow2,file.driver=file,file.filename=/home/kvm_autotest_root/images/stg1.qcow2,node-name=data_image1   \
  -device scsi-hd,id=data1,drive=data_image1,bus=scsi1.0,bootindex=1,serial=DATA_DISK1   \
  -blockdev driver=qcow2,file.driver=file,file.filename=/home/kvm_autotest_root/images/stg2.qcow2,node-name=data_image2   \
  -device scsi-hd,id=data2,drive=data_image2,bus=scsi2.0,bootindex=2,serial=DATA_DISK2  \
  -vnc :5 \
  -monitor stdio \
  -qmp tcp:0:5955,server=on,wait=off \
  -device virtio-net-pci,mac=9a:b5:b6:b1:b2:b7,id=nic1,netdev=nicpci,bus=pcie-root-port-7 \
  -netdev tap,id=nicpci \
  -chardev socket,id=qmpmonitor1,path=/var/tmp/run-qmp.log,server=on,wait=off \
  -mon chardev=qmpmonitor1,mode=control \
  -chardev socket,id=hmpmonitor1,path=/var/tmp/run-hmp.log,server=on,wait=off \
  -mon chardev=hmpmonitor1,mode=readline \
  -chardev socket,id=charserial1,path=/var/tmp/run-serial.log,server=on,wait=off \
  -device isa-serial,chardev=charserial1,id=serial1 \
  -chardev file,path=/var/tmp/run-seabios.log,id=charseabios1 \
  -device isa-debugcon,chardev=charseabios1,iobase=0x402 \
  -D debug.log \
  -boot menu=on,reboot-timeout=1000,strict=off \

The guest may boot and cpu consumption is normal
top -d1 -n5|grep qemu|awk '{print $10}'
12.0
3.0