[Qemu-devel] [Bug 1794285] [NEW] 100% Host CPU usage while guest idling

[Gareth Bryan]

Public bug reported:

Hi,

We have an appliance that runs a FreeBSD guest on a Yocto-based host via 
qemu-system-x86_64.
Everything functions fine however the host uses n00% of the CPU (where n = 
#smp) and RAM allocated to it whilst the 1 guest is sat nearing idle.

Host:
PID     USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
4406    root      20   0 16.7g  16g  26m S  500 53.0  17958:38 qemu-system-x86

Guest:
CPU 0:  0.0% user,  0.0% nice,  0.4% system,  0.0% interrupt, 99.6% idle
CPU 1:  0.0% user,  0.0% nice,  0.4% system,  0.0% interrupt, 99.6% idle
CPU 2:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU 3:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
CPU 4:  0.4% user,  0.0% nice,  0.0% system,  0.0% interrupt, 99.6% idle
Mem: 43M Active, 4783M Inact, 1530M Wired, 911M Buf, 9553M Free
Swap: 3072M Total, 3072M Free

I have logged this with the appliance vendor and received the response:
"This is expected behaviour and you will see the same in any case where a Guest 
OS runs over a Host OS.
Host here has 5 CPUs and it has assigned all of them to Guest. 
Since the Host is not being shared by any Guest OS; you will always see the 
500% (or the 5 CPUs) given to qemu-system-x86.
I do see the same in lab and is very much expected"

This feels fundamentally wrong to me.
I'm somewhat limited by what can be tested due to the nature of this being an 
appliance rather than a mainstream distro.

I'm looking for feedback that I can use to push the vendor into
investigating this issue.

Versions below.

Many thanks,
Gareth


Host:
Linux 204a-node 3.10.100-ovp-rt110-WR6.0.0.31_preempt-rt #1 SMP Fri
Aug 3 01:59:01 PDT 2018 x86_64 x86_64 x86_64 GNU/Linux

Qemu:
QEMU emulator version 1.7.2, Copyright (c) 2003-2008 Fabrice Bellard

Command:
(Vendor identifying information has been removed)

/usr/bin/qemu-system-x86_64 \
-name REMOVED \
-S \
-machine pc-i440fx-1.7,accel=kvm,usb=off \
-m 16384 \
-realtime mlock=on \
-smp 5,sockets=5,cores=1,threads=1 \
-uuid 76277b29-3bd4-4dd4-a705-ed34d6449d6d \
-nographic \
-no-user-config \
-nodefaults \
-chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/REMOVED.monitor,server,nowait \
-mon chardev=charmonitor,id=monitor,mode=control \
-rtc base=utc \
-no-shutdown \
-boot strict=on \
-device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 \
-device virtio-scsi-pci,id=scsi0,bus=pci.0,addr=0x17 \
-netdev tap,fd=22,id=hostnet0,vhost=on,vhostfd=23 \
-device virtio-net-pci,netdev=hostnet0,id=net0,mac=REMOVED,bus=pci.0,addr=0x11 \
-netdev 
tap,ifname=tap1,script=/etc/vehostd/XXX-em3-ifup,id=hostnet1,vhost=on,vhostfd=24
 \
-device virtio-net-pci,netdev=hostnet1,id=net1,mac=REMOVED,bus=pci.0,addr=0x12 \
-netdev 
tap,ifname=tap2,script=/etc/vehostd/REMOVED-em4-ifup-SUMMIT,id=hostnet2,vhost=on,vhostfd=25
 \
-device virtio-net-pci,netdev=hostnet2,id=net2,mac=REMOVED,bus=pci.0,addr=0x1c \
-netdev 
tap,ifname=tap3,script=/etc/vehostd/REMOVED-em4-re-re-ifup,id=hostnet3,vhost=on,vhostfd=26
 \
-device virtio-net-pci,netdev=hostnet3,id=net3,mac=REMOVED,bus=pci.0,addr=0x1d \
-chardev pty,id=charserial0 \
-device isa-serial,chardev=charserial0,id=serial0 \
-chardev tty,id=charserial1,path=/dev/ttyS1 \
-device isa-serial,chardev=charserial1,id=serial1 \
-chardev tty,id=charserial2,path=/dev/ttyS2 \
-device isa-serial,chardev=charserial2,id=serial2 \
-chardev tty,id=charserial3,path=/dev/ttyS3 \
-device isa-serial,chardev=charserial3,id=serial3 \
-device i6300esb,id=watchdog0,bus=pci.0,addr=0x10 \
-watchdog-action reset \
-object rng-random,id=rng0,filename=/dev/random \
-device virtio-rng-pci,rng=rng0,max-bytes=1024,period=2000,bus=pci.0,addr=0x1e \
-smbios type=0,vendor="INSYDE 
Corp.",version=REMOVED,date=11/03/2017,release=1.00 \
-smbios 
type=1,manufacturer=REMOVED,product=REMOVED,version=REMOVED,serial=VF-NET \
-device REMOVED-pci,host=0000:1c:00.0 \
-device kvm-pci-assign,host=0000:00:14.0 \
-device pci-hgcommdev,vmindex=0,bus=pci.0,addr=0x16 \
-drive 
file=/REMOVED/REMOVED-current.img,if=none,id=drive-virtio-disk0,format=raw,cache=directsync,aio=native
 \
-device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x13,drive=drive-virtio-disk0,id=virtio-disk0,config-wce=off,x-data-plane=on,bootindex=1
 \
-drive 
file=/REMOVED/REMOVED-var-config.img,if=none,id=drive-virtio-disk1,format=raw,cache=directsync,aio=native
 \
-device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x15,drive=drive-virtio-disk1,id=virtio-disk1,config-wce=off,x-data-plane=on,bootindex=-1
 \
-drive 
file=/REMOVED/REMOVED-aux-disk.img,if=none,id=drive-ide0-0-1,format=raw,cache=directsync,discard=unmap
 \
-device ide-hd,bus=ide.0,unit=1,drive=drive-ide0-0-1,id=ide0-0-1,bootindex=-1 \
-drive 
file=/REMOVED/images/0/REMOVED-platform.img,if=none,id=drive-ide1-0-1,format=raw,cache=directsync,discard=unmap
 \
-device ide-hd,bus=ide.1,unit=1,drive=drive-ide1-0-1,id=ide1-0-1,bootindex=-1 \
-msg timestamp=on

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1794285

Title:
  100% Host CPU usage while guest idling

Status in QEMU:
  New

Bug description:
  Hi,

  We have an appliance that runs a FreeBSD guest on a Yocto-based host via 
qemu-system-x86_64.
  Everything functions fine however the host uses n00% of the CPU (where n = 
#smp) and RAM allocated to it whilst the 1 guest is sat nearing idle.

  Host:
  PID     USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
  4406    root      20   0 16.7g  16g  26m S  500 53.0  17958:38 qemu-system-x86

  Guest:
  CPU 0:  0.0% user,  0.0% nice,  0.4% system,  0.0% interrupt, 99.6% idle
  CPU 1:  0.0% user,  0.0% nice,  0.4% system,  0.0% interrupt, 99.6% idle
  CPU 2:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
  CPU 3:  0.0% user,  0.0% nice,  0.0% system,  0.0% interrupt,  100% idle
  CPU 4:  0.4% user,  0.0% nice,  0.0% system,  0.0% interrupt, 99.6% idle
  Mem: 43M Active, 4783M Inact, 1530M Wired, 911M Buf, 9553M Free
  Swap: 3072M Total, 3072M Free

  I have logged this with the appliance vendor and received the response:
  "This is expected behaviour and you will see the same in any case where a 
Guest OS runs over a Host OS.
  Host here has 5 CPUs and it has assigned all of them to Guest. 
  Since the Host is not being shared by any Guest OS; you will always see the 
500% (or the 5 CPUs) given to qemu-system-x86.
  I do see the same in lab and is very much expected"

  This feels fundamentally wrong to me.
  I'm somewhat limited by what can be tested due to the nature of this being an 
appliance rather than a mainstream distro.

  I'm looking for feedback that I can use to push the vendor into
  investigating this issue.

  Versions below.

  Many thanks,
  Gareth


  Host:
  Linux 204a-node 3.10.100-ovp-rt110-WR6.0.0.31_preempt-rt #1 SMP Fri
  Aug 3 01:59:01 PDT 2018 x86_64 x86_64 x86_64 GNU/Linux

  Qemu:
  QEMU emulator version 1.7.2, Copyright (c) 2003-2008 Fabrice Bellard

  Command:
  (Vendor identifying information has been removed)

  /usr/bin/qemu-system-x86_64 \
  -name REMOVED \
  -S \
  -machine pc-i440fx-1.7,accel=kvm,usb=off \
  -m 16384 \
  -realtime mlock=on \
  -smp 5,sockets=5,cores=1,threads=1 \
  -uuid 76277b29-3bd4-4dd4-a705-ed34d6449d6d \
  -nographic \
  -no-user-config \
  -nodefaults \
  -chardev 
socket,id=charmonitor,path=/var/lib/libvirt/qemu/REMOVED.monitor,server,nowait \
  -mon chardev=charmonitor,id=monitor,mode=control \
  -rtc base=utc \
  -no-shutdown \
  -boot strict=on \
  -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 \
  -device virtio-scsi-pci,id=scsi0,bus=pci.0,addr=0x17 \
  -netdev tap,fd=22,id=hostnet0,vhost=on,vhostfd=23 \
  -device 
virtio-net-pci,netdev=hostnet0,id=net0,mac=REMOVED,bus=pci.0,addr=0x11 \
  -netdev 
tap,ifname=tap1,script=/etc/vehostd/XXX-em3-ifup,id=hostnet1,vhost=on,vhostfd=24
 \
  -device 
virtio-net-pci,netdev=hostnet1,id=net1,mac=REMOVED,bus=pci.0,addr=0x12 \
  -netdev 
tap,ifname=tap2,script=/etc/vehostd/REMOVED-em4-ifup-SUMMIT,id=hostnet2,vhost=on,vhostfd=25
 \
  -device 
virtio-net-pci,netdev=hostnet2,id=net2,mac=REMOVED,bus=pci.0,addr=0x1c \
  -netdev 
tap,ifname=tap3,script=/etc/vehostd/REMOVED-em4-re-re-ifup,id=hostnet3,vhost=on,vhostfd=26
 \
  -device 
virtio-net-pci,netdev=hostnet3,id=net3,mac=REMOVED,bus=pci.0,addr=0x1d \
  -chardev pty,id=charserial0 \
  -device isa-serial,chardev=charserial0,id=serial0 \
  -chardev tty,id=charserial1,path=/dev/ttyS1 \
  -device isa-serial,chardev=charserial1,id=serial1 \
  -chardev tty,id=charserial2,path=/dev/ttyS2 \
  -device isa-serial,chardev=charserial2,id=serial2 \
  -chardev tty,id=charserial3,path=/dev/ttyS3 \
  -device isa-serial,chardev=charserial3,id=serial3 \
  -device i6300esb,id=watchdog0,bus=pci.0,addr=0x10 \
  -watchdog-action reset \
  -object rng-random,id=rng0,filename=/dev/random \
  -device 
virtio-rng-pci,rng=rng0,max-bytes=1024,period=2000,bus=pci.0,addr=0x1e \
  -smbios type=0,vendor="INSYDE 
Corp.",version=REMOVED,date=11/03/2017,release=1.00 \
  -smbios 
type=1,manufacturer=REMOVED,product=REMOVED,version=REMOVED,serial=VF-NET \
  -device REMOVED-pci,host=0000:1c:00.0 \
  -device kvm-pci-assign,host=0000:00:14.0 \
  -device pci-hgcommdev,vmindex=0,bus=pci.0,addr=0x16 \
  -drive 
file=/REMOVED/REMOVED-current.img,if=none,id=drive-virtio-disk0,format=raw,cache=directsync,aio=native
 \
  -device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x13,drive=drive-virtio-disk0,id=virtio-disk0,config-wce=off,x-data-plane=on,bootindex=1
 \
  -drive 
file=/REMOVED/REMOVED-var-config.img,if=none,id=drive-virtio-disk1,format=raw,cache=directsync,aio=native
 \
  -device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0x15,drive=drive-virtio-disk1,id=virtio-disk1,config-wce=off,x-data-plane=on,bootindex=-1
 \
  -drive 
file=/REMOVED/REMOVED-aux-disk.img,if=none,id=drive-ide0-0-1,format=raw,cache=directsync,discard=unmap
 \
  -device ide-hd,bus=ide.0,unit=1,drive=drive-ide0-0-1,id=ide0-0-1,bootindex=-1 
\
  -drive 
file=/REMOVED/images/0/REMOVED-platform.img,if=none,id=drive-ide1-0-1,format=raw,cache=directsync,discard=unmap
 \
  -device ide-hd,bus=ide.1,unit=1,drive=drive-ide1-0-1,id=ide1-0-1,bootindex=-1 
\
  -msg timestamp=on

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