[Bug 1879425] Re: The thread of "CPU 0 /KVM" keeping 99.9%CPU

[cliff chen]

Got it!
BTW, you can confirm this is bug for qemu-kvm, right?
 
thank you!
Cliff

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https://bugs.launchpad.net/bugs/1879425

Title:
  The thread of "CPU 0 /KVM" keeping 99.9%CPU

Status in QEMU:
  Incomplete

Bug description:
  Hi Expert:

  The VM is hung here after (2, or 3, or 5 and the longest time is 10 hours) by 
qemu-kvm.
  Notes:
  for VM:
    OS: RHEL8.1
    CPU: 1
    MEM:4G
  For qemu-kvm(host kernel RHEL7):
    1) version:
       /usr/libexec/qemu-kvm -version
       QEMU emulator version 2.10.0(qemu-kvm-ev-2.10.0-21.el7_5.4.1)
    2) once the issue is occurred, the CPU of "CPU0 /KVM" is more than 99% by 
com "top -p VM_pro_ID"
      PID  UDER   PR NI RES   S  % CPU %MEM  TIME+    COMMAND
  872067   qemu   20 0  1.6g  R   99.9  0.6  37:08.87 CPU 0/KVM
    3) use "pstack 493307" and below is function trace
  Thread 1 (Thread 0x7f2572e73040 (LWP 872067)):
  #0  0x00007f256cad8fcf in ppoll () from /lib64/libc.so.6
  #1  0x000055ff34bdf4a9 in qemu_poll_ns ()
  #2  0x000055ff34be02a8 in main_loop_wait ()
  #3  0x000055ff348bfb1a in main ()
    4) use strace "strace -tt -ff -p 872067 -o cfx" and below log keep printing
  21:24:02.977833 ppoll([{fd=4, events=POLLIN}, {fd=6, events=POLLIN}, {fd=8, 
events=POLLIN}, {fd=9, events=POLLIN}, {fd=80, events=POLLIN}, {fd=82, 
events=POLLIN}, {fd=84, events=POLLIN}, {fd=115, events=POLLIN}, {fd=121, 
events=POLLIN}], 9, {0, 0}, NULL, 8) = 0 (Timeout)
  21:24:02.977918 ppoll([{fd=4, events=POLLIN}, {fd=6, events=POLLIN}, {fd=8, 
events=POLLIN}, {fd=9, events=POLLIN}, {fd=80, events=POLLIN}, {fd=82, 
events=POLLIN}, {fd=84, events=POLLIN}, {fd=115, events=POLLIN}, {fd=121, 
events=POLLIN}], 9, {0, 911447}, NULL, 8) = 0 (Timeout)
  21:24:02.978945 ppoll([{fd=4, events=POLLIN}, {fd=6, events=POLLIN}, {fd=8, 
events=POLLIN}, {fd=9, events=POLLIN}, {fd=80, events=POLLIN}, {fd=82, 
events=POLLIN}, {fd=84, events=POLLIN}, {fd=115, events=POLLIN}, {fd=121, 
events=POLLIN}], 9, {0, 0}, NULL, 8) = 0 (Timeout)
  Therefore, I think the thread "CPU 0/KVM" is in tight loop.
    5) use reset can recover this issue. however, it will reoccurred again.
  Current work around is increase one CPU for this VM, then issue is gone.

  thanks
  Cliff

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