[CentOS-virt] High CPU Usage

Fri Dec 7 22:19:55 UTC 2012
Dennis Jacobfeuerborn <dennisml at conversis.de>

On 12/07/2012 10:04 PM, Shawn Everett wrote:
> Hi All,
> 
> I have recently installed CentOS 6.3 with QEMU+KVM for Virtualization.
> 
>  I have successfully created a Windows 2003 VM with 4GB of RAM.  The host
>  server is an HP ML350 G8 with 24GB RAM and 24 cores.  Details of one of
>  the cores is shown below:
> 
>  processor       : 23
>  vendor_id       : GenuineIntel
>  cpu family      : 6
>  model           : 45
>  model name      : Intel(R) Xeon(R) CPU E5-2620 0 @ 2.00GHz
>  stepping        : 7
>  cpu MHz         : 1200.000
>  cache size      : 15360 KB
>  physical id     : 1
>  siblings        : 12
>  core id         : 5
>  cpu cores       : 6
>  apicid          : 43
>  initial apicid  : 43
>  fpu             : yes
>  fpu_exception   : yes
>  cpuid level     : 13
>  wp              : yes
>  flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca
>  cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx
>  pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good xtopology
>  nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2
>  ssse3 cx16 xtpr pdcm dca sse4_1 sse4_2 x2apic popcnt aes xsave avx lahf_lm
>  ida arat epb xsaveopt pln pts dts tpr_shadow vnmi flexpriority ept vpid
>  bogomips        : 3989.86
>  clflush size    : 64
>  cache_alignment : 64
>  address sizes   : 46 bits physical, 48 bits virtual
>  power management:
> 
>  On an otherwise completely idle system I've noticed the load to be 1.0 to
>  1.5 range.  Running "top" shows the culprit to be: qemu-kvm.
> 
>  Is this normal behavior?  I would have expected the load to be pretty
>  light.
> 
>  Stopping the VM restores the load to normal once again.
> 
>  Is there anything I can do to reduce the load?

You probably have 12 cores and thanks to hyper-threading that gives you 24
threads (big difference).
Have you installed the virtio drivers in the VM? That might reduce the load
a bit. Also was does running "vmstat 3" for about 20 seconds show?

Regards,
  Dennis