[fedora-virt] Different cpu usage between Fedora and SL6 guests

[Orion Poplawski]

On 07/17/2012 05:16 PM, Eric Blake wrote:
> On 07/17/2012 04:50 PM, Orion Poplawski wrote:
>> While staring at top on my SL6 kvm server waiting for it to crash, I
>> noticed that my idle Fedora kvm guests appear to be consuming between
>> 8-12% cpu while my idle SL6 guests appear to be consuming between 0.3-2%
>> cpu as shown in the qemu-kvm processes in top.  In fact I have a Fedora
>> 17 instance running now with nothing but kernel processes and the
>> qemu-kvm process still shows it using 7-8% cpu.
>>
>> Does anyone have any insight as to why this would be the case?
>
> Could it be an issue of vnc vs. spice?  It may help if you provide the
> 'virsh dumpxml $dom' of the two guests in question, to point out if any
> difference in configuration may be responsible.  Also bear in mind that
> the virt stack strives for guest ABI compatibility - so a guest created
> 2 years ago will still use the defaults from 2 years ago, even if the
> defaults have since improved in the meantime for a guest created today.
>   You can rewrite the XML, generally with no ill effects to a Linux
> guest, but at risk of having to revalidate a Windows guest (hence why
> the virt stack strives for stable ABI instead of auto-rewriting your
> guests to use latest-and-greatest defaults).
>

Using VNC for all.  There is very little difference in the configuration.  For 
one example (drupal is SL6, mock1 is Fedora 17):

diff drupal.xml mock1.xml
1,6c1,6
< <domain type='kvm' id='1'>
<   <name>drupal</name>
<   <uuid>bfdc6b27-396d-83d7-0c91-8e610aa3a40d</uuid>
<   <memory unit='KiB'>524288</memory>
<   <currentMemory unit='KiB'>524288</currentMemory>
<   <vcpu placement='static'>1</vcpu>
---
 > <domain type='kvm' id='6'>
 >   <name>mock1</name>
 >   <uuid>bf102e31-36c5-d9bf-9000-29293e927fef</uuid>
 >   <memory unit='KiB'>2097152</memory>
 >   <currentMemory unit='KiB'>2097152</currentMemory>
 >   <vcpu placement='static'>4</vcpu>
8c8
<     <type arch='x86_64' machine='rhel6.2.0'>hvm</type>
---
 >     <type arch='x86_64' machine='rhel6.1.0'>hvm</type>
24c24
<       <source dev='/dev/vg_root/vm_drupal'/>
---
 >       <source dev='/dev/vg_root/vm_mock1'/>
34c34
<       <mac address='40:00:00:00:00:10'/>
---
 >       <mac address='40:00:00:00:00:11'/>
36c36
<       <target dev='vnet0'/>
---
 >       <target dev='vnet2'/>
42c42
<       <source path='/dev/pts/1'/>
---
 >       <source path='/dev/pts/8'/>
46,47c46,47
<     <console type='pty' tty='/dev/pts/1'>
<       <source path='/dev/pts/1'/>
---
 >     <console type='pty' tty='/dev/pts/8'>
 >       <source path='/dev/pts/8'/>
55c55
<     <graphics type='vnc' port='5900' autoport='yes' keymap='en-us'/>
---
 >     <graphics type='vnc' port='5902' autoport='yes' keymap='en-us'/>
67,68c67,68
<     <label>system_u:system_r:svirt_t:s0:c288,c830</label>
<     <imagelabel>system_u:object_r:svirt_image_t:s0:c288,c830</imagelabel>
---
 >     <label>system_u:system_r:svirt_t:s0:c129,c713</label>
 >     <imagelabel>system_u:object_r:svirt_image_t:s0:c129,c713</imagelabel>

All my other domains are "rhel6.1.0" and the SL6 one is fine.

At this point I would have to think it is differences in the guest kernels. 
Not sure what the best way of tracing what the qmeu-kvm process is doing and 
comparing them.

-- 
Orion Poplawski
Technical Manager                     303-415-9701 x222
NWRA, Boulder Office                  FAX: 303-415-9702
3380 Mitchell Lane                       orion at nwra.com
Boulder, CO 80301                   http://www.nwra.com