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

[Orion Poplawski]

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?
>

  It appears that toggling the Autosuspend for USB device QEMU USB Tablet 
[QEMU 0.12.1] tunable has a big effect and brings it in line with SL6.

SL6:
usb 1-1: Product: QEMU USB Tablet
input: QEMU 0.12.1 QEMU USB Tablet as 
/devices/pci0000:00/0000:00:01.2/usb1/1-1/1-1:1.0/input/input4
generic-usb 0003:0627:0001.0001: input,hidraw0: USB HID v0.01 Pointer [QEMU 
0.12.1 QEMU USB Tablet] on usb-0000:00:01.2-1/input0

# cat /sys/devices/pci0000:00/0000:00:01.2/usb1/1-1/power/autosuspend
2
# cat  /sys/devices/pci0000:00/0000:00:01.2/usb1/1-1/power/level
auto

F17:
[    3.015642] usb 1-1: Product: QEMU USB Tablet
[    3.117125] input: QEMU 0.12.1 QEMU USB Tablet as 
/devices/pci0000:00/0000:00:01.2/usb1/1-1/1-1:1.0/input/input3
[    3.117827] generic-usb 0003:0627:0001.0001: input,hidraw0: USB HID v0.01 
Pointer [QEMU 0.12.1 QEMU USB Tablet] on usb-0000:00:01.2-1/input0

# cat /sys/devices/pci0000:00/0000:00:01.2/usb1/power/autosuspend
2
# cat  /sys/devices/pci0000:00/0000:00:01.2/usb1/1-1/power/level
on

So it appears that SL6 is setting to auto automatically, but Fedora is not.  I 
wonder why.

-- 
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