Regression in vga performance between 0.11.1 and 0.12.1.1

[Adam Greenblatt <adam.greenblatt@gmail.com>]

Hi,
   I noticed that certain guests (for example, Ubuntu 9.04, Ubuntu 9.10,
and the Ubuntu 10.04 release candidate) show dramatically (~100x) slower
graphical output when running under qemu-kvm-0.12.1.1 than under 
qemu-kvm-0.11.1.
Other guests, notably Windows XP and Windows Vista, run fine under both
version of qemu.  The regression is still present in qemu-kvm-0.12.3.
   Here's the information you request when submitting a bug report:

    * what cpu model (examples: Intel Core Duo, Intel Core 2 Duo, AMD 
Opteron 2210)

       The host has two Xeon X5650 cpus.

    * what kvm version you are using. If you're using git directly, 
provide the output of 'git describe'.

       I'm using the kvm included with the stock 2.6.32.12 kernel, and 
two different
       qemu-kvms: version 0.11.1, which works fine, and version 
0.12.1.1, which has
       the regression.

    * the host kernel version

       I'm running kernel 2.6.32.12 on the host.

    * what host kernel arch you are using (i386 or x86_64)

       i386.

    * what guest you are using, including OS type (Linux, Windows, 
Solaris, etc.), bitness (32 or 64), kernel version

       Guests that are affected:
          Ubuntu 9.04 - kernel 2.6.28-18, 32 bits
          Ubuntu 9.10 - kernel 2.6.31-20, 32 bits
          Ubuntu 10.04 - kernel 2.6.32-21, 32-bits
       Guests that aren't affected:
          Windows XP SP3, Windows Vista SP2: both 32 bits

    * the qemu command line you are using to start the guest

       Here's one that works:

DISPLAY=:0.2 ~/qemu0111/bin/qemu-system-x86_64 -m 1536 -soundhw es1370 
-smp 4 -usb -usbdevice tablet -vga std -cpu core2duo -snapshot -name 
"VKoala (r/o)",process="VKoala" -net nic,macaddr=DE:AD:BE:EF:00:08 -net 
tap,vlan=0,ifname=tap6,script=no,downscript=no /vm/ubuntu-9.10/0006.img

       Here's one that works, but has drastically slower graphics (the only
       change is which qemu-system-x86_64 I'm running.)

DISPLAY=:0.2 ~/qemu01211/bin/qemu-system-x86_64 -m 1536 -soundhw es1370 
-smp 4 -usb -usbdevice tablet -vga std -cpu core2duo -snapshot -name 
"VKoala (r/o)",process="VKoala" -net nic,macaddr=DE:AD:BE:EF:00:08 -net 
tap,vlan=0,ifname=tap6,script=no,downscript=no /vm/ubuntu-9.10/0006.img

       Here are two that work fine with either binary:

DISPLAY=:0.2 ~/qemu01211/bin/qemu-system-x86_64 -m 1536 -soundhw es1370 
-usb -usbdevice tablet -localtime -vga std -cpu core2duo -snapshot -name 
"VXP (r/o)",process="VXP" -net nic,macaddr=DE:AD:BE:EF:00:01 -net 
tap,vlan=0,ifname=tap0,script=no,downscript=no /vm/xp/0024.img

DISPLAY=:0.2 ~/qemu01211/bin/qemu-system-x86_64 -m 1536 -soundhw es1370 
-smp 2 -usb -usbdevice tablet -localtime -vga std -cpu core2duo 
-snapshot -name "VVista (r/o)",process="VVista" -net 
nic,macaddr=DE:AD:BE:EF:00:02 -net 
tap,vlan=0,ifname=tap1,script=no,downscript=no /vm/vista/0009.img

    * whether the problem goes away if using the -no-kvm-irqchip or 
-no-kvm-pit switch.

       Neither of these switches change the results.

    * whether the problem also appears with the -no-kvm switch.

       This switch makes everything run so much slower that I can't tell 
if it
       changes the results.

Please cc me if you have any questions, as I'm not subscribed to the kvm 
list.
Thanks for working on kvm, it's a great piece of software!  Aloha,
   Adam Greenblatt