Regression in vga performance between 0.11.1 and 0.12.1.1

Regression in vga performance between 0.11.1 and 0.12.1.1

[Adam Greenblatt]

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

Re: Regression in vga performance between 0.11.1 and 0.12.1.1

[Avi Kivity]

On 04/28/2010 10:33 PM, Adam Greenblatt wrote:
> 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.


Please post kvm_stat output for the fast and slow cases (preferably 
running the same workload, perhaps a web page displaying an animation).

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

Re: Regression in vga performance between 0.11.1 and 0.12.1.1

[Adam Greenblatt]

Avi,
   Sure -- you can download a tarball of kvm_stat logfiles from:

http://misc.cyclecounters.org/qemu-logs.tgz

I ran three workloads (a short, medium, and long) against both
0.11.1 and 0.12.3.  Each workload was started with:

time ~/qemu-0.12.3/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-9.10/0008.img

(or ~/qemu-0.11.1/bin/... and the same options.)

For the "short" workload, I just shut down the Ubuntu guest immediately 
after
it finishes logging me in.

For the "medium" workload, I open up an 80x43 terminal window in the guest,
and execute:

yes 1234567890123456789012345678901234567890 | head -n 10000

before shutting down the guest.  For the "long" workload, I open up the
same terminal window and execute:

yes 1234567890123456789012345678901234567890 | head -n 100000

before shutting down the guest.

When running these workloads under 0.12.3, you can watch the screen redraw;
it takes 1 or 2 seconds just to put up the desktop background after the 
splash screen.
Top shows the `VKoala' process as pegging one or more cpus, while the host's
X server is essentially idle (< 5% of a cpu).

When running these workloads under 0.11.1, the screen redraw is too fast to
notice -- it appears to just "blink" up instantly.  Top shows the `VKoala'
process as pegging one or more cpus during boot.  When the terminal is busy,
top shows `VKoala' and the host's X server both using ~60% of a cpu -- 
so the
guest is probably being somewhat limited by the host's wimpy graphics.

Hope this is the info you needed.  Thanks for your help!  Aloha,
   Adam

Avi Kivity wrote:
> On 04/28/2010 10:33 PM, Adam Greenblatt wrote:
>> 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.
>
>
> Please post kvm_stat output for the fast and slow cases (preferably 
> running the same workload, perhaps a web page displaying an animation).
>

Re: Regression in vga performance between 0.11.1 and 0.12.1.1

[Avi Kivity]

On 05/01/2010 10:17 PM, Adam Greenblatt wrote:
> Avi,
>   Sure -- you can download a tarball of kvm_stat logfiles from:
>

Please don't top-post.

> http://misc.cyclecounters.org/qemu-logs.tgz
>
> I ran three workloads (a short, medium, and long) against both
> 0.11.1 and 0.12.3.  Each workload was started with:
>
> time ~/qemu-0.12.3/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-9.10/0008.img
>
> (or ~/qemu-0.11.1/bin/... and the same options.)
>
> For the "short" workload, I just shut down the Ubuntu guest 
> immediately after
> it finishes logging me in.
>
> For the "medium" workload, I open up an 80x43 terminal window in the 
> guest,
> and execute:
>
> yes 1234567890123456789012345678901234567890 | head -n 10000
>
> before shutting down the guest.  For the "long" workload, I open up the
> same terminal window and execute:
>
> yes 1234567890123456789012345678901234567890 | head -n 100000
>
> before shutting down the guest.
>
> When running these workloads under 0.12.3, you can watch the screen 
> redraw;
> it takes 1 or 2 seconds just to put up the desktop background after 
> the splash screen.
> Top shows the `VKoala' process as pegging one or more cpus, while the 
> host's
> X server is essentially idle (< 5% of a cpu).
>
> When running these workloads under 0.11.1, the screen redraw is too 
> fast to
> notice -- it appears to just "blink" up instantly.  Top shows the 
> `VKoala'
> process as pegging one or more cpus during boot.  When the terminal is 
> busy,
> top shows `VKoala' and the host's X server both using ~60% of a cpu -- 
> so the
> guest is probably being somewhat limited by the host's wimpy graphics.


Anthony, can this be due to the SDL changes doing bitblt using X?

Looks like this regresses not only for remote displays, but also for 
local ones.

>
> Hope this is the info you needed.  Thanks for your help!  Aloha,
>   Adam
>
> Avi Kivity wrote:
>> On 04/28/2010 10:33 PM, Adam Greenblatt wrote:
>>> 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.
>>
>>
>> Please post kvm_stat output for the fast and slow cases (preferably 
>> running the same workload, perhaps a web page displaying an animation).
>>
> -- 
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-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.