[Qemu-devel] text updates slow after commit 7d957bd8cbcbf56f7916d375e65042d767f544b5

[Qemu-devel] text updates slow after commit 7d957bd8cbcbf56f7916d375e65042d767f544b5

[Chris Frey]

Hi,

I was using an older devel tree, and decided it was time to try out
the new stable 0.10.2.

Unfortunately, I'm finding that screen updates, when the guest is in
text mode (such as the grub boot screen), are extremely slow.  I can see
the text update as if it was a 28.8k modem. :-)

A git bisect showed that the slowness was introduced at git commit
7d957bd8cbcbf56f7916d375e65042d767f544b5

	DisplayState interface change (Stefano Stabellini)

Can anyone offer any tips on how to speed things up again?

Thanks,
- Chris

Re: [Qemu-devel] text updates slow after commit 7d957bd8cbcbf56f7916d375e65042d767f544b5

[Anthony Liguori]

Chris Frey wrote:
> Hi,
>
> I was using an older devel tree, and decided it was time to try out
> the new stable 0.10.2.
>
> Unfortunately, I'm finding that screen updates, when the guest is in
> text mode (such as the grub boot screen), are extremely slow.  I can see
> the text update as if it was a 28.8k modem. :-)
>
> A git bisect showed that the slowness was introduced at git commit
> 7d957bd8cbcbf56f7916d375e65042d767f544b5
>
> 	DisplayState interface change (Stefano Stabellini)
>
> Can anyone offer any tips on how to speed things up again?
>   

What's your configuration (host type, etc.)?  Are you remoting over X?

Regards,

Anthony Liguori

> Thanks,
> - Chri
>
>
>
>   

[Qemu-devel] Re: text updates slow after commit 7d957bd8cbcbf56f7916d375e65042d767f544b5

[Chris Frey]

On Tue, Apr 28, 2009 at 04:40:58PM -0500, Anthony Liguori wrote:
> What's your configuration (host type, etc.)?  Are you remoting over X?

Wow, fast response. :-)

I'm running on 32bit x86, with a x86 32 bit guest.  I don't have the hardware
needed for KVM.  It's an older P4, 3Ghz.

I compiled with:

./configure --prefix=/home/cdfrey/software/qemu/git/rootdir \
	--enable-system \
	--enable-linux-user \
	--disable-kvm \
        --cc=ccache_gcc \
        --host-cc=ccache_gcc

I'm running a Debian unstable guest, upgraded from Lenny, using:

/home/cdfrey/software/qemu/git/rootdir/bin/qemu -boot c -m 256 \
	-hda debian-unstable.img -cdrom debian-500-i386-businesscard.iso \
	-net nic,vlan=0 -net user,vlan=0 -usb -usbdevice host:0fca:0004

I don't have to actually boot... I see the screen slowness from the grub
screen.

Let me know if I missed anything.

- Chris

[Qemu-devel] Re: text updates slow after commit 7d957bd8cbcbf56f7916d375e65042d767f544b5

[Chris Frey]

On Tue, Apr 28, 2009 at 04:40:58PM -0500, Anthony Liguori wrote:
> What's your configuration (host type, etc.)?  Are you remoting over X?

Oops, forgot to say that I am using X through an SSH forward.

	ssh -Y -a -2 ...

- Chris

[Qemu-devel] Re: text updates slow after commit 7d957bd8cbcbf56f7916d375e65042d767f544b5

[Anthony Liguori]

Chris Frey wrote:
> On Tue, Apr 28, 2009 at 04:40:58PM -0500, Anthony Liguori wrote:
>   
>> What's your configuration (host type, etc.)?  Are you remoting over X?
>>     
>
> Oops, forgot to say that I am using X through an SSH forward.
>
> 	ssh -Y -a -2 ...
>   

That's what I figured.  You should use -vnc instead.

In the 0.10.x series, we changed the way we interact with libsdl.  We're 
now relying on libsdl to do pixel conversion.  It appears that SDL is 
sending a lot more data to the X server when you do this than it was 
previously.  The result is a marked slowdown when remoting QEMU over X.

Fortunately, we have an integrated remoting mechanism (-vnc) that 
doesn't suffer from these problems.

If you think this really should be addressed, I'd suggest reporting it 
to the SDL community as they're the ones who are best positioned to 
detect that it's a remote X server and then do local conversion 
appropriately.  Alternatively, I suspect using an X protocol optimizer 
(like NX) would make this problem go away.

Regards,

Anthony Liguori

> - Chris
>
>