Re: [Qemu-devel] [Xen-devel] Cirrus VGA slow screen update, show blank screen last 13s or so for windows XP guest

[Fabio Fantoni]

Il 26/07/2013 03:57, Gonglei (Arei) ha scritto:
> > > > Il 25/07/2013 15:13, Gonglei (Arei) ha scritto:
> > > > > Hi,
> > > > >      I found a problem: For windows XP guest booting by qemu upstream,
> > > > > using the RDP(Remote Desktop Protocol) and VNC protocol to connect the
> > > > windows XP guest
> > > > > which booting by Qemu upstream respectively. the VNC client will become
> > > > blank screen last
> > > > > 13 seconds or so on XEN platform, and last 2 seconds on KVM. And through
> > > > debugging,
> > > > > the cirrus VGA card does not produce dirty pages during the blank screen's
> > > > times.
> > > > >      When -vga is changed from cirrus to std the issue goes away and the
> > > > update proceeds at normal speed.
> > > > > In addition, when using the Qemu-dm replace Qemu upstream on XEN
> > > > platform,
> > > > > the cirrus VGA works good and the issue goes away also.
> > > > >
> > > > >      Today, lots of googling have seen the same behavior:
> > > > >
> > > > > https://github.com/joyent/smartos-live/issues/215
> > > > > http://lists.gnu.org/archive/html/qemu-devel/2011-06/msg02105.html
> > > > > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=574988
> > > > > etc...
> > > > >
> > > > >      But, I test the latest qemu-1.5.1, the problem exist firmly.
> > > > >
> > > > >      Any ideas? Thanks!
> > > > >
> > > > > Best Regards!
> > > > > -Gonglei
> > > > > _______________________________________________
> > > > > Xen-devel mailing list
> > > > > address@hidden
> > > > > http://lists.xen.org/xen-devel
> > > > I've seen the perfomance problem too with vnc when I started to try
> > > > upstream qemu. I already reported it on the end of 2011 but no solution yet.
> > > > I found spice as an alternative: qxl vga will not work on xen until SSE
> > > > support will be added on hvm domU, but spice is usable with stdvga and
> > > > performance is better that vnc. Combined with vdagent and usb
> > > > redirection it makes a perfect vkvm, and more.
> > > > Spice basic support in xl is already present and for more features I
> > > > posted some patches here but they are not included in upstream for now.
> > > > Cirrus vga drivers are also old and have limitations on both windows and
> > > > linux and they can add other problems, they are probably not good for
> > > > recent os/de.
> > > Thanks for responding. I don't understand why the Qemu-dm works well
> > > but the upstream qemu is not for the same windows XP guest image.
> > > Does the Cirrus vga emulation have some differences between qemu-dm
> > > and unstream qemu ?
> > >
> > > -Gonglei
> > I did test on cirrus vga a long time ago, last was on videoram settings
> > patch.
> > Try to increase videoram setting to see if you see an increasing in
> > performances and/or the problem persists.
> > On my tests the performance seem identical.
> I set the videoram 8M, because of the upstream qemu will crash if the videoram
> less than 8M On the Xen prlatform, and the qemu's log show:
>
> qemu: hardware error: xen: failed to populate ram at 7fc00000
> CPU #0:
> EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000633
> ESI=00000000 EDI=00000000 EBP=00000000 ESP=00000000
> EIP=0000fff0 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
> ES =0000 00000000 0000ffff 00009300
> CS =f000 ffff0000 0000ffff 00009b00
> SS =0000 00000000 0000ffff 00009300
> DS =0000 00000000 0000ffff 00009300
> FS =0000 00000000 0000ffff 00009300
> GS =0000 00000000 0000ffff 00009300
> LDT=0000 00000000 0000ffff 00008200
> TR =0000 00000000 0000ffff 00008b00
> GDT=     00000000 0000ffff
> IDT=     00000000 0000ffff
> CR0=60000010 CR2=00000000 CR3=00000000 CR4=00000000
> DR0=00000000 DR1=00000000 DR2=00000000 DR3=0
> 0000000
> etc...

This is because xen reserve ram for video specified by videoram 
parameter but upstream qemu forces to 8 mb in any case.
This should be fixed after this patch:
http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=2e814a017155b885e4d4b5a88dc05e7367a9722a
Is included on xen 4.3 and also backported to 4.2.2.

> > Probably the causes of video problems with upstream qemu are some
> > hardcoding on xen (probably on hvmloader and fixed seabios tables).
> > I wasn't able to found exactly problem.
> Next, I will compare them.
>
> -Gonglei