Re: kvm-84 -- Cirrus video updates bad on XP

Re: kvm-84 -- Cirrus video updates bad on XP

[Duck]

Patchy video updates also seems to happen, though less obviously, with 
'-vga std'.

For example, I started an XP guest with 'vga std' and then forgot about it 
for some time. When I next looked at it, the screen saver had kicked in 
(the jumping "Windows" logo) but only the bottom half of the logo was 
visible as it bounced around.

Host is Linux 2.6.27.7 with kvm drivers built from the kvm-84 source tree. 
Guest is XP0.

Haven't seen this behaviour with kvm-83.

Re: kvm-84 -- Cirrus video updates bad on XP

[Brian Kress]

    Two seperate problems.   The Cirrus VGA issue is due to it trying to 
be clever about video to video copies, which is why you see it during 
scrolling and window dragging.  I posted patch that (sort of) fixes it, 
but doesn't completely.   This whole area of code is doing something 
very iffy and getting it to do it correctly seems very hard.

    The std vga issue is because when the framebuffer is 32 bits (std 
vga is 32, cirrus vga is 24), the vga driver ends up sharing the vram 
framebuffer with the display surface.  This is interesting and means 
less copying, however it doesn't seem to be safe, as you end up with the 
display driver reading memory out of vram and the same time as the guest 
is writing to it.  Hence you end up with weirdness.


    -Brian



Duck wrote:
> Patchy video updates also seems to happen, though less obviously, with 
> '-vga std'.
>
> For example, I started an XP guest with 'vga std' and then forgot about it 
> for some time. When I next looked at it, the screen saver had kicked in 
> (the jumping "Windows" logo) but only the bottom half of the logo was 
> visible as it bounced around.
>
> Host is Linux 2.6.27.7 with kvm drivers built from the kvm-84 source tree. 
> Guest is XP0.
>
> Haven't seen this behaviour with kvm-83.
>
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kvm-84 -- Cirrus video updates bad on XP

[Duck]

Running an XP0 guest under kvm-84 with Cirrus VGA, screen updates (notably 
when copying regions of windows around during scrolling) are delayed or 
lost, so that indivudual window contents are occasionally illegible. After 
waiting a while, or moving the mouse around over the window, the updates 
seem to "catch up" and order is restored.

Reverting to kvm-83 removes this behaviour.

I notice quite a few changes to the QEMU VGA interals from -83 to -84,
inluding in the Cirrus-specific bitblitting code.

Any ideas?

XP2 with '-vga std' seems to be fine. So does X on Linux with the cirrus 
driver.