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

[Gonglei (Arei)]

> -----Original Message-----
> From: Anthony Liguori [mailto:address@hidden
> Sent: Friday, July 26, 2013 10:09 AM
> To: Gonglei (Arei)
> Cc: address@hidden; address@hidden; Hanweidong;
> Luonengjun; Huangweidong (Hardware)
> Subject: Re: [Qemu-devel] Cirrus VGA slow screen update, show blank screen
> last 13s or so for windows XP guest
> 
> Windows XP uses VGA planar mode during boot up.   This means that to
> set a pixel requires 3 MMIO operations (one for the red pixel, one for
> the green pixel, one for the blue pixel).  KVM has an optimization
> called MMIO coalescing which avoids a heavy weight exit for planar
> mode exits.  I guess Xen doesn't have an optimization like this.
> 
> Regards,
> 
> Anthony Liguori

Thanks, Anthony.
I tested the Windows XP guest again on KVM and XEN, and I found:
1. Windows XP will show blank screen during boot up as the same as 
 the protocol switch between VNC and RDP.
2. Standard VGA works well, what's difference between cirrus and standard VGA 
for the guest?
3. Why does the traditional qemu has no blank screen problem on cirrus VGA 
emulation ?

Eagerly looking forward to your reply!

-Gonglei