Anthony Liguori
2013-Jul-26 02:09 UTC
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 On Thu, Jul 25, 2013 at 8:13 AM, Gonglei (Arei) <arei.gonglei@huawei.com> wrote:> 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