On 07/26/13 12:02, Andreas Färber wrote: > Am 26.07.2013 08:41, schrieb Gonglei (Arei): >>> -----Original Message----- >>> From: Anthony Liguori [mailto:anth...@codemonkey.ws] >>> Sent: Friday, July 26, 2013 11:21 AM >>> To: Gonglei (Arei) >>> Cc: qemu-devel@nongnu.org; xen-de...@lists.xen.org; Hanweidong; >>> Luonengjun; Huangweidong (Hardware) >>> Subject: Re: [Qemu-devel] Cirrus VGA slow screen update, show blank screen >>> last 13s or so for windows XP guest >>> >>> On Thu, Jul 25, 2013 at 10:08 PM, Gonglei (Arei) >>> <arei.gong...@huawei.com> wrote: >>>> 3. Why does the traditional qemu has no blank screen problem on cirrus VGA >>> emulation ? >>> >>> This is one of the few cases where TCG is actually faster than KVM or >>> Xen. In TCG, an MMIO exit is converted to a function call. OTOH, >>> even with KVM, an MMIO exit is at least a couples thousand cycles. >>> It's worse with Xen because dom0 has to be scheduled. >> >> Perhaps I did not express clearly what I mean at #3. >> I don't understand why the qemu-dm(qemu-0.10.2) works well >> but the upstream qemu(begin with qemu-0.14) is not for the >> same windows XP guest image in cirrus vga emulation. Does >> the cirrus vga emulation have some differences between >> qemu-dm and unstream qemu ? > > I don't know about qemu-dm, but QEMU switched from a home-grown pixel > handling to pixman library sometime around 1.4. CC'ing Gerd.
0.14 != 1.4 ;) Also pixman isn't used everywhere, there is still home-grown pixel handling code in qemu. I often replace it when I touch it for some reason, but we are far away from a full-pixman qemu. The cirrus blit ops havn't been touched btw, it's still the old code. Maybe the xen guys did some optimizations in qemu-dm which where not merged upstream. Try asking @ xen-devel. Beside that the standard vga usually is the better choice anyway as it supports more video memory and higher resolutions than cirrus. cheers, Gerd
