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

[Andreas Färber]

Am 26.07.2013 08:41, schrieb Gonglei (Arei):
>> -----Original Message-----
>> From: Anthony Liguori [mailto:address@hidden
>> Sent: Friday, July 26, 2013 11:21 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
>>
>>  On Thu, Jul 25, 2013 at 10:08 PM, Gonglei (Arei)
>> <address@hidden> 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.

(And 1.5 switched the default GUI backend from SDL to GTK, which may
again show some performance differences.)

Andreas

-- 
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg