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 12:19, schrieb Gerd Hoffmann:
> On 07/26/13 12:02, Andreas Färber wrote:
>> 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.
> 
> 0.14 != 1.4 ;)

Oops! In that case, Gonglei, try to reproduce the issue with upstream
0.10 and use git-bisect to find out when things got slower between
v0.10.2..v0.14.0. It would be unrealistic to expect us to remember all
Cirrus-related changes from 2-4 years ago. ;)

Andreas

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