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Re: [Qemu-devel] qvm86, kqemu and video speed

From: use . reply-to . address
Subject: Re: [Qemu-devel] qvm86, kqemu and video speed
Date: Tue, 12 Apr 2005 23:57:55 -0400
User-agent: Mozilla Thunderbird 1.0 (Windows/20041206)

Fabrice Bellard wrote:

You can do that, but there is also a lot of optimisation opportunities in the existing Cirrus driver. My feeling is that using a driver for a virtual card will add only marginal gains (except in 3d) for a bigger amount of work (you need specific drivers in the guest OSes).

For example, in the Cirrus driver, it could be possible for the virtual CPU to access the virtual frame buffer (currently a callback is always used). A specific virtual CPU support is needed to change dynamically the type of a physical memory mapping - that's why I did not implement it when I enhanced the Cirrus driver. It will be even more critical soon with a more optimized version of kqemu.

Moreover, it could be possible to suppress one memcpy from the virtual frame buffer to the SDL/X11 frame buffer, and another memcpy if full screen mode is used (in this case, the virtual CPU accesses directly the host frame buffer).

Finally, the Cirrus bitblt operations could be redirected to the corresponding X11 DGA operations in full screen mode.

If you want to do 3d, emulating a SiS or Intel VGA card could suffice too as they are documented. I believe most of their 3d operations can be directly remapped to host OpenGL calls.

Another project would be to write a driver to use the host card in full screen mode. The QEMU support would depend on the host VGA card, but supporting only one type of card in the beginning (for example ATI Radeon cards) would suffice. The QEMU driver would swap the VGA memory frame buffer and the mmio registers when switching between the host and guest displays. It would need to do a host PCI probe to find the host VGA memory areas. Note that I think such a project should be separated from the generic host PCI card usage for which patches already exist. Supporting host PCI VGA cards need specific quirks and there is little gain in merging the two features.


this is just a suggestion , but what about 3dfx voodoo 3 cards ? they have descent implementation of opengl , probably more complete than sis , intel or via , and better understood than nvidia tnt/geforce or ati rage/radeon

they are very well supported with all MS oses and linux (native oss linux opengl-capable voodoo3 drivers are part of xfree86)

and they also supported the early 3d platform like powerVR so if someday someone want to emulate that, the guest drivers will already support it also I guess they were compatible with the dos games that supported 3dfx card natively (back in those day 3dfx was like soundblaster for sound so some games your choices are software opengl or 3dfx only , that would make the voodoo3 a very versatile platform for running pretty much any 3d software pre-2001)

also , I noticed you can have up to 6 network cards emulated , could it be possible to emulate multiple video cards too ? that way you could have 2 or more sdl or vnc screens , just like a real multi-head system

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