设备概念和对比
qemu支持的虚拟显卡设备类型比较多。初次接触会比较懵逼。 直到阅读大佬kraxel的文章，受益良多: VGA and other display devices in qemu
根据文章整理成表格对比：
| VGA compatible | vgabios support | UEFI support | linux driver | PCI Express slot | Remarks | |
|---|---|---|---|---|---|---|
| standard VGA | √ | √ | √ | √ | × | |
| bochs | × | √ | √ | √ | √ | |
| virtio vga | √ | √ | √ | √ | × | |
| virtio gpu | × | × | √ | √ | √ | |
| vhost-user virtio gpu | There is a vhost-user variant for both virtio vga and virtio gpu. This allows to run the virtio-gpu emulation in a separate process. | |||||
| qxl vga | √ | √ | √ | √ | × | |
| qxl | × | × | √ | √ | × | Providing multihead support for windows guests is pretty much the only use case for this device. |
| cirrus vga | √ | √ | √ | √ | × | Emulates a Cirrus SVGA device which used to be modern in the 90ies of the last century |
| ramfb | × | √ | √ | √ | × |
一些概念：
- VGA compatibility：即使guest不安装驱动，也能支持vga相关能力，但是性能不好。
- VGA 文本模式：没多大卵用了。
- 2D加速：没多大卵用了。
- spice + qxl 实现客户端2D加速：没多大卵用了。
- vhost-user virtio gpu：使用单独进程进行模拟virtio gpu。安全性更好。且opengl性能也好一些。
- qxl和qxl vga： 差别在于VGA compatibility。qxl （primary=‘no’）通常支持windows的多屏输出。
- cirrus vga：兼容90年代系统
- ramfb：通常用于boot阶段的显示输出，直到os加载vgpu驱动后。
使用建议
作者在文章末尾给出了使用建议。
For the desktop use case (assuming display performance matters and/or you need multihead support), in order of preference:
- virtio vga or virtio gpu, if your guest has drivers
- qxl vga, if your guest has drivers
- bochs display device, when using UEFI
- standard VGA
For the server use case (assuming the GUI is rarely used, or not at all), in order of preference:
- serial console, if you can work without a GUI
- bochs display device, when using UEFI
- standard VGA
On arm systems display devices with a pci memory bar do not work, which reduces the choices alot. We are left with:
- virtio gpu, if your guest has drivers
- ramfb