Re: [libvirt] [PATCH] qemu: Support ram bar size for qxl devices

Hi, It's all a bit more complicated ... Current upstream has *four* parameters here: qxl-vga.ram_size_mb=uint32 Size of PCI Bar 0. Default: 64. VGA framebuffer lives there, also qxl rendering commands and parameters (image data, clip regions, whatever) for the qxl rendering commands. qxl-vga.vram_size_mb=uint32 Size of PCI Bar 1. Default: 64. Storage for surfaces. Basically image data too, but you can do qxl raster ops on them. X11 uses this for offscreen pixmaps. qxl-vga.vram64_size_mb=uint32 There is an (optional) 64bit version of PCI Bar 1 (Bar 5 IIRC), which can be mapped above 4G. Both bars are backed by the same memory. qxl-vga.vgamem_mb=uint32 VGA framebuffer size. Default: 16. Specifies how much of the PCI bar 0 memory should be available for the VGA framebuffer. ram_size/vramsize is there too. Same as ram_size_mb/vram_size_mb, but they want bytes instead of megabytes. And to complete the picture: The other vga cards (std, cirrus, vmware) got vgamem_mb parameters too, which simply specify the size of the card's memory. For cirrus its pointless as the emulated hardware constrains the memory size and the only reason this is configurable in the first place is qemu <-> qemu-kvm live migration compatibility. For the other cards it makes sense to allow tuning the vgamem_mb parameter via domain xml. So, how expose this to the user? We already have 'vram'. Adding 'ram' makes sense. vram64 not so IMHO. I think it would be better to have a 64bit bool, then do this: if (64bit) qxl-vga.vram64_size_mb=${vram},vram_size_mb=1 else qxl-vga.vram_size_mb=${vram} Dunno what to do best with vgamem_mb for qxl. One more parameter? Or use ram_size/4? The other vga cards are a bit tricky too. If you add a cirrus or stdvga libvirt fills in vram='9216'. Where does *that* come from btw? It isn't the qemu default (used to be 8 MB, now 16 MB). It's also not the qemu-kvm default (was 16 MB all the time). And it isn't valid too (pci bar size must be a power of two). So reusing that for vgamem_mb is probably asking for trouble. So maybe the best and least confusing would be to add a vgamem parameter for all vga cards (including qxl, except cirrus)? cheers, Gerd