On 04.06.2011, at 13:53, Ingo Molnar wrote: > > * Alexander Graf <agraf@xxxxxxx> wrote: > >> Why would you need panning/scrolling for a fast FB? It's really an >> optimization that helps a lot with VNC, but on local machines or >> SDL you shouldn't see a major difference. > > Qemu's fb console scrolling graphics is pretty slow to me even > locally so i assume that the dirty bitmap trick is not enough. > > VirtualBox graphics is very fast, but it probably has its own console > abstraction and scrolling/2D/3D acceleration. > > Also, since tools/kvm/ is really also about learning interesting > stuff, smooth scrolling was the historic first 'acceleration' usecase > that video graphics cards added - before they evolved more complex 2D > acceleration and then started doing 3D. > > Walking that path would allow us to do a gradual approach, while > still having relevant functionality and enhancements at every step. Sure, not saying scrolling is a bad thing to implement. I was merely trying to point out that the slowness you were seeing was not related to scrolling :). >> Unless you use the FB as MMIO. Qemu just maps the FB as RAM and >> checks for dirty bitmap updates periodically. That way you don't >> constantly exit due to MMIO and are good on speed. The slowness you >> describe sounds a lot as if you don't do that trick. > > Correct, and i assumed we already do the dirty-bitmap trick: > > KVM_MEM_LOG_DIRTY_PAGES > KVM_GET_DIRTY_LOG > > But you are right, we do not actually do that! > > Pekka, i think this should be the next step. We'll need scrolling > after that ... Yup. If you want to do graphics, dirty bitmaps are the way to go. Please be aware that the dirty bitmap is always little endian :). > In theory it would also be nice to tunnel the VGA text frame buffer > over to the KVM tool - as serial console is not supported by most > installers and default distro images. We could actually do a rather > good job of emulating it via Slang/Curses. Yep, works pretty well in Qemu. $ qemu -curses ... gives you the VGA text frame buffer through curses. Just in case you need some inspiration :) Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
