On Mon, Sep 26, 2005 at 09:48:25PM -0400, John Coiner wrote: > > Hi, > > Here's another patch to enable IDE DMA: > > http://people.brandeis.edu/~jcoiner/qemu_idedma/qemu_dma_patch.html > > This patch, like Juergen Lock's earlier patch from which it is derived, > replaces the virtual PIIX3 IDE controller with a PIIX4. > > It applies cleanly to 0.7.2. > > This patch extends the Windows 2000 install hack to work for DMA also -- > I installed and ran Windows 2000 with DMA enabled. > > It'd be cool if QEMU supported nonblocking disk access -- if it would > let the guest resume running currently, while waiting for the disk to > finish seeking. This patch is a first step toward concurrent IO, which > would probably have to use busmastering DMA transfers to be efficient, > if it's going to be efficient at all. > > Do people have ideas about how to implement concurrent IO? I have a > couple hazy ideas... > > Can anyone shed light on the potential performance to be realized? For > example, how long does a context switch take in the guest? If it takes > 10ms (one disk seek) then there's probably no benefit to concurrent disk > IO. If a context switch takes 1ms, then the guest has opportunity to > make forward progress while awaiting an IDE interrupt.
I would strongly suggest attempting to make use of the Linux Async I/O support.. this way the data from disk could be placed directly in address space of the guest OS. Personally, I'd love to see nonblocking disk IO. I've tried running Qemu using a disk image on an AFS filesystem, and having the guest be able to continue while the filesystem is fetching data from the network would make things much nicer. _______________________________________________ Qemu-devel mailing list Qemu-devel@nongnu.org http://lists.nongnu.org/mailman/listinfo/qemu-devel
