On 10/27/07, Blue Swirl <blauwirbel@gmail.com> wrote:
> I changed Slirp output to use vectored IO to avoid the slowdown from
> memcpy (see the patch for the work in progress, gives a small
> performance improvement). But then I got the idea that using AIO would
> be nice at the outgoing end of the network IO processing. In fact,
> vectored AIO model could even be used for the generic DMA! The benefit
> is that no buffering or copying should be needed.

I made a sketch of the API, please have a look at the patch.

> Each stage would translate the IO list and callback as needed and only
> the final stage would perform the IO or memcpy. This would be used in
> each stage of the chain memory<->IOMMU<->device<->SLIRP<->host network
> device. Of course some kind of host support for vectored AIO for these
> devices is required. On target side, devices that can do
> scatter/gather DMA would benefit most.

Inside Qemu the vectors would use target physical addresses (struct
qemu_iovec), but at some point the addresses would change to host
pointers suitable for real AIO.