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.
Regards, happy hacking,
John
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