[Qemu-devel] [patch] Concurrent IO Support

[John Coiner <jcoiner@stanfordalumni.org>]

Folks,

Here's a patch which allows guest CPU cycles to run concurrent with IO 
syscalls:

http://people.brandeis.edu/~jcoiner/qemu_idedma/qemu_dma_patch.html

It's actually two patches -- a patch which enables DMA support (the same 
one posted here a few days ago) and a second patch which applies on top 
of the first. The second patch is the big one, because there was a 
little bit of refactoring and a few chunks of new code needed to get 
concurrent IO going.

If you try this, please let me know what your experience is. This patch 
makes the IDE code a little more gnarly, so it's only worth applying if 
people notice the speed-up.

Under both CPU load and IO load, the patch improves the performance of 
each, at least on my system. I haven't seen it make anything slower yet.

Troy and Henrik: thanks for suggesting AIO. That is probably the way to 
go. This patch uses pthreads, because I was more comfortable with them. 
The Linux Posix AIO stuff looked a little young. In the future, though, 
it should be pretty easy to convert this implementation to AIO.

Regards,

--John