Il 05/12/2013 09:40, Matthias Brugger ha scritto: > CFQ the state of the art I/O scheduler
The deadline scheduler typically provides much better performance for server usage (including hosting VMs). It doesn't support some features such as I/O throttling via cgroups, but QEMU now has a very good throttling mechanism implemented by Benoit Canet. I suggest that you repeat your experiments using all six configurations: - deadline scheduler with aio=native - deadline scheduler with aio=threads - deadline scheduler with aio=threads + your patches - CFQ scheduler with aio=native - CFQ scheduler with aio=threads - CFQ scheduler with aio=threads + your patches > In former versions, there was some work done to merge requests in > Qemu, but I don't think they were very useful, because you don't know > how the layout of the image file looks like on the physical disk. > Anyway I think this code parts have been removed. This is still there for writes, in bdrv_aio_multiwrite. Only virtio-blk.c uses it, but it's there. > The only layer where you really know how the blocks of the virtual > disk image are distributed over the disk is the block layer of the > host. So you have to do the block request merging there. With the new > architecture this would come for free, as you can map every thread > from a guest to one workerthread of Qemu. This also assumes a relatively "dumb" guest. If the guest uses itself a thread pool, you would have exactly the same problem, wouldn't you? Paolo
