Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool

[Andrea Arcangeli]

On Fri, Dec 12, 2008 at 09:23:10AM +0100, Jens Axboe wrote:
> aio is only async with O_DIRECT, with buffered IO it's sync.

That's very bad, because aio is as needed for O_DIRECT as for buffered
read seeking workloads that otherwise have zero chance to fill the
I/O pipe... (well unless one is threading in userland which is obviously
less efficient than what aio could achieve in kernel space, even
without taking cfq screwed bucketing into account).