Re: qemu-kvm/rbd: first attempt to implement aio

[Yehuda Sadeh Weinraub <yehudasa@gmail.com>]

On Thu, Apr 15, 2010 at 1:24 PM, Christian Brunner <chb@muc.de> wrote:
> To increase the performance of the qemu rbd driver I started to implement
> aio functions. Attached is an intial aio implementation. However it is
> missing the callback of rados_aio_read or _write from time to time.
> This leads to a lockup of the disk driver until the guest OS is
> perfomring a bus reset.
>
> If someone has an explanation for the cause of the lost callbacks. I
> would be happy.
>

Yeah, it looks like the rados aio interface is racy. You should be
able to first set aio completion and only then to do the read/write
and not the other way around as it is now. I've just pushed a fix to
the unstable branch that changes the interface a bit. Now you first
need to do a rados_aio_create_completion() first and use it in the
rados_aio_read()/write() call. Note that I haven't tested it yet, so
let me know if there's any problem.


Thanks,
Yehuda