Re: [kvm-devel] [Qemu-devel] Re: [PATCH 1/3] Refactor AIO interface to allow other AIO implementations

[Avi Kivity]

Anthony Liguori wrote:
> > If I submit sequential O_DIRECT reads with aio_read(), will they enter
> > the device read queue in the same order, and reach the disk in that
> > order (allowing for reordering when worthwhile by the elevator)?
> >   
>
> There's no guarantee that any sort of order will be preserved by AIO 
> requests.  The same is true with writes.  This is what fdsync is for, 
> to guarantee ordering.

I believe he'd like a hint to get good scheduling, not a guarantee.  
With a thread pool if the threads are scheduled out of order, so are 
your requests.  If the elevator doesn't plug the queue, the first few 
requests may not be optimally sorted.

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