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

Avi Kivity
2008-04-22T15:05:32Z

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.

--
error compiling committee.c: too many arguments to function