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SubjectRe: O_NONBLOCK is NOOP on block devices
On 3/10/10 2:21 PM, Jeff Moyer wrote:
> M vd S <> writes:
>> I also briefly tried aio_* and the libaio interface. The former is not
>> really asynchronous - all requests are put in one separate thread
>> where they will be executed in order, i.e. blocking, so you don't get
>> any advantage from NCQ or data that was cached by the disk or the
>> kernel. The latter apparently ends in an io_submit() which will block
>> until all queued reads are finished, but I might have missed something
>> there.
> What you missed is that the native aio system calls require O_DIRECT.

Thanks, that made it work. It seems without O_DIRECT it's just like
aio_* but without the separate thread. But I now get the "benefits" of
O_DIRECT for free...


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