linux-kernel - Re: O_NONBLOCK is NOOP on block devices

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Message-ID: <4B97D258.7060702@gmail.com>
Date:	Wed, 10 Mar 2010 18:09:44 +0100
From:	M vd S <mvds.00@...il.com>
To:	Jeff Moyer <jmoyer@...hat.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: O_NONBLOCK is NOOP on block devices

On 3/10/10 2:21 PM, Jeff Moyer wrote:
> M vd S <mvds.00@...il.com> 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...

Cheers,
M.

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