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

[Daniel P. Berrange]

On Thu, Apr 17, 2008 at 02:26:50PM -0500, Anthony Liguori wrote:
> Posix AIO, especially as used by QEMU, is not very efficient for disk IO.
> This patch introduces an AIO abstract to allow multiple AIO implements to be
> used.  We can't simply replace posix-aio by linux-aio because linux-aio only
> works on some filesystems and only with files opened with O_DIRECT.
> 
> This patch adds a command line option (-aio) to select the AIO implementation
> to be used.  It avoids code motion to allow for easy review.  The next patch
> separates out the posix-aio implementation.

This is not a very pleasant user experiance. They can not & should not be
expected to figure out which AIO impl works with their particular filesystem.
If the linux-aio impl doesn't work in some cases, then the code should detect
these and automatically fallback to posix-aio. The user should not have to
use a -aio flag to make it work.

Dan.
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