Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O

[Paul Brook]

On Monday 03 December 2007, Samuel Thibault wrote:
> Anthony Liguori, le Mon 03 Dec 2007 09:54:47 -0600, a écrit :
> > Have you done any performance testing?  Buffered IO should absolutely
> > beat direct IO simply because buffered IO allows writes to complete
> > before they actually hit disk.
>
> Since qemu can use the aio interface, that shouldn't matter.

Only if the emulated hardware and guest OS support multiple concurrent 
commands.  IDE supports async operation, but not concurrent commmands. In 
practice this means you only get full performance if you're using the SCSI 
emulation.

Paul