Re: [Qemu-devel] [PATCH 0/4] qcow2: Improve cluster refcount update

[Anthony Liguori]

Andreas Färber wrote:
> Am 07.11.2008 um 16:37 schrieb Anthony Liguori:
>
> > Laurent Vivier wrote:
> > > Le vendredi 07 novembre 2008 à 07:59 -0600, Anthony Liguori a écrit :
> > > In all cases #1 is totally useless as it is only cosmetic.
> > >
> > > #2 improves performance without aligned buffers and with "cache" set to
> > > default value.
> >
> > I'm currently rewriting the block-raw-posix.c O_DIRECT support.  I'll 
> > commit your patches once I finish that.
> >
> > I'm switching everything to use the aio functions,
>
> I'm not familiar with this area of code, so just as a reminder for 
> consideration, recently Blue Swirl added an option to disable AIO. 
> Some BSDs as well as Haiku may not have (full) POSIX AIO support. 
> Dumping non-AIO code for better performance on Linux would seem to 
> counterpoint the broadening platform support?

We can emulate AIO either via a bottom half and synchronous IO (not 
great) or using pthreads (better).  I have patches for both.  Mixing 
synchronous IO and asynchronous has all sorts of really ugly consequences.

Regards,

Anthony Liguori

> Andreas