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

[Anthony Liguori]

Avi Kivity wrote:
> Anthony Liguori wrote:
> > 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, introducing a 
> > memory pool so that we can efficiently allocate memory for new 
> > requests without having unbounded memory allocation, and switching 
> > all the synchronous functions to use the aio functions.
>
> What about locking?  If clusters are already allocated and we don't 
> need COW things are simple (and a global lock should suffice, provided 
> it's released before the io is actually submitted), but are you 
> planning to parallelize the metadata paths as well?

I'm still doing a global lock model and requests submitted while a 
request is pending is simply queued.  There are certainly more effective 
strategies but this will work for now.

My larger goal is to totally eliminate synchronous reads/writes APIs in 
QEMU.  They cause unending pain with the main loop.

Regards,

Anthony Liguori