Re: [Qemu-devel] [PATCH -V3 09/32] virtio-9p: Implement P9_TWRITE/ Thread model in QEMU

[Anthony Liguori]

On 03/30/2010 09:23 AM, Avi Kivity wrote:
> On 03/30/2010 05:07 PM, Anthony Liguori wrote:
> > On 03/30/2010 09:03 AM, Avi Kivity wrote:
> > > > So it looks like we really only have one operation 
> > > > (qcow2_alloc_cluster_link_l2) that blocks.  Do we really think that 
> > > > it's sufficiently difficult to make this function asynchronous that 
> > > > it justifies threading the block layer?
> > >
> > > There are also tons of bdrv_pread()s and bdrv_pwrite()s.  Isn't 
> > > growing some of the tables synchronous? how about creating a snapshot?
> >
> > Eh, that ruins my whole argument.
>
>
> But we can keep on arguing regardless, yes?

Of course :-)

> Both.  My plan is:
>
> (1) some generic infrastructure
> (2) kit that turns a synchronous block format driver into an 
> asynchronous one using (1), limited to one outstanding request
> (3) adaptations to qcow2 using (1) to make it fully asynchronous, 
> capable of multiple outstanding requests (except when it issues a sync 
> request)
>
> I've mostly done (1) and am contemplating (2).

Sounds reasonable.

Regards,

Anthony Liguori