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

[Anthony Liguori]

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.

> If it were just one operation in qcow2, threading would be a big 
> overkill.  But threading also fixes all of the other format drivers, 
> and makes working on qcow2 easier.

Yeah, I think the only question is whether to stick threading in the 
generic block layer or within qcow2.

Regards,

Anthony Liguori