Re: [Qemu-devel] [PATCH 0/8] virtio-console: Move to qdev, multiple devices, generic ports

[Anthony Liguori]

On 01/14/2010 09:34 AM, Amit Shah wrote:
> On (Thu) Jan 14 2010 [08:34:42], Anthony Liguori wrote:
>    
> > On 01/14/2010 07:17 AM, Amit Shah wrote:
> >      
> > > Hello people,
> > >
> > > This iteration of the series removes the START and END flags (and
> > > hence the header associated with each buffer). That's the major change
> > > since the last submission.
> > >
> > >        
> > I think the biggest issue remaining is the buffering.
> >
> > I think this is a pretty fundamental issue to work out since it
> > determines the very nature of the transport (stream vs. datagram).
> >      
> The buffering is done so that the guest copy of the buffer is acked so
> that the guest can go about doing other things. (Currently the guest
> spins till a buffer is acked by the host and waiting for individual
> ports to flush their data to whichever receiver will consume some time.)
>    

The guest already gets an ack when data is consumed.  The host adds the 
consumed buffer to the used ring.

> This also puts buffer management in one place: not all ports will
> consume all the data given to them. There's a need to maintain the
> buffer contents till the ports consume all the data. This buffer
> management can either be done by the individual ports, or it could be
> done by the bus code. I prefer doing it in the bus code since the code
> will be the same and be in one place instead of each port doing it
> separately all around the place.
>    

The rings themselves are buffers.  Since each port has a ring, each port 
has independent buffering right now.

Regards,

Anthony Liguori