Re: [Qemu-devel] dataplane, thread and gpu stuff

[Stefan Hajnoczi <stefanha@gmail.com>]

On Mon, Nov 18, 2013 at 08:18:47AM -0800, Anthony Liguori wrote:
> On Nov 18, 2013 7:05 AM, "Stefan Hajnoczi" <stefanha@gmail.com> wrote:
> >
> > On Mon, Nov 18, 2013 at 02:52:53PM +1000, Dave Airlie wrote:
> > > So after talking to a few people at kvm forum I think the GPU code
> > > should probably use the dataplane stuff from the outset,
> > >
> > > The main advantages I think this gives me is being able to dequeue
> > > objects from the vq from a thread and send irq vectors from there as
> > > well.
> > >
> > > Though since it appears the dataplane stuff is kvm specific (at least
> > > the irq handling), I was wondering how I should deal with fallbacks
> > > for non-kvm operation, and quite how much falling back I need to do.
> > >
> > > Can I still use the dataplane/vring code from the normal bottom half
> > > handlers or do I have to write separate code for both situations.
> >
> > As of today, there are still two vring implementations in
> > hw/virtio/virtio.c and hw/virtio/dataplane/vring.c.  This means it isn't
> > clean and easy to integrate into a new device yet.  Existing dataplane
> > devices basically take advantage of the fact that the non-dataplane
> > version sets up the device before I/O.
> 
> I think we also need some form of mdroth's GContext prior to introducing
> more dataplane devices.  Sticking every device in a seperate thread with no
> way to control who is where can actually hurt performance.  I think we
> really need to have a M-N device thread model too.

Yes, I agree.  We need the concept of multiple event loops (QContext).

Stefan