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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] dataplane, thread and gpu stuff |
Date: | Mon, 18 Nov 2013 08:18:47 -0800 |
On Nov 18, 2013 7:05 AM, "Stefan Hajnoczi" <address@hidden> 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.
Regards,
Anthony Liguori
>
> Paolo can give you details on the latest thread-safe memory API stuff
> and whether it's already usable for virtio.
>
> Regarding irqfd, we could emulate it in TCG using an EventNotifier
> (eventfd). At that point I think it's no longer kvm-specific.
>
> Stefan
>
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