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Date: Mon, 18 Nov 2013 16:03:40 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20131118150340.GA4083@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] dataplane, thread and gpu stuff
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To: Dave Airlie <airlied@gmail.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

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.

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