Re: [Qemu-devel] plan for device assignment upstream

[Michael S. Tsirkin]

On Mon, Jul 02, 2012 at 12:43:48PM +0300, Avi Kivity wrote:
> On 07/02/2012 12:30 PM, Jan Kiszka wrote:
> > On 2012-07-02 11:18, Michael S. Tsirkin wrote:
> >> I've been thinking hard about Jan's patches for device
> >> assignment. Basically while I thought it makes sense
> >> to make all devices: assignment and not - behave the
> >> same and use same APIs for injecting irqs, Anthony thinks there is huge
> >> value in making irq propagation hierarchical and device assignment
> >> should be special cased.
> > 
> > On the long term, we will need direct injection, ie. caching, to allow
> > making it lock-less. Stepping through all intermediate layers will cause
> > troubles, at least performance-wise, when having to take and drop a lock
> > at each stop.
> 
> So we precalculate everything beforehand.  Instead of each qemu_irq
> triggering a callback, calculating the next hop and firing the next
> qemu_irq, configure each qemu_irq array with a function that describes
> how to take the next hop.  Whenever the configuration changes,
> recalculate all routes.
> 
> For device assignment or vhost, we can have a qemu_irq_irqfd() which
> converts a qemu_irq to an eventfd.  If the route calculations determine
> that it can be serviced via a real irqfd, they also configure it as an
> irqfd.  Otherwise qemu configures a poll on this eventfd and calls the
> callback when needed.

This is more or less what I had in mind and what Anthony objects to.

> -- 
> error compiling committee.c: too many arguments to function
>