Re: [PATCH v4] KVM: Introduce direct MSI message injection for in-kernel irqchips

[Avi Kivity <avi@redhat.com>]

On 04/04/2012 12:38 PM, Jan Kiszka wrote:
> On 2012-04-04 11:36, Avi Kivity wrote:
> > On 04/04/2012 12:22 PM, Jan Kiszka wrote:
> >>>
> >>>>> Until we do have this fast path we can just fill this value with zeros,
> >>>>> so kernel patch (almost) does not need to change for this -
> >>>>> just the header.
> >>>>
> >>>> Partially implemented interfaces invite breakage.
> >>>
> >>> Hmm true. OK scrap this idea then, it's not clear
> >>> whether we are going to optimize this anyway.
> >>>
> >>
> >> Also, the problem is that keeping that ID in userspace requires an
> >> infrastructure like the MSIRoutingCache that I proposed originally. Not
> >> much won /wrt invasiveness there. 
> > 
> > Internal qemu refactorings are not a driver for kvm interface changes.
>
> No, but qemu demonstrates the applicability and handiness of the kernel
> interfaces.

True.

> > 
> >> So we should really do the routing
> >> optimization in the kernel - one day.
> > 
> > No, we need to make a choice:
> > 
> > explicit handles: array lookup, more expensive setup
> > no handles: hash loopup, more expensive, but no setup, and no artificial
> > limits
>
> ...and I think we should head for option 2.

I'm not so sure anymore.  Sorry about the U turn, but remind me why?  In
the long term it will be slower.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.