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

[Jan Kiszka <jan.kiszka@siemens.com>]

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.

> 
>> 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.

Jan

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