Re: [PATCH 1/2] kvm tools: Fix IRQ assignments

[Cyrill Gorcunov <gorcunov@gmail.com>]

On 05/06/2011 11:36 AM, Sasha Levin wrote:
> On Fri, 2011-05-06 at 10:29 +0300, Pekka Enberg wrote:
>> On Fri, May 6, 2011 at 10:26 AM, Sasha Levin <levinsasha928@gmail.com> wrote:
>>> virtio-blk needs a block of 4 IRQs (currently - staticly defined).
>>> Giving the initial IRQ of 15 causes breakage when adding more
>>> than one device.
>>>
>>> Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
>>
>> Can we make the allocation dynamic instead? AFAICT, it could be a simple as
>>
>>   int kvm__request_irq(struct kvm *kvm)
>>   {
>>           return kvm->next_irq++;
>>   }
>>
>> that's done at device init time and then we'd just add "int irq" to
>> the individual struct devices.
>>
>>                         Pekka
> 
> afaik, we need to have same IRQ pins for devices which may have
> different IRQ lines (All virtio-blk share same IRQ pin but different
> line, I assume it'll be same with different virtio devices).
> 
> So mptable has to manage association between device type and the
> corresponding IRQ pin/line assignment, So dynamic assignment will be
> more of a call with device type and return IRQ pin + line - which makes
> it more complex than just allocating next free IRQ line.
> 

  Nod, making it dynamic force us to implement some kind of collector for
pci devices, so that it would know pin/vector pair for every device. So
in device init time we need to call kinda mptable_request_irq_pin()
where we could "hint" allocator which pin and irq we need, and say "exclusive"
flag which would tell allocator to fail if irq/pin already borrowed.

  The "hints" for every device might left hardcoded in some enum, for other
irqs we might need pure dynamic vector allocator.

-- 
Thanks,
  Cyrill