Re: [Qemu-devel] Re: [RFT][PATCH 07/15] qemu_irq: Add IRQ handlers with delivery feedback

[Jan Kiszka]

Gleb Natapov wrote:
> On Sat, Jun 05, 2010 at 02:04:01AM +0200, Jan Kiszka wrote:
>>> I'd like to also support EOI handling. When the guest clears the
>>> interrupt condtion, the EOI callback would be called. This could occur
>>> much later than the IRQ delivery time. I'm not sure if we need the
>>> result code in that case.
>>>
>>> If any intermediate device (IOAPIC?) needs to be informed about either
>>> delivery or EOI also, it could create a proxy message with its
>>> callbacks in place. But we need then a separate opaque field (in
>>> addition to payload) to store the original message.
>>>
>>> struct IRQMsg {
>>>  DeviceState *src;
>>>  void (*delivery_cb)(IRQMsg *msg, int result);
>>>  void (*eoi_cb)(IRQMsg *msg, int result);
>>>  void *src_opaque;
>>>  void *payload;
>>> };
>> Extending the lifetime of IRQMsg objects beyond the delivery call stack
>> means qemu_malloc/free for every delivery. I think it takes a _very_
>> appealing reason to justify this. But so far I do not see any use case
>> for eio_cb at all.
>>
> I dislike use of eoi for reinfecting missing interrupts since
> it eliminates use of internal PIC/APIC queue of not yet delivered
> interrupts. PIC and APIC has internal queue that can handle two elements:
> one is delivered, but not yet acked interrupt in isr and another is
> pending interrupt in irr. Using eoi callback (or ack notifier as it's
> called inside kernel) interrupt will be considered coalesced even if irr
> is cleared, but no ack was received for previously delivered interrupt.
> But ack notifiers actually has another use: device assignment. There is
> a plan to move device assignment from kernel to userspace and for that
> ack notifiers will have to be extended to userspace too. If so we can
> use them to do irq decoalescing as well. I doubt they should be part
> of IRQMsg though. Why not do what kernel does: have globally registered
> notifier based on irqchip/pin.

I read this twice but I still don't get your plan. Do you like or
dislike using EIO for de-coalescing? And how should these notifiers work?

Jan

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