Re: How is irq delivered in kvm?

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On 04/21/2011 05:23 PM, Nguyen Thai Ngoc Duy wrote:
On Thu, Apr 21, 2011 at 9:11 PM, Avi Kivity<avi@xxxxxxxxxx>  wrote:
>  On 04/21/2011 04:49 PM, Nguyen Thai Ngoc Duy wrote:
>>
>>  Hi,
>>
>>  I have a specialized e1000 device driver that expects to receive a
>>  single frame per interrupt, no more. It's by design and very hard to
>>  change (and it does not serve IP traffic). -net socket or tap can
>>  sometimes deliver more than one frame in a row and blow up the driver
>>  in turn. I'd like to experiment with tap/socket to only call
>>  qemu_send_packet..() once and leave pending frames in queue until next
>>  time, with hope that guest will have time to process the frame.
>
>  I don't understand how the driver can expect that.  The card is free to
>  deliver multiple packets per interrupt.  Are you counting on fast timing to
>  process the packet before the next packet arrives?

Yes. It uses ethernet as transport to "clone" memory from one machine
to another in a short, precalculated amount of time.

Well, anything time related will misbehave under virtualization.

>  If you restrict the number of buffers you provide to the card to exactly
>  one, you'll get one packet per interrupts (and dropped packets).
>
>>  The problem is I'm new to kvm and not sure how the main loop is run.
>>  Will there be guest execution time between two tap/socket polls, how
>>  long is it? Or is guest run in parallel with the event loop and
>>  qemu_set_irq() somehow signals guest immediately?
>
>  The latter, it's in parallel.
>
>  Are you using qemu-kvm or qemu?  qemu-kvm will deliver better interrupt
>  performance.

I'm using qemu-kvm. What function is used to deliver the interrupt
then, kvm_inject_irq?

No, kvm_set_irq_level().


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

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