On 03/09/2010 05:27 PM, Cam Macdonell wrote:
Registers are used
for synchronization between guests sharing the same memory object when
interrupts are supported (this requires using the shared memory server).
How does the driver detect whether interrupts are supported or not?
At the moment, the VM ID is set to -1 if interrupts aren't supported,
but that may not be the clearest way to do things. With UIO is there
a way to detect if the interrupt pin is on?
I suggest not designing the device to uio. Make it a good
guest-independent device, and if uio doesn't fit it, change it.
Why not support interrupts unconditionally? Is the device useful
without interrupts?
The Doorbell register is 16-bits, but is treated as two 8-bit values. The
upper 8-bits are used for the destination VM ID. The lower 8-bits are the
value which will be written to the destination VM and what the guest
status
register will be set to when the interrupt is trigger is the destination
guest.
What happens when two interrupts are sent back-to-back to the same guest?
Will the first status value be lost?
Right now, it would be. I believe that eventfd has a counting
semaphore option, that could prevent loss of status (but limits what
the status could be).
It only counts the number of interrupts (and kvm will coalesce them anyway).
My understanding of uio_pci interrupt handling
is fairly new, but we could have the uio driver store the interrupt
statuses to avoid losing them.
There's nowhere to store them if we use ioeventfd/irqfd. I think it's
both easier and more efficient to leave this to the application (to
store into shared memory).
--
error compiling committee.c: too many arguments to function
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