On 03/10/2010 04:04 PM, Arnd Bergmann wrote:
On Tuesday 09 March 2010, Cam Macdonell wrote:
We could make the masking in RAM, not in registers, like virtio, which would
require no exits. It would then be part of the application specific
protocol and out of scope of of this spec.
This kind of implementation would be possible now since with UIO it's
up to the application whether to mask interrupts or not and what
interrupts mean. We could leave the interrupt mask register for those
who want that behaviour. Arnd's idea would remove the need for the
Doorbell and Mask, but we will always need at least one MMIO register
to send whatever interrupts we do send.
You'd also have to be very careful if the notification is in RAM to
avoid races between one guest triggering an interrupt and another
guest clearing its interrupt mask.
A totally different option that avoids this whole problem would
be to separate the signalling from the shared memory, making the
PCI shared memory device a trivial device with a single memory BAR,
and using something a higher-level concept like a virtio based
serial line for the actual signalling.
That would be much slower. The current scheme allows for an
ioeventfd/irqfd short circuit which allows one guest to interrupt
another without involving their qemus at all.
--
error compiling committee.c: too many arguments to function
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