Re: [kvm-devel] [PATCH 10/13] KVM: Wire up hypercall handlers toa central arch-independent location

From: Avi Kivity
Date: Thu Feb 22 2007 - 09:22:09 EST

Arjan van de Ven wrote:
Can't it be done by a helper function using a timer and a signal (or whatever mechanism we use to wake up vcpus)?

one could do that but it's not optimal; if the process DOES get waken up
earlier, it should take the interrupt then immediately, so that it
doesn't have to wake up again when the timer fires.

(in fact it would be nice if the guest could somehow poll at the irq
mask at waking from idle, so that it wouldn't need a vmexit/entry for
every such interrupt, but just do the right thing for all pending work)

In addition, yes it'll be a helper function, but since all drivers will
want the functionality its probably best off in the generic code

That's what Xen does (I'm not sure about the timer, but they do avoid unnecessary interrupts). As you can have memory shared between the guest and host, it's quite simple:

0. host puts data in ring
1. host sets interrupt timer
2. guest wakes up for unrelated reasons
3. guest sees data in ring, consumes it, and bumps the consumer pointer
4. timer fires, host sees consumer == producer, no need to issue interrupt

They have that code abstracted out and reusable by multiple drivers.

error compiling committee.c: too many arguments to function

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