On 12/02/2009 02:59 PM, Chris Lalancette wrote:
On 12/01/2009 08:04 PM, Jan Kiszka wrote:
Chris Lalancette wrote:
KVM_REQ_PENDING_TIMER is set and cleared in a couple of places,
but it never seems to be actually checked. Remove it.
I would suggest to study the introducing commit
06e05645661211b9eaadaf6344c335d2e80f0ba2. My strong feeling is that this
removal is wrong.
Ah, thanks. Now I see what you mean. In newer KVM, if you are in
__vcpu_run() and are in the while (r> 0) loop, after you've
done kvm_inject_pending_timer_irqs(), but before you do the next
__vcpu_run() (and hence disabled local IRQs), you could receive an
hrtimer callback. In that case I guess you would hit the
if (vcpu->requests || need_resched() || signal_pending()) test, don't
inject the interrupt, and possibly spend a long time in the guest
before an unrelated event causes the exit and hence causes the timer
injection.
Well, that certainly is a bit subtle :). I think I might submit a
patch to at least put a comment in vcpu_enter_guest() about this.
It is, and I don't like it much either.
Unfortunately, this does sort of put a damper on what's going on later
in the series. If the i8254 doesn't belong to the BSP (which it really
shouldn't), then I don't know which vcpu to raise the bit on. Maybe I
can do it in the kvm_irq_delivery_to_apic() function, or
kvm_apic_set_irq(). I'll take a look at that.
We shouldn't have that bit at all.
An alternative is to make the pic/ioapic work in irq context
(spin_lock_irq() and friends) and queue the interrupt directly from the
hrtimer instead of the vcpu. My worry is that we have quite a bit of
work to do in irq context if the interrupt is broadcast and if we have
many vcpus; maybe we can use a work_struct in that case.
--
error compiling committee.c: too many arguments to function
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