On 05/16/2010 12:01 PM, Alexander Graf wrote:
That's what the world looked like in 2006.
We could change it, but there's not much point, since having the local apic in the kernel is pretty much a requirement for reasonable performance.
Well, I'm not convinced yet that's the case for PPC as well. The timer is in-cpu anyways and I don't see why IPIs should be slow with a userspace pic - if we keep the overhead low.
If it's at all possible keep the mpic out. I am _not_ advocating
pushing ppc's mpic into the kernel.
So let me think this through. With remote interrupt injection we have.
* thread 1 does vcpu_run
* thread 2 triggers KVM_INTERRUPT on fd
* thread 2 signals thread 1 so we're sure the interrupt gets injected
* thread 1 exits into qemu
This doesn't seem necessary. The kernel can own the interrupt line, so
it remembers it from the last KVM_INTERRUPT.
* thread 1 goes back into the vcpu, triggering an interrupt
Without we have:
* thread 1 does vcpu_run
* thread 2 wants to trigger an an interrupt, sets the qemu internal bit
* thread 2 signals thread 1 so we're sure the interrupt gets processed
* thread 1 exits into qemu
* thread 1 triggers KVM_INTERRUPT on fd
* thread 1 goes into the vcpu
So we don't really buy anything from doing the remote injection. Hrm.
Not if you make interrupt injection a lightweight exit.
What's somewhat striking me here though is - why do we need KVM_INTERRUPT when there's all those kvm_run fields? Can't we just do interrupt injection by setting run->trigger_interrupt? There's only a single "interrupt line" on the CPU anyways. That way we'd save the ioctl and get rid of the locking problem altogether.
That's what x86 does. However, it's synchronous.
--
error compiling committee.c: too many arguments to function
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
