Re: [PATCH] KVM: Remove arch specific components from the general code

[Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>]

On Thu, 2007-07-26 at 19:50 -0400, Gregory Haskins wrote: 
> On Fri, 2007-07-27 at 09:27 +1000, Rusty Russell wrote:
> 
> > So the in-kernel apic code has to traverse every element in the array?
> > That is clearly better because?
> 
> I can't speak for Eddie's implementation, but the one that I had worked
> on did in fact take advantage of the array.   Not for traversing it as
> you suggested, but rather for efficient mapping of vcpu ID to APIC.  The
> modeled "APIC BUS" already knew its targets.  It would then use
> "kvm->vcpus[target]" to find the right APIC.

That makes sense.  Looks like Eddie's ioapic code uses a similar trick
in ioapic_deliver's dest_Fixed case.

I'll revert to an array, but I'll drop the nvcpus var: scanning for
NULLs is so fast it won't be measurable.

> >   We get to place an artificial maximum
> > and keep a ceiling variable like the existing code does?
> 
> This always bothered me too.  But I guess realistically some reasonable
> ceiling could probably be found (something in the 8-64 range sounds
> right to me) if the dynamic list idea is shot down.  If we do go this
> static route, it should probably be in the Kconfig.

I agree: Qemu supports up to 255 processors, but that's kind of silly if
it's static.  I'll leave the current limit (4) and let someone else code
up a dynamic one.

Thanks!
Rusty.


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