On Mon, Aug 13, 2012 at 02:12:41PM +0300, Gleb Natapov wrote:
> On Mon, Aug 13, 2012 at 02:03:51PM +0300, Avi Kivity wrote:
> > On 08/13/2012 02:01 PM, Gleb Natapov wrote:
> > >>
> > >> Actually this is overkill. Suppose we do an apicid->vcpu translation
> > >> cache? Then we retain O(1) behaviour, no need for a huge cache.
> > >>
> > > Not sure I follow.
> >
> > Unicast MSIs and IPIs can be speeded up by looking up the vcpu using the
> > apic id, using a static lookup table (only changed when the guest
> > updates apicid or a vcpu is inserted).
> >
> To check that MSI/IPI is unicast you need to check a lot of things: delivery
> mode, shorthand, dest mode, vector. In short everything but level. This
> is exactly what kvm_irq_delivery_to_apic() is doing. Caching apicid->vcpu
> is not enough, caching (delivery mode, shorthand, dest mode,
> vector)->vcpu is enough and this is exactly what the patch does for irq
> routing entries.
At least for MSI I think it is simple. Here's the relevant code from
my old patch:
+static bool kvm_msi_is_multicast(unsigned dest, int dest_mode)
+{
+ if (dest_mode == 0)
+ /* Physical mode. */
+ return dest == 0xff;
+ else
+ /* Logical mode. */
+ return dest & (dest - 1);
+}
> --
> Gleb.
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