On Mon, Aug 13, 2012 at 02:22:14PM +0300, Michael S. Tsirkin wrote: > 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); > +} > MSI does not have shorthand, so it is simpler but the code above does work for APIC_DFR_CLUSTER as far as I can tell and it does not check lowest prio, which is not multicast, but should bot be cached. -- Gleb. -- 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