Implementing interrupt routing to least priority processor.
Instead of round robin the vcpu with the lowest processor
priority is selected for the interrupt. If multiple vcpus
share the same low priority interrupts are distributed between
those round robin.

Signed-off-by: juergen.gross@fujitsu-siemens.com

# HG changeset patch
# User juergen.gross@fujitsu-siemens.com
# Date 1227001650 -3600
# Node ID 370b052ca213bb03f234c102d72d774df6a5aa19
# Parent  7640fba355fac233773d183077d7d01c8fd591f3
implementing least priority interrupt routing

diff -r 7640fba355fa -r 370b052ca213 xen/arch/x86/hvm/vlapic.c
--- a/xen/arch/x86/hvm/vlapic.c	Tue Oct 28 09:47:35 2008 +0100
+++ b/xen/arch/x86/hvm/vlapic.c	Tue Nov 18 10:47:30 2008 +0100
@@ -380,25 +380,35 @@
 struct vlapic *apic_round_robin(
     struct domain *d, uint8_t vector, uint32_t bitmap)
 {
-    int next, old;
-    struct vlapic *target = NULL;
+    int old;
+    uint32_t ppr, ppr_min;
+    struct vlapic *target;
+    struct vlapic *target_min = NULL;
+    struct vcpu *v;
 
-    old = next = d->arch.hvm_domain.irq.round_robin_prev_vcpu;
+    old = d->arch.hvm_domain.irq.round_robin_prev_vcpu;
+    ppr_min = 256;
+    v = d->vcpu[old];
 
     do {
-        if ( ++next == MAX_VIRT_CPUS ) 
-            next = 0;
-        if ( (d->vcpu[next] == NULL) || !test_bit(next, &bitmap) )
+        v = v->next_in_list;
+	if ( v == NULL )
+	    v = d->vcpu[0];
+        if ( !test_bit(v->vcpu_id, &bitmap) )
             continue;
-        target = vcpu_vlapic(d->vcpu[next]);
-        if ( vlapic_enabled(target) )
-            break;
-        target = NULL;
-    } while ( next != old );
+        target = vcpu_vlapic(v);
+        if ( !vlapic_enabled(target) )
+            continue;
+        ppr = vlapic_get_ppr(target);
+	if ( ppr < ppr_min )
+	{
+	    target_min = target;
+	    ppr_min = ppr;
+	    d->arch.hvm_domain.irq.round_robin_prev_vcpu = v->vcpu_id;
+	}
+    } while ( v->vcpu_id != old );
 
-    d->arch.hvm_domain.irq.round_robin_prev_vcpu = next;
-
-    return target;
+    return target_min;
 }
 
 void vlapic_EOI_set(struct vlapic *vlapic)