diff -r fe930e1b2ce8 xen/arch/x86/io_apic.c
--- a/xen/arch/x86/io_apic.c	Fri Aug 06 18:35:02 2010 +0100
+++ b/xen/arch/x86/io_apic.c	Tue Aug 10 14:36:14 2010 +0100
@@ -446,6 +446,7 @@
     genapic->send_IPI_mask(&cleanup_mask, IRQ_MOVE_CLEANUP_VECTOR);
 
     cfg->move_in_progress = 0;
+    printk("%s: Done moving vec %d\n", __func__, cfg->vector);
 }
 
 void irq_complete_move(struct irq_desc **descp)
@@ -2266,7 +2267,10 @@
 
     vector = assign_irq_vector(irq);
     if (vector < 0)
+    {
+        printk("%s: assign_irq_vector returned %d\n", __func__, vector);
         return vector;
+    }
     entry.vector = vector;
 
     apic_printk(APIC_DEBUG, KERN_DEBUG "IOAPIC[%d]: Set PCI routing entry "
diff -r fe930e1b2ce8 xen/arch/x86/irq.c
--- a/xen/arch/x86/irq.c	Fri Aug 06 18:35:02 2010 +0100
+++ b/xen/arch/x86/irq.c	Tue Aug 10 14:36:14 2010 +0100
@@ -201,6 +201,7 @@
      }
 
     cfg->move_in_progress = 0;
+    printk("Done moving irq %d v %d\n", irq, cfg->vector);
 }
 
 void clear_irq_vector(int irq)
@@ -349,7 +350,13 @@
     cpumask_t tmp_mask;
 
     if ((cfg->move_in_progress) || cfg->move_cleanup_count)
+    {
+        if (cfg->move_in_progress)
+            printk("irq %d v%d: move_in_progress\n", irq, cfg->vector);
+        if (cfg->move_cleanup_count)
+            printk("irq %d v%d: move_cleanup_count\n", irq, cfg->vector);
         return -EBUSY;
+    }
 
     old_vector = irq_to_vector(irq);
     if (old_vector) {
@@ -391,9 +398,11 @@
             if (per_cpu(vector_irq, new_cpu)[vector] != -1)
                 goto next;
         /* Found one! */
+        printk("irq %d vec %d\n", irq, vector);
         current_vector = vector;
         current_offset = offset;
         if (old_vector) {
+            printk("irq %d moving vector %u\n", irq, old_vector);
             cfg->move_in_progress = 1;
             cpus_copy(cfg->old_domain, cfg->domain);
         }
@@ -422,7 +431,9 @@
 
     spin_lock_irqsave(&vector_lock, flags);
     ret = __assign_irq_vector(irq, cfg, TARGET_CPUS);
-    if (!ret) {
+    if ( ret < 0 )
+        printk("%s: __asign_irq_vector returned %d\n", __func__, ret);
+    else if (ret == 0) {
         ret = cfg->vector;
         cpus_copy(desc->affinity, cfg->domain);
     }
diff -r fe930e1b2ce8 xen/arch/x86/physdev.c
--- a/xen/arch/x86/physdev.c	Fri Aug 06 18:35:02 2010 +0100
+++ b/xen/arch/x86/physdev.c	Tue Aug 10 14:36:14 2010 +0100
@@ -478,6 +478,8 @@
             break;
         ret = mp_register_gsi(setup_gsi.gsi, setup_gsi.triggering,
                               setup_gsi.polarity);
+        if ( ret < 0 )
+            printk("PHYSDEVOP_setup_gsi: mp_register_gsi returned %d\n", (int)ret);
         break; 
     }
     default: