diff --git a/tools/xentrace/formats b/tools/xentrace/formats
index 8b31780..34ed9e4 100644
--- a/tools/xentrace/formats
+++ b/tools/xentrace/formats
@@ -125,6 +125,9 @@
 0x00082020  CPU%(cpu)d  %(tsc)d (+%(reltsc)8d)  INTR_WINDOW [ value = 0x%(1)08x ]
 0x00082021  CPU%(cpu)d  %(tsc)d (+%(reltsc)8d)  NPF         [ gpa = 0x%(2)08x%(1)08x mfn = 0x%(4)08x%(3)08x qual = 0x%(5)04x p2mt = 0x%(6)04x ]
 0x00082023  CPU%(cpu)d  %(tsc)d (+%(reltsc)8d)  TRAP        [ vector = 0x%(1)02x ]
+0x00082026  CPU%(cpu)d  %(tsc)d (+%(reltsc)8d)  PI_BLOCK_LIST  [ domid = 0x%(1)04x vcpu = 0x%(2)04x, pcpu = 0x%(3)04x, #entry = 0x%(4)04x ]
+0x00082027  CPU%(cpu)d  %(tsc)d (+%(reltsc)8d)  PI_WAKEUP_START [ list_len = 0x%(1)04x ]
+0x00082028  CPU%(cpu)d  %(tsc)d (+%(reltsc)8d)  PI_WAKEUP_END
 
 0x0010f001  CPU%(cpu)d  %(tsc)d (+%(reltsc)8d)  page_grant_map      [ domid = %(1)d ]
 0x0010f002  CPU%(cpu)d  %(tsc)d (+%(reltsc)8d)  page_grant_unmap    [ domid = %(1)d ]
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index c8ef18a..3a6640b 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -82,6 +82,7 @@ static int vmx_vmfunc_intercept(struct cpu_user_regs *regs);
 struct vmx_pi_blocking_vcpu {
     struct list_head     list;
     spinlock_t           lock;
+    atomic_t             counter;
 };
 
 /*
@@ -119,6 +120,9 @@ static void vmx_vcpu_block(struct vcpu *v)
      */
     ASSERT(old_lock == NULL);
 
+    atomic_inc(&per_cpu(vmx_pi_blocking, v->processor).counter);
+    HVMTRACE_4D(VT_D_PI_BLOCK, v->domain->domain_id, v->vcpu_id, v->processor,
+                atomic_read(&per_cpu(vmx_pi_blocking, v->processor).counter));
     list_add_tail(&v->arch.hvm_vmx.pi_blocking.list,
                   &per_cpu(vmx_pi_blocking, v->processor).list);
     spin_unlock_irqrestore(pi_blocking_list_lock, flags);
@@ -186,6 +190,8 @@ static void vmx_pi_unblock_vcpu(struct vcpu *v)
     {
         ASSERT(v->arch.hvm_vmx.pi_blocking.lock == pi_blocking_list_lock);
         list_del(&v->arch.hvm_vmx.pi_blocking.list);
+        atomic_dec(&container_of(pi_blocking_list_lock,
+                                 struct vmx_pi_blocking_vcpu, lock)->counter);
         v->arch.hvm_vmx.pi_blocking.lock = NULL;
     }
 
@@ -234,6 +240,7 @@ void vmx_pi_desc_fixup(unsigned int cpu)
         if ( pi_test_on(&vmx->pi_desc) )
         {
             list_del(&vmx->pi_blocking.list);
+            atomic_dec(&per_cpu(vmx_pi_blocking, cpu).counter);
             vmx->pi_blocking.lock = NULL;
             vcpu_unblock(container_of(vmx, struct vcpu, arch.hvm_vmx));
         }
@@ -2360,13 +2367,15 @@ static void pi_wakeup_interrupt(struct cpu_user_regs *regs)
     struct arch_vmx_struct *vmx, *tmp;
     spinlock_t *lock = &per_cpu(vmx_pi_blocking, smp_processor_id()).lock;
     struct list_head *blocked_vcpus =
-		&per_cpu(vmx_pi_blocking, smp_processor_id()).list;
+               &per_cpu(vmx_pi_blocking, smp_processor_id()).list;
 
     ack_APIC_irq();
     this_cpu(irq_count)++;
 
     spin_lock(lock);
 
+    TRACE_1D(TRC_HVM_PI_WAKEUP_START,
+        atomic_read(&per_cpu(vmx_pi_blocking, smp_processor_id()).counter));
     /*
      * XXX: The length of the list depends on how many vCPU is current
      * blocked on this specific pCPU. This may hurt the interrupt latency
@@ -2377,11 +2386,13 @@ static void pi_wakeup_interrupt(struct cpu_user_regs *regs)
         if ( pi_test_on(&vmx->pi_desc) )
         {
             list_del(&vmx->pi_blocking.list);
+            atomic_dec(&per_cpu(vmx_pi_blocking, smp_processor_id()).counter);
             ASSERT(vmx->pi_blocking.lock == lock);
             vmx->pi_blocking.lock = NULL;
             vcpu_unblock(container_of(vmx, struct vcpu, arch.hvm_vmx));
         }
     }
+    TRACE_0D(TRC_HVM_PI_WAKEUP_END);
 
     spin_unlock(lock);
 }
diff --git a/xen/include/asm-x86/hvm/trace.h b/xen/include/asm-x86/hvm/trace.h
index de802a6..afe8b75 100644
--- a/xen/include/asm-x86/hvm/trace.h
+++ b/xen/include/asm-x86/hvm/trace.h
@@ -54,6 +54,9 @@
 #define DO_TRC_HVM_TRAP             DEFAULT_HVM_MISC
 #define DO_TRC_HVM_TRAP_DEBUG       DEFAULT_HVM_MISC
 #define DO_TRC_HVM_VLAPIC           DEFAULT_HVM_MISC
+#define DO_TRC_HVM_VT_D_PI_BLOCK    DEFAULT_HVM_MISC
+#define DO_TRC_HVM_PI_WAKEUP_START  DEFAULT_HVM_MISC
+#define DO_TRC_HVM_PI_WAKEUP_END    DEFAULT_HVM_MISC
 
 
 #define TRC_PAR_LONG(par) ((par)&0xFFFFFFFF),((par)>>32)
diff --git a/xen/include/public/trace.h b/xen/include/public/trace.h
index 7f2e891..c5b95ee 100644
--- a/xen/include/public/trace.h
+++ b/xen/include/public/trace.h
@@ -234,6 +234,9 @@
 #define TRC_HVM_TRAP             (TRC_HVM_HANDLER + 0x23)
 #define TRC_HVM_TRAP_DEBUG       (TRC_HVM_HANDLER + 0x24)
 #define TRC_HVM_VLAPIC           (TRC_HVM_HANDLER + 0x25)
+#define TRC_HVM_VT_D_PI_BLOCK    (TRC_HVM_HANDLER + 0x26)
+#define TRC_HVM_PI_WAKEUP_START  (TRC_HVM_HANDLER + 0x27)
+#define TRC_HVM_PI_WAKEUP_END    (TRC_HVM_HANDLER + 0x28)
 
 #define TRC_HVM_IOPORT_WRITE    (TRC_HVM_HANDLER + 0x216)
 #define TRC_HVM_IOMEM_WRITE     (TRC_HVM_HANDLER + 0x217)
