KVM: trace kvm_halt_poll_ns grow/shrink

Tracepoint for dynamic halt_pool_ns, fired on every potential change.
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/trace/events/kvm.h

@@ -356,6 +356,36 @@ TRACE_EVENT(
 		  __entry->address)
 );
 
+TRACE_EVENT(kvm_halt_poll_ns,
+	TP_PROTO(bool grow, unsigned int vcpu_id, int new, int old),
+	TP_ARGS(grow, vcpu_id, new, old),
+
+	TP_STRUCT__entry(
+		__field(bool, grow)
+		__field(unsigned int, vcpu_id)
+		__field(int, new)
+		__field(int, old)
+	),
+
+	TP_fast_assign(
+		__entry->grow           = grow;
+		__entry->vcpu_id        = vcpu_id;
+		__entry->new            = new;
+		__entry->old            = old;
+	),
+
+	TP_printk("vcpu %u: halt_poll_ns %d (%s %d)",
+			__entry->vcpu_id,
+			__entry->new,
+			__entry->grow ? "grow" : "shrink",
+			__entry->old)
+);
+
+#define trace_kvm_halt_poll_ns_grow(vcpu_id, new, old) \
+	trace_kvm_halt_poll_ns(true, vcpu_id, new, old)
+#define trace_kvm_halt_poll_ns_shrink(vcpu_id, new, old) \
+	trace_kvm_halt_poll_ns(false, vcpu_id, new, old)
+
 #endif
 
 #endif /* _TRACE_KVM_MAIN_H */

virt/kvm/kvm_main.c

@@ -1918,8 +1918,9 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_mark_page_dirty);
 
 static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 {
-	int val = vcpu->halt_poll_ns;
+	int old, val;
 
+	old = val = vcpu->halt_poll_ns;
 	/* 10us base */
 	if (val == 0 && halt_poll_ns_grow)
 		val = 10000;
@@ -1927,18 +1928,21 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
 		val *= halt_poll_ns_grow;
 
 	vcpu->halt_poll_ns = val;
+	trace_kvm_halt_poll_ns_grow(vcpu->vcpu_id, val, old);
 }
 
 static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu)
 {
-	int val = vcpu->halt_poll_ns;
+	int old, val;
 
+	old = val = vcpu->halt_poll_ns;
 	if (halt_poll_ns_shrink == 0)
 		val = 0;
 	else
 		val /= halt_poll_ns_shrink;
 
 	vcpu->halt_poll_ns = val;
+	trace_kvm_halt_poll_ns_shrink(vcpu->vcpu_id, val, old);
 }
 
 static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)