KVM: selftests: Time guest demand paging

In order to quantify demand paging performance, time guest execution
during demand paging.

Signed-off-by: Ben Gardon <bgardon@google.com>
[Move timespec-diff to test_util.h]
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/lib/test_util.c

@@ -49,3 +49,23 @@ size_t parse_size(const char *size)
 
 	return base << shift;
 }
+
+int64_t timespec_to_ns(struct timespec ts)
+{
+	return (int64_t)ts.tv_nsec + 1000000000LL * (int64_t)ts.tv_sec;
+}
+
+struct timespec timespec_diff(struct timespec start, struct timespec end)
+{
+	struct timespec temp;
+
+	if ((end.tv_nsec - start.tv_nsec) < 0) {
+		temp.tv_sec = end.tv_sec - start.tv_sec - 1;
+		temp.tv_nsec = 1000000000LL + end.tv_nsec - start.tv_nsec;
+	} else {
+		temp.tv_sec = end.tv_sec - start.tv_sec;
+		temp.tv_nsec = end.tv_nsec - start.tv_nsec;
+	}
+
+	return temp;
+}