it can be improved. Here's my version:

log_error = 1;
log_debug = 0;

#define	LOG_PRINT(_log_level, _type, _fmt, _args...) do {
	if ((_log_level))
		warnx("%lld " _type _fmt,
		    tick_diff_secs(rel_time, rdtsc()), ##_args);
	} while(0)

#define	ERR_PRINT(fmt, args...)
	LOG_PRINT(log_error,"ERROR: ",  fmt, ##args)

#define	DBG_PRINT(fmt, args...)
	LOG_PRINT(log_debug, "DEBUG: ", fmt, ##args)

/* */
ERR_PRINT("%d", some_int_var);
DBG_PRINT("%d", some_int_var); // goes silent bcz log_debug = 0