High Resolution Timers

TAU employs low-overhead high-resolution timers for performance measurements on several systems. On Cray XD1, TAU uses the high resolution time stamp counter register. On Cray X1, it uses the _rtc() call to measure clock ticks. On Cray XT3, it uses the dclock() call. By default, the ubiquitous gettimeofday() call is used. Profiling does not need a globally synchronized real-time clock like tracing. Thus, it is better to use the free-running timers on individual cpus for profiling and to use the default synchronized clocks for tracing program executions. The user can choose these high resolution timers during configuration by specifying the -CRAYTIMERS configuration option.