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8.3.7 Invalid timing measurements

Although the coNCePTuaL configure script is usually good at selecting a mechanism for measuring elapsed time, there are a few systems that confuse the script. For example, different Intel processors use different mechanisms for mapping cycle counts to time (cf.; the correct mapping cannot always be determined at configuration time and may require administrator privileges to calculate. Consequently, if configure determines that the coNCePTuaL timer should read the cycle counter directly, incorrect times may be reported.

The best way to test the timer quality is to run the validatetimer program (see Validating the coNCePTuaL timer). If the difference between wall-clock time and coNCePTuaL-reported time is great, the --with-gettimeofday configuration option (see configure) is usually a safe bet for improving accuracy, albeit at a slight cost in measurement overhead.

Scott Pakin,