Limitations on Hardware Counter Overflow Profiling

Hardware counter overflow profiling has several limitations:

• You can only collect hardware counter overflow data on processors that have hardware counters and that support overflow profiling. On other systems, hardware counter overflow profiling is disabled. UltraSPARC® processors prior to the UltraSPARC III processor family do not support hardware counter overflow profiling.

• You cannot collect hardware counter overflow data on a system while cpustat(1) is running, because cpustat takes control of the counters and does not let a user process use the counters. If cpustat is started during data collection, the hardware counter overflow profiling is terminated and an error is recorded in the experiment.

• You cannot use the hardware counters in your own code with the libcpc(3) API if you are doing hardware counter overflow profiling. The Collector interposes on the libcpc library functions and returns with a return value of -1 if the call did not come from the Collector. Your program should be coded so as to work correctly if it fails to get access to the hardware counters. If not coded to handle this, the program will fail under hardware counter profiling, or if the root invokes system-wide tools that also use the counters.

• If you try to collect hardware counter data on a running program that is using the hardware counter library by attaching dbx to the process, the experiment may be corrupted.

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  Note –

  To view a list of all available counters, run the collect command with no arguments.

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