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A closely related utility, cputrack(1), can be used to monitor the behavior of individual applications with little or no interference from other activities
on the system.
The cpustat utility must be run by the super-user, as there is an intrinsic conflict between the use of the CPU performance counters system-wide by cpustat and the use of the CPU performance counters to monitor an individual
process (for example, by cputrack.)
Once any instance of this utility has started, no further per-process or per-LWP use of the counters is allowed until the last instance of the utility terminates.
The times printed by the command correspond to the wallclock time when the hardware counters were actually sampled, instead of when the program told the kernel to sample them. The time is derived from the same timebase as gethrtime(3C).
The processor cycle counts enabled by the -t option always apply to both user and system modes, regardless of the settings applied to the performance counter registers.
On some hardware platforms, the counters are implemented using 32-bit registers. While the kernel attempts to catch all overflows to synthesize 64-bit counters, because of hardware implementation restrictions, overflows may be lost unless the sampling interval is kept short enough. The events most
prone to wrap are those that count processor clock cycles. If such an event is of interest, sampling should occur frequently so that less than 4 billion clock cycles can occur between samples.
The output of cpustat is designed to be readily parseable by nawk(1) and perl(1), thereby allowing performance tools to be composed by embedding cpustat in scripts. Alternatively, tools may be constructed directly using the same APIs that cpustat is built upon using the facilities
of libcpc(3LIB). See cpc(3CPC).
The cpustat utility only monitors the CPUs that are accessible to it in the current processor set. Thus, several instances of the utility can be running on the CPUs in different processor sets. See psrset(1M) for more information about processor sets.
Because cpustat uses LWPs bound to CPUs, the utility may have to be terminated before the configuration of the relevant processor can be changed.
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