The cpc_shared_open() function allows the caller to access the hardware counters in such a way that the performance of the currently bound CPU can be measured. The function returns a file descriptor if successful. Only one such open can be active at a time on any CPU.

The cpc_shared_bind_event(), cpc_shared_take_sample(), and cpc_shared_rele() functions are directly analogous to the corresponding cpc_bind_event(), cpc_take_sample(), and cpc_rele() functions described on the cpc_bind_event(3CPC)manual page, except that they operate on the counters of a particular processor.

If a thread wishes to access the counters using this interface, it must do so using a thread bound to an lwp, (see the THR_BOUND flag to thr_create(3THR)), that has in turn bound itself to a processor using processor_bind(2).

Unlike the cpc_bind_event(3CPC) family of functions, no counter context is attached to those lwps, so the performance counter samples from the processors reflects the system-wide usage, instead of per-lwp usage.

The first successful invocation of cpc_shared_open() will immediately invalidate all existing performance counter context on the system, and prevent all subsequent attempts to bind counter context to lwps from succeeding anywhere on the system until the last caller invokes cpc_shared_close().

This is because it is impossible to simultaneously use the counters to accurately measure per-lwp and system-wide events, so there is an exclusive interlock between these uses.

Access to the shared counters is mediated by file permissions on a cpc pseudo device. As shipped, only the superuser is allowed to access the shared device; this is because doing so prevents use of the counters on a per-lwp basis to any other users.

The CPC_BIND_LWP_INHERIT and CPC_BIND_EMT_OVF flags are invalid for the shared interface.

On success, the functions (apart from cpc_shared_close()) return 0. On failure, the functions return -1 and set errno, to indicate the reason.

ENXIO

The current machine either has no performance counters, or has been configured to disallow access to them system-wide.

EACCES

The caller does not have appropriate privilege to access the CPU performance counters system-wide.

EAGAIN

For cpc_shared_open(), this value implies that the counters on the bound cpu are busy because they are already being used to measure system-wide events by some other caller.

EAGAIN

Otherwise, this return value implies that the counters are not available because the thread has been unbound from the processor it was bound to at open time. Robust programs should be coded to expect this behavior, and should invoke cpc_shared_close(), before retrying the operation.

EINVAL

The counters cannot be accessed on the current CPU because the calling thread is not bound to that CPU using processor_bind(2).

EFAULT

The event argument specifies a bad address.

ENOTSUP

The caller has attempted an operation that is illegal or not supported on the current platform.

See attributes(5) for descriptions of the following attributes:

processor_bind(2), cpc(3CPC), cpc_bind_event(3CPC), thr_create(3THR), attributes(5)