perfstat_cpu Subroutine

Purpose

Retrieves individual logical processor usage statistics.

Library

perfstat library (libperfstat.a)

Syntax

#include <libperfstat.h>

int perfstat_cpu (name, userbuff, sizeof_struct, desired_number)
perfstat_id_t * name;
perfstat_cpu_t * userbuff;
size_t sizeof_struct;
int desired_number;

Description

The perfstat_cpu subroutine retrieves one or more individual processor usage statistics. The same function can be used to retrieve the number of available sets of logical processor statistics.

To get one or more sets of processor usage metrics, set the name parameter to the name of the first processor for which statistics are wanted, and set the desired_number parameter. To start from the first processor, set the name parameter to "". The userbuff parameter must always point to a memory area significant enough to contain the wanted number of perfstat_cpu_t structures that will be copied by this function. Upon return, the name parameter will be set to either the name of the next processor, or to "" after all structures have been copied.

To retrieve the number of available sets of processor usage metrics, set the name and userbuff parameters to NULL, and the desired_number parameter to 0. The returned value is the number of available sets.

This number represents the number of logical processors for which statistics are available. In a dynamic logical partitioning (DLPAR) environment, this number is the highest logical index of an online processor since the last reboot. See the Perfstat API article in Performance Tools and APIs Technical Reference for more information on the perfstat_cpu subroutine and DLPAR.

The SPLPAR environments virtualize physical processors. To help accurately measure the resource use in a virtualized environment, the POWER5 family of processors implements a register PURR (Processor Utilization Resource Register) for each core. The PURR is a 64-bit counter with the same units as the timebase register and tracks the real physical processor resource that is used on a per-thread or per-partition level. The PURR registers are not compatible with previous global counters (user, system, idle, and wait fields) returned by the perfstat_cpu and the perfstat_cpu_total subroutines. All data consumers requiring processor utilization must be modified to support PURR-based computations as shown in the example for the perfstat_partition_total interface under Perfstat API programming.

This subroutine returns only global processor statistics inside a workload partition (WPAR).

Parameters

Table 1. Parameters
Item	Description
name	Contains either "", FIRST_CPU, or a name identifying the first logical processor for which statistics are wanted. Logical processor names are: `cpu0, cpu1,...` To provide binary compatibility with previous versions of the library, names like `proc0, proc1, ...` will still be accepted. These names are treated as if their corresponding `cpuN` name was used, but the names that are returned in the structures will always be names starting with `cpu`.
userbuff	Points to the memory area that is to be filled with one or more `perfstat_cpu_t` structures.
sizeof_struct	Specifies the size of the `perfstat_cpu_t` structure: `sizeof(perfstat_cpu_t)`.
desired_number	Specifies the number of `perfstat_cpu_t` structures to copy to `userbuff`.

Return Values

Unless the perfstat_cpu subroutine is used to retrieve the number of available structures, the number of structures that are filled is returned upon successful completion. If unsuccessful, a value of -1 is returned and the errno global variable is set.

Error Codes

The perfstat_cpu subroutine is unsuccessful if the following is true:

Table 2. Error Codes
Item	Description
`EINVAL`	One of the parameters is not valid.

Files

The libperfstat.h file defines standard macros, data types, and subroutines.