cpc(3CPC)					    CPU Performance Counters Library Functions						 cpc(3CPC)

NAME

       cpc - hardware performance counters

DESCRIPTION

       Modern  microprocessors	contain  hardware performance counters that allow the measurement of many different hardware events related to CPU
       behavior, including instruction and data cache misses as well as various internal states of the processor. The counters can  be	configured
       to  count  user events, system events, or both. Data from the performance counters can be used to analyze and tune the behavior of software
       on a particular type of processor.

       Most processors are able to generate an interrupt on counter overflow, allowing the counters to be used for various forms of profiling.

       This manual page describes a set of APIs that allow Solaris applications to use these counters. Applications can measure their  own  behav-
       ior, the behavior of other applications, or the behavior of the whole system.

   Shared Counters or Private Counters
       There  are  two principal models for using these performance counters. Some users of these statistics want to observe system-wide behavior.
       Other users want to view the performance counters as part of the register set exported by each LWP. On a machine performing more  than  one
       activity,  these  two models are in conflict because the counters represent a critical hardware resource that cannot simultaneously be both
       shared and private.

   Configuration Interfaces
       The following configuration interfaces are provided:

       cpc_open(3CPC)	       Check the version the application was compiled with against the version of the library.

       cpc_cciname(3CPC)       Return a printable string to describe the performance counters of the processor.

       cpc_npic(3CPC)	       Return the number of performance counters on the processor.

       cpc_cpuref(3CPC)        Return a reference to documentation that should be consulted to understand how to use and interpret data  from  the
			       performance counters.

   Performance Counter Access
       Performance counters can be present in hardware but not acccessible because either some of the necessary system software components are not
       available or not installed, or the counters might be in use by other processes.	The cpc_open(3CPC) function determines	the  accessibility
       of the counters and must be invoked before any attempt to program the counters.

   Finding Events
       Each   different   type	 of   processor  has  its  own	set  of  events  available  for  measurement.  The  cpc_walk_events_all(3CPC)  and
       cpc_walk_events_pic(3CPC) functions allow an application to determine the names of events supported by the underlying processor.

   Using Attributes
       Some processors have advanced performance counter capabilities that are configured with attributes. The cpc_walk_attrs(3CPC)  function  can
       be used to determine the names of attributes supported by the underlying processor. The documentation referenced by cpc_cpuref(3CPC) should
       be consulted to understand the meaning of a processor's performance counter attributes.

   Performance Counter Context
       Each processor on the system possesses its own set of performance counter registers. For a single process, it is often desirable  to  main-
       tain  the  illusion that the counters are an intrinsic part of that process (whichever processors it runs on), since this allows the events
       to be directly attributed to the process without having to make passive all other activity on the system.

       To achieve this behavior, the library associates performance counter context with each LWP in the process. The context consists of a  small
       amount  of kernel memory to hold the counter values when the LWP is not running, and some simple kernel functions to save and restore those
       counter values from and to the hardware registers when the LWP performs a normal context switch. A process can only observe and	manipulate
       its own copy of the performance counter control and data registers.

   Performance Counters In Other Processes
       Though  applications  can  be  modified	to  instrument themselves as demonstrated above, it is frequently useful to be able to examine the
       behavior of an existing application without changing the source code. A separate library, libpctx, provides a simple set of interfaces that
       use  the facilities of proc(4) to control a target process, and together with functions in libcpc, allow truss-like tools to be constructed
       to measure the performance counters in other applications. An example of one such application is cputrack(1).

       The functions in libpctx are independent of those in libcpc. These functions manage a process using an event-loop paradigm -- that is,  the
       execution of certain system calls by the controlled process cause the library to stop the controlled process and execute callback functions
       in the context of the controlling process. These handlers can perform various operations on the target process using APIs  in  libpctx  and
       libcpc that consume pctx_t handles.

SEE ALSO

       cputrack(1),  cpustat(1M),  cpc_bind_curlwp(3CPC),  cpc_buf_create(3CPC),  cpc_enable(3CPC),  cpc_npic(3CPC),  cpc_open(3CPC), cpc_set_cre-
       ate(3CPC), cpc_seterrhndlr(3CPC), libcpc(3LIB), pctx_capture(3CPC), pctx_set_events(3CPC), proc(4).

SunOS 5.10							    30 Jan 2004 							 cpc(3CPC)