CPC(3CPC)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 behav‐
ior, 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 applica‐
tions 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 regis‐
ter set exported by each LWP. On a machine performing more than one
activity, these two models are in conflict because the counters repre‐
sent 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 perfor‐
mance 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. A collection
of generic, platform independent event names are defined by
generic_events(3CPC). Each generic event maps to an underlying hard‐
ware event specific to the underlying processor and any optional
attributes. The cpc_walk_generic_events_all(3CPC) and
cpc_walk_generic_events_pic(3CPC) functions allow an application to
determine the generic events supported on the underlying platform.
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 demon‐
strated above, it is frequently useful to be able to examine the behav‐
ior of an existing application without changing the source code. A sep‐
arate 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 ALSOcputrack(1), cpustat(1M), cpc_bind_curlwp(3CPC), cpc_buf_create(3CPC),
cpc_enable(3CPC), cpc_npic(3CPC), cpc_open(3CPC), cpc_set_create(3CPC),
cpc_seterrhndlr(3CPC), generic_events(3CPC), libcpc(3LIB), pctx_cap‐
ture(3CPC), pctx_set_events(3CPC), proc(4)
Oct 8, 2008 CPC(3CPC)