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 pro-
cessor. 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 behavior, 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 perfor-
mance 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:
cpcopen(3CPC) Check the version the application was
compiled with against the version of
the library.
cpccciname(3CPC) Return a printable string to describe
the performance counters of the proces-
sor.
cpcnpic(3CPC) Return the number of performance
counters on the processor.
SunOS 5.11 Last change: 8 Oct 2008 1
CPU Performance Counters Library Functions cpc(3CPC)
cpccpuref(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
cpcopen(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 cpcwalkeventsall(3CPC) and
cpcwalkeventspic(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 genericevents(3CPC). Each gen-
eric event maps to an underlying hardware event specific to
the underlying processor and any optional attributes. The
cpcwalkgenericeventsall(3CPC) and
cpcwalkgenericeventspic(3CPC) functions allow an appli-
cation to determine the generic events supported on the
underlying platform.
Using Attributes
Some processors have advanced performance counter capabili-
ties that are configured with attributes. The
cpcwalkattrs(3CPC) function can be used to determine the
names of attributes supported by the underlying processor.
The documentation referenced by cpccpuref(3CPC) should be
consulted to understand the meaning of a processor's perfor-
mance counter attributes.
Performance Counter Context
Each processor on the system possesses its own set of per-
formance counter registers. For a single process, it is
often desirable to maintain 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
SunOS 5.11 Last change: 8 Oct 2008 2
CPU Performance Counters Library Functions cpc(3CPC)
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 mani-
pulate 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, pro-
vides a simple set of interfaces that use the facilities of
proc(4) to control a target process, and together with func-
tions 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 para-
digm - 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 pctxt handles.
SEE ALSO
cputrack(1), cpustat(1M), cpcbindcurlwp(3CPC),
cpcbufcreate(3CPC), cpcenable(3CPC), cpcnpic(3CPC),
cpcopen(3CPC), cpcsetcreate(3CPC), cpcseterrhndlr(3CPC),
genericevents(3CPC), libcpc(3LIB), pctxcapture(3CPC),
pctxsetevents(3CPC), proc(4)
SunOS 5.11 Last change: 8 Oct 2008 3
|
