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MPI Programming Guide

Glossary

A

address
A value, possibly a character or group of characters that identifies a register, a device, a particular part of storage, or some other data source or destination.

AIX
Abbreviation for Advanced Interactive Executive, IBM's licensed version of the UNIX operating system. AIX is particularly suited to support technical computing applications, including high-function graphics and floating-point computations.

AIXwindows(R) Environment/6000
A graphical user interface (GUI) for the IBM e(logo)server pSeries and IBM RS/6000 systems. It has the following components:

API
See application programming interface.

application
The use to which a data processing system is put; for example, topayroll application, an airline reservation application.

application programming interface
A set of programming functions and routines that provide access between the Application layer of the OSI seven-layer model and applications that want to use the network. It is a software interface.

argument
A parameter passed between a calling program and a called program or subprogram.

attribute
A named property of an entity.

B

bandwidth
The difference, expressed in hertz, between the highest and the lowest frequencies of a range of frequencies. For example, analog transmission by recognizable voice telephone requires a bandwidth of about 3000 hertz (3 kHz). The bandwidth of an optical link designates the information-carrying capacity of the link and is related to the maximum bit rate that a fiber link can support.

blocking operation
An operation that does not complete until the operation either succeeds or fails. For example, a blocking receive will not return until a message is received or until the channel is closed and no further messages can be received.

breakpoint
A place in a program, specified by a command or a condition, where the system halts execution and gives control to the workstation user or to a specified program.

broadcast operation
A communication operation in which one processor sends (or broadcasts) a message to all other processors.

buffer
A portion of storage used to hold input or output data temporarily.

C

C
A general-purpose programming language. It was formalized by Uniforum in 1983 and the ANSI standards committee for the C language in 1984.

C++
A general-purpose programming language that is based on the C language. C++ includes extensions that support an object-oriented programming paradigm. Extensions include:

call arc
The representation of a call between two functions within the Xprofiler function call tree. It appears as a solid line between the two functions. The arrowhead indicates the direction of the call; the function it points to is the one that receives the call. The function making the call is known as the caller, while the function receiving the call is known as the callee.

chaotic relaxation
An iterative relaxation method which uses a combination of the Gauss-Seidel and Jacobi-Seidel methods. The array of discrete values is divided into sub-regions that can be operated on in parallel. The sub-region boundaries are calculated using Jacobi-Seidel, whereas the sub-region interiors are calculated using Gauss-Seidel. See also Gauss-Seidel.

client
A function that requests services from a server and makes them available to the user.

cluster
A group of processors interconnected through a high-speed network that can be used for high-performance computing. A cluster typically provides excellent price/performance.

collective communication
A communication operation that involves more than two processes or tasks. Broadcasts, reductions, and the MPI_Allreduce subroutine are all examples of collective communication operations. All tasks in a communicator must participate.

command alias
When using the PE command line debugger pdbx, you can create abbreviations for existing commands using the pdbx alias command. These abbreviations are known as command aliases.

Communication Subsystem (CSS)
A component of the IBM Parallel System Support Programs for AIX that provides software support for the SP Switch. CSS provides two protocols: Internet Protocol (IP) for LAN-based communication and user space (US) as a message-passing interface that is optimized for performance over the switch. See also Internet Protocol and user space.

communicator
An MPI object that describes the communication context and an associated group of processes.

compile
To translate a source program into an executable program.

condition
One of a set of specified values that a data item can assume.

control workstation
A workstation attached to the IBM RS/6000 SP that serves as a single point of control allowing the administrator or operator to monitor and manage the system using IBM Parallel System Support Programs for AIX.

core dump
A process by which the current state of a program is preserved in a file. Core dumps are usually associated with programs that have encountered an unexpected, system-detected fault, such as a Segmentation Fault or a severe user error. The current program state is needed for the programmer to diagnose and correct the problem.

core file
A file that preserves the state of a program, usually just before a program is terminated for an unexpected error. See also core dump.

current context
When using the pdbx debugger, control of the parallel program and the display of its data can be limited to a subset of the tasks belonging to that program. This subset of tasks is called the current context. You can set the current context to be a single task, multiple tasks, or all the tasks in the program.

D

data decomposition
A method of breaking up (or decomposing) a program into smaller parts to exploit parallelism. One divides the program by dividing the data (usually arrays) into smaller parts and operating on each part independently.

data parallelism
Refers to situations where parallel tasks perform the same computation on different sets of data.

dbx
A symbolic command line debugger that is often provided with UNIX systems. The PE command line debugger pdbx is based on the dbx debugger.

debugger
A debugger provides an environment in which you can manually control the execution of a program. It also provides the ability to display the program' data and operation.

distributed shell (dsh)
A PSSP command that lets you issue commands to a group of hosts in parallel. See IBM Parallel System Support Programs for AIX: Command and Technical Reference for details.

domain name
The hierarchical identification of a host system (in a network), consisting of human-readable labels, separated by decimals.

E

environment variable
1) A variable that describes the operating environment of the process. Common environment variables describe the home directory, command search path, and the current time zone. 2) A variable that is included in the current software environment and is therefore available to any called program that requests it.

Ethernet
A baseband local area network (LAN) that allows multiple stations to access the transmission medium at will without prior coordination, avoids contention by using carrier sense and deference, and resolves contention by using collision detection and delayed retransmission. Ethernet uses carrier sense multiple access with collision detection (CSMA/CD).

event
An occurrence of significance to a task -- the completion of an asynchronous operation such as an input/output operation, for example.

executable
A program that has been link-edited and therefore can be run in a processor.

execution
To perform the actions specified by a program or a portion of a program.

expression
In programming languages, a language construct for computing a value from one or more operands.

F

fairness
A policy in which tasks, threads, or processes must be allowed eventual access to a resource for which they are competing. For example, if multiple threads are simultaneously seeking a lock, no set of circumstances can cause any thread to wait indefinitely for access to the lock.

FDDI
See Fiber Distributed Data Interface.

Fiber Distributed Data Interface (FDDI)
An American National Standards Institute (ANSI) standard for a local area network (LAN) using optical fiber cables. An FDDI LAN can be up to 100 kilometers (62 miles) and can include up to 500 system units. There can be up to 2 kilometers (1.24 miles) between system units and concentrators.

file system
In the AIX operating system, the collection of files and file management structures on a physical or logical mass storage device, such as a diskette or minidisk.

fileset
1) An individually-installable option or update. Options provide specific functions. Updates correct an error in, or enhance, a previously installed program. 2) One or more separately-installable, logically-grouped units in an installation package. See also licensed program and package.

foreign host
See remote host.

FORTRAN
One of the oldest of the modern programming languages, and the most popular language for scientific and engineering computations. Its name is a contraction of FORmula TRANslation. The two most common FORTRAN versions are FORTRAN 77, originally standardized in 1978, and FORTRAN 90. FORTRAN 77 is a proper subset of FORTRAN 90.

function call tree
A graphical representation of all the functions and calls within an application, which appears in the Xprofiler main window. The functions are represented by green, solid-filled rectangles called function boxes. The size and shape of each function box indicates its CPU usage. Calls between functions are represented by blue arrows, called call arcs, drawn between the function boxes. See also call arcs.

function cycle
A chain of calls in which the first caller is also the last to be called. A function that calls itself recursively is not considered a function cycle.

functional decomposition
A method of dividing the work in a program to exploit parallelism. One divides the program into independent pieces of functionality, which are distributed to independent processors. This method is in contrast to data decomposition, which distributes the same work over different data to independent processors.

functional parallelism
Refers to situations where parallel tasks specialize in particular work.

G

Gauss-Seidel
An iterative relaxation method for solving Laplace's equation. It calculates the general solution by finding particular solutions to a set of discrete points distributed throughout the area in question. The values of the individual points are obtained by averaging the values of nearby points. Gauss-Seidel differs from Jacobi-Seidel in that, for the i+1st iteration, Jacobi-Seidel uses only values calculated in the ith iteration. Gauss-Seidel uses a mixture of values calculated in the ith and i+1st iterations.

global max
The maximum value across all processors for a given variable. It is global in the sense that it is global to the available processors.

global variable
A variable defined in one portion of a computer program and used in at least one other portion of the computer program.

gprof
A UNIX command that produces an execution profile of C, COBOL, FORTRAN, or Pascal programs. The execution profile is in a textual and tabular format. It is useful for identifying which routines use the most CPU time. See the man page on gprof.

graphical user interface (GUI)
A type of computer interface consisting of a visual metaphor of a real-world scene, often of a desktop. Within that scene are icons, which represent actual objects, that the user can access and manipulate with a pointing device.

GUI
See Graphical user interface.

H

HIPPI
High performance parallel interface.

hook
A pdbx command that lets you re-establish control over all tasks in the current context that were previously unhooked with this command.

home node
The node from which an application developer compiles and runs his program. The home node can be any workstation on the LAN.

host
A computer connected to a network that provides an access method to that network. A host provides end-user services.

host list file
A file that contains a list of host names, and possibly other information, that was defined by the application which reads it.

host name
The name used to uniquely identify any computer on a network.

hot spot
A memory location or synchronization resource for which multiple processors compete excessively. This competition can cause a disproportionately large performance degradation when one processor that seeks the resource blocks, preventing many other processors from having it, thereby forcing them to become idle.

I

IBM Parallel Environment for AIX (PE)
A licensed program that provides an execution and development environment for parallel C, C++, and FORTRAN programs. PE also includes tools for debugging, profiling, and tuning parallel programs.

installation image
A file or collection of files that are required in order to install a software product on an IBM e(logo)server pSeries or IBM RS/6000 workstation, or on SP system nodes. These files are in a form that allows them to be installed or removed with the AIX installp command. See also fileset, licensed program, and package.

IBM Parallel System Support Programs for AIX (PSSP)
A comprehensive suite of applications that is used to manage an RS/6000 SP system as a full-function parallel-processing system. PSSP provides a single point of control for administrative tasks and helps increase productivity by letting administrators view, monitor, and control how the system operates.

Internet
The collection of worldwide networks and gateways that function as a single, cooperative virtual network.

Internet Protocol (IP)
1) The TCP/IP protocol that provides packet delivery between the hardware and user processes. 2) The SP Switch library, provided with the IBM Parallel System Support Programs for AIX, that follows the IP protocol of TCP/IP.

IP
Internet Protocol.

J

Jacobi-Seidel
See Gauss-Seidel.

Jumpshot
A public domain tool, developed at Argonne National Laboratory, for visualizing program performance. Jumpshot reads files in a scalable log file format, called SLOG. The PE Benchmarker toolset provides the slogmerge utility to enable you to convert UTE files into the SLOG format.

K

Kerberos
A publicly available security and authentication product that works with the IBM Parallel System Support Programs for AIX software to authenticate the execution of remote commands.

kernel
The core portion of the UNIX operating system that controls the resources of the CPU and allocates them to the users. The kernel is memory-resident, is said to run in kernel mode (in other words, at higher execution priority level than user mode), and is protected from user tampering by the hardware.

L

LAPI
See low-level communication API.

Laplace's equation
A homogeneous partial differential equation used to describe heat transfer, electric fields, and many other applications.

The dimension-free version of Laplace's equation is:

latency
The time interval between the instant at which an instruction control unit initiates a call for data transmission, and the instant at which the actual transfer of data (or receipt of data at the remote end) begins. Latency is related to the hardware characteristics of the system and to the different layers of software that are involved in initiating the task of packing and transmitting the data.

licensed program
A collection of software packages sold as a product that customers pay for to license. A licensed program can consist of packages and filesets a customer would install. These packages and filesets bear a copyright and are offered under the terms and conditions of a licensing agreement. See also fileset and package.

lightweight corefiles
An alternative to standard AIX corefiles. Corefiles produced in the Standardized Lightweight Corefile Format provide simple process stack traces (listings of function calls that led to the error) and consume fewer system resources than traditional corefiles.

LoadLeveler
A job management system that works with POE to let users run jobs and match processing needs with system resources, in order to make better use of the system.

local variable
A variable that is defined and used only in one specified portion of a computer program.

loop unrolling
A program transformation that makes multiple copies of the body of a loop, also placing the copies within the body of the loop. The loop trip count and index are adjusted appropriately so the new loop computes the same values as the original. This transformation makes it possible for a compiler to take additional advantage of instruction pipelining, data cache effects, and software pipelining.

See also optimization.

low-level communication API (LAPI)
A low-level (low overhead) message-passing protocol that uses a one-sided, active-message-style interface to transfer messages between processes. LAPI is an IBM proprietary interface that exploits the SP Switch adapters.

M

menu
A list of options displayed to the user by a data processing system, from which the user can select an action to be initiated.

message catalog
A file created using the AIX Message Facility from a message source file that contains application error and other messages, which can later be translated into other languages without having to recompile the application source code.

message passing
Refers to the process by which parallel tasks explicitly exchange program data.

message passing client interface (MPCI)
The primary interface to the pointtopoint message-passing protocols that support the SP Switch and the SP Switch2.

message passing interface (MPI)
An industry-standard message-passing protocol that typically uses a two-sided send-receive model to transfer messages between processes.

MIMD
See multiple instruction stream, multiple data stream.

MPCI
See message passing client interface.

MPMD
See Multiple program, multiple data.

multiple program, multiple data (MPMD)
A parallel programming model in which different, but related, programs are run on different sets of data.

MPI
See message passing interface.

multiple instruction stream, multiple data stream (MIMD)
A parallel programming model in which different processors perform different instructions on different sets of data.

N

netCDF file
See network Common Data Form (netCDF) file.

network
An interconnected group of nodes, lines, and terminals. A network provides the ability to transmit data to and receive data from other systems and users.

network Common Data Form (netCDF) file
A file using the netCDF format developed at the Unidata Program Center -- a program funded by the National Science Foundation (NSF). In the PE Benchmarker toolset, the PVT reads netCDF files containing hardware and operating system profiles output by the PCT.

Network Information Services (NIS)
A set of UNIX network services (for example, a distributed service for retrieving information about the users, groups, network addresses, and gateways in a network) that resolve naming and addressing differences among computers in a network.

NIS
See Network Information Services.

node
(1) In a network, the point where one or more functional units interconnect transmission lines. A computer location defined in a network. (2) In terms of the IBM RS/6000 SP, a single location or workstation in a network. An SP node is a physical entity (a processor).

node ID
A string of unique characters that identifies the node on a network.

nonblocking operation
An operation, such as sending or receiving a message, that returns immediately whether or not the operation was completed. For example, a nonblocking receive will not wait until a message is sent, but a blocking receive will wait. A nonblocking receive will return a status value that indicates whether or not a message was received.

O

object code
The result of translating a computer program to a relocatable, low-level form. Object code contains machine instructions, but symbol names (such as array, scalar, and procedure names), are not yet given a location in memory. Contrast with source code.

optimization
A widely-used (though not strictly accurate) term for program performance improvement, especially for performance improvement done by a compiler or other program translation software. An optimizing compiler is one that performs extensive code transformations in order to obtain an executable that runs faster but gives the same answer as the original. Such code transformations, however, can make code debugging and performance analysis very difficult because complex code transformations obscure the correspondence between compiled and original source code.

option flag
Arguments or any other additional information that a user specifies with a program name. Also referred to as parameters or command line options.

P

package
A number of filesets that have been collected into a single installable image of licensed programs. Multiple filesets can be bundled together for installing groups of software together. See also fileset and licensed program.

Parallel Environment
See IBM Parallel Environment for AIX.

parallelism
The degree to which parts of a program may be concurrently executed.

parallelize
To convert a serial program for parallel execution.

Parallel System Support Programs
See IBM Parallel System Support Programs for AIX.

parallel operating environment (POE)
An execution environment that smooths the differences between serial and parallel execution. POE lets you submit and manage parallel jobs.

parameter
(1) In FORTRAN, a symbol that is given a constant value for a specified application. (2) An item in a menu for which the operator specifies a value or for which the system provides a value when the menu is interpreted. (3) A name in a procedure that is used to refer to an argument that is passed to the procedure. (4) A particular piece of information that a system or application program needs to process a request.

partition
(1) A fixed-size division of storage. (2) In terms of the IBM RS/6000 SP, a logical definition of nodes to be viewed as one system or domain. System partitioning is a method of organizing the SP into groups of nodes for testing or running different levels of software of product environments.

Partition Manager
The component of the parallel operating environment (POE) that allocates nodes, sets up the execution environment for remote tasks, and manages distribution or collection of standard input (STDIN), standard output (STDOUT), and standard error (STDERR).

PCT
See Performance Collection Tool.

pdbx
PE's parallel, symbolic command-line debugging facility. pdbx is based on the dbx debugger and has a similar interface.

PE
See IBM Parallel Environment for AIX.

PE Benchmarker
A suite of applications and utilities that you can use to analyze the performance of programs run within IBM Parallel Environment for AIX. The PE Benchmarker toolset consists of the Performance Collection Tool (PCT), the Profile Visualization Tool (PVT), and a set of Unified Trace Environment (UTE) utilities.

Performance Collection Tool (PCT)
Part of the PE Benchmarker toolset, this tool enables you to collect either MPI and user event data or hardware and operating system profiles for one or more application processes. Because it is built on dynamic instrumentation technology, the PCT enables you to insert instrumentation probes into a target application while the target application is running.

performance monitor
A utility that displays how effectively a system is being used by programs.

PID
See process identifier.

point-to-point communication
A communication operation which involves exactly two processes or tasks. One process initiates the communication through a send operation. The partner process issues a receive operation to accept the data being sent.

POE
See parallel operating environment.

pool
Groups of nodes on an SP that are known to LoadLeveler, and are identified by a pool name or number.

procedure
(1) In a programming language, a block, with or without formal parameters, whose execution is invoked by means of a procedure call. (2) A set of related control statements that cause one or more programs to be performed.

process
A program or command that is actually running the computer. It consists of a loaded version of the executable file, its data, its stack, and its kernel data structures that represent the process's state within a multitasking environment. The executable file contains the machine instructions (and any calls to shared objects) that will be executed by the hardware. A process can contain multiple threads of execution.

The process is created via a fork() system call and ends using an exit() system call. Between fork and exit, the process is known to the system by a unique process identifier (PID).

Each process has its own virtual memory space and cannot access another process's memory directly. Communication methods across processes include pipes, sockets, shared memory, and message passing.

process identifier (PID)
An integer used by the Unix kernel to uniquely identify a process. PIDs are returned by the fork system call and can be passed to wait() or kill() to perform actions on the given process.

prof
A utility that produces an execution profile of an application or program. prof is useful for identifying which routines use the most CPU time.

Profile Visualization Tool (PVT)
Part of the PE Benchmarker toolset, this tool reads the hardware or operating system profiles output by the PCT in netCDF format. The PVT enables you to summarize the collected information in reports.

profiling
The act of determining how much CPU time is used by each function or subroutine in a program. The histogram or table produced is called the execution profile.

Program Marker Array
An X-Windows run time monitor tool provided with parallel operating environment, used to provide immediate visual feedback on a program's execution.

PSSP
See IBM Parallel System Support Programs for AIX.

pthread
A thread that conforms to the POSIX Threads Programming Model.

PVT
See Profile Visualization Tool.

R

reduced instruction set computer (RISC)
A computer that uses a small, simplified set of frequently-used instructions for rapid execution.

reduction operation
An operation, usually mathematical, that reduces a collection of data by one or more dimensions. For example, the arithmetic SUM operation is a reduction operation which reduces an array to a scalar value. Other reduction operations include MAXVAL and MINVAL.

remote host
Any host on a network except the one at which a particular operator is working.

remote shell (rsh)
A command supplied with both AIX and the IBM Parallel System Support Programs for AIX that lets you issue commands on a remote host.

Report
In Xprofiler, a tabular listing of performance data that is derived from the gmon.out files of an application. Xprofiler generates five types of reports. Each type of report presents different statistical information for an application.

RISC
See reduced instruction set computer.

RS/6000 SP
A scalable parallel system arranged in various physical configurations that provides a high-powered computing environment.

S

segmentation fault
A system-detected error, usually caused by referencing an non-valid memory address.

server
A functional unit that provides shared services to workstations over a network -- a file server, a print server, or a mail server, for example.

shell script
A sequence of commands that are to be executed by a shell interpreter such as the Bourne shell (sh), the C shell (csh), or the Korn shell (ksh). Script commands are stored in a file in the same form as if they were typed at a terminal.

signal handling
A type of communication that is used by message passing libraries. Signal handling involves using AIX signals as an asynchronous way to move data in and out of message buffers.

single program, multiple data (SPMD)
A parallel programming model in which different processors execute the same program on different sets of data.

SLOG file
A file using the scalable log file format. The Jumpshot tool from Argonne National Laboratory reads files of this format. The slogmerge utility of the PE Benchmarker toolset converts UTE files into the SLOG file format.

source code
The input to a compiler or assembler, written in a source language. Contrast with object code.

source line
A line of source code.

SP
See RS/6000 SP.

SPMD
See single program, multiple data.

SP Switch
The high-performance message-passing network of the IBM RS/6000 SP system that connects all processor nodes.

standard error (STDERR)
(1) An output file intended to be used for error messages for C programs. (2) In many workstation-based operating systems, the output stream to which error messages or diagnostic messages are sent.

standard input (STDIN)
In the AIX operating system, the primary source of data entered into a command. Standard input comes from the keyboard unless redirection or piping is used, in which case standard input can be from a file or the output from another command.

standard output (STDOUT)
In the AIX operating system, the primary destination of data produced by a command. Standard output goes to the display unless redirection or piping is used, in which case standard output can go to a file or to another command.

STDERR
See standard error.

STDIN
See standard input.

STDOUT
See standard output.

stencil
A pattern of memory references used for averaging. A 4-point stencil in two dimensions for a given array cell, x(i,j), uses the four adjacent cells, x(i-1,j), x(i+1,j), x(i,j-1), and x(i,j+1).

subroutine
(1) A sequence of instructions whose execution is invoked by a call. (2) A sequenced set of instructions or statements that may be used in one or more computer programs and at one or more points in a computer program. (3) A group of instructions that can be part of another routine or can be called by another program or routine.

synchronization
The action of forcing certain points in the execution sequences of two or more asynchronous procedures to coincide in time.

system administrator
(1) The person at a computer installation who designs, controls, and manages the use of the computer system. (2) The person who is responsible for setting up, modifying, and maintaining the Parallel Environment.

System Data Repository
A component of the IBM Parallel System Support Programs for AIX software that provides configuration management for the SP system. It manages the storage and retrieval of system data across the control workstation, file servers, and nodes.

T

target application
See DPCL target application.

task
A unit of computation analogous to an AIX process.

thread
A single, separately dispatchable, unit of execution. There may be one or more threads in a process, and each thread is executed by the operating system concurrently.

tracing
In PE, the collection of information about the execution of the program. This information is accumulated into a trace file that can later be examined.

tracepoint
Tracepoints are places in the program that, when reached during execution, cause the debugger to print information about the state of the program.

trace record
In PE, a collection of information about a specific event that occurred during the execution of your program. For example, a trace record is created for each send and receive operation that occurs in your program (this is optional and may not be appropriate). These records are then accumulated into a trace file that can later be examined.

U

Unified Trace Environment (UTE)
An environment that is used to generate, analyze, and visualize trace events for applications running on IBM RS/6000 SP systems.

unrolling loops
See loop unrolling.

US
See user space.

user
(1) A person who requires the services of a computing system. (2) Any person or any thing that may issue or receive commands and message to or from the information processing system.

user space (US)
A version of the message passing library that is optimized for direct access to the SP Switch, that maximizes the performance capabilities of the SP hardware.

UTE
See Unified Trace Environment.

UTE interval files
A Unified Trace Environment file that is distinct from an AIX trace file by the inclusion of interval information. While an AIX trace file has a time stamp indicating the point in time when an event occurred, UTE interval files also determine how long an event lasts before encountering the next event. Because they include this duration information, UTE interval files are easier to visualize than traditional AIX event trace files.

utility program
A computer program in general support of computer processes; for example, a diagnostic program, a trace program, a sort program.

utility routine
A routine in general support of the processes of a computer; for example, an input routine.

V

variable
(1) In programming languages, a named object that may take different values, one at a time. The values of a variable are usually restricted to one data type. (2) A quantity that can assume any of a given set of values. (3) A name used to represent a data item whose value can be changed while the program is running. (4) A name used to represent data whose value can be changed, while the program is running, by referring to the name of the variable.

view
(1) To display and look at data on screen.

(2) A special display of data, created as needed. A view temporarily ties two or more files together so that the combined files can be displayed, printed, or queried. The user specifies the fields to be included. The original files are not permanently linked or altered; however, if the system allows editing, the data in the original files will be changed.

X

X Window System
The UNIX industry's graphics windowing standard that provides simultaneous views of several executing programs or processes on high resolution graphics displays.

Xprofiler
An AIX tool that is used to analyze the performance of both serial and parallel applications, via a graphical user interface. Xprofiler provides quick access to the profiled data, so that the functions that are the most CPU-intensive can be easily identified.

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