Profiling

Kent Milfeld

TACCMay 28, 2009

Outline

• Profiling MPI performance with MPIp• Tau• gprof• Example: matmult

MPIp

• Scalable Profiling library for MPI apps• Lightweight• Collects statistics of MPI functions• Communicates only during report generation • Less data than tracing tools

http://mpip.sourceforge.net

Usage, Instrumentation, Analysis• How to use

– No recompiling required!– Profiling gathered in MPI profiling layer

• Link static library before default MPI libraries -g -L${TACC_MPIP_LIB} -lmpiP -lbfd -liberty -lintl –lm

• What to analyze– Overview of time spent in MPI communication during the

application run– Aggregate time for individual MPI call

Control• External Control: Set MPIP environment variable (threshold,

callsite depth)– setenv MPIP ‘-t 10 –k 2’– export MPIP= ‘-t 10 –k 2’

• Use MPI_Pcontrol(#) to limit profiling to specific code blocks

Pcontrol Arg Behavior

0 Disable profiling.

1 Enable Profiling.

2 Reset all callsite data.

3 Generate verbose report.

4 Generate concise report.

MPI_Pcontrol(2);MPI_Pcontrol(1); MPI_Abc(…);MPI_Pcontrol(0);

call MPI_Pcontrol(2)call MPI_Pcontrol(1) call MPI_Abc(…)call MPI_Pcontrol(0)

F90

C

• Untar the mpip tar file. % tar -xvf ~train00/mpip.tar; cd mpip• Read the “Instructions” file– setup Env. with sourceme-files% source sourceme.csh (C-type shells)% source sourceme.sh (Bash-type shells)

Example

module purge {Resets to default modules.}module load TACCmodule unload mvapich {Change compiler/MPI to intel/mvapich.} module swap pgi intelmodule load mvapich

module load mpiP {Load up mpiP.}

set path=($path /share/home/00692/train00/mvapich1_intel/Mpipview_2.02/bin){Sets PATH with mpipview dir. – separate software from mpiP.)}

• Compile either the matmultc.c or matmultf.f90 code.

% make matmultfOr

% make matmultc

• Uncomment “ibrun matmultc” or “ibrun matmultf” in the job file.

• Submit job.% qsub job

• Results in:<exec_name><unique number>.mpiP

Example (cont.)

Example *.mpiP Output

• MPI-Time: wall-clock time for all MPI calls

• MPI callsites

Output (cont.)

• Message size

• Aggregate time

e.g. % mpipview matmultf.32.6675.1.mpiPNote: list selection.

mpipview

Indexed

Call Sites

Statistics

Message Sizes

Tau Outline

• General– Measurements– Instrumentation & Control– Example: matmult

• Profiling and Tracing– Event Tracing– Steps for Performance Evaluation– Tau Architecture

• A look at a task-parallel MxM Implementation• Paraprof Interface

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General

• Tuning and Analysis Utilities (11+ year project effort)

www.cs.uoregon.edu/research/paracomp/tau/

• Performance system framework for parallel, shared & distributed memory systems

• Targets a general complex system computation model– Nodes / Contexts / Threads

• Integrated toolkit for performance instrumentation, measurement, analysis, and visualization

TAU = Profiler and Tracer + Hardware Counters + GUI + Database

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Tau: Measurements• Parallel profiling

– Function-level, block (loop)-level, statement-level– Supports user-defined events– TAU parallel profile data stored during execution– Hardware counter values– Support for multiple counters– Support for callgraph and callpath profiling

• Tracing– All profile-level events– Inter-process communication events– Trace merging and format conversion

17

PDT is used to instrument your code.

Replace mpicc and mpif90 in make files with tau_f90.sh and tau_cc.sh

It is necessary to specify all the components that will be used in the instrumentation (mpi, openmp, profiling, counters [PAPI], etc. However, these come in a limited number of combinations.)

Combinations: First determine what you want to do (profiling, PAPI counters, tracing, etc.) and the programming paradigm (mpi, openmp), and the compiler. PDT is a required component:

Tau: Instrumentation

PAPICallpath

…

MPIOMP

…

intelpgignu

PDTHand-code

Collectors Compiler:ParallelParadigmInstrumentation

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You can view the available combinations(alias tauTypes 'ls -C1 $TAU | grep Makefile ' ).

Your selected combination is made known to the compiler wrapper through the TAU_MAKEFILE environment variable.

E.g. the PDT instrumention (pdt) for the Intel compiler (icpc) for MPI (mpi) is set with this command:

setenv TAU_MAKEFILE /…/Makefile.tau-icpc-mpi-pdt

Other run-time and instrumentation options are set through TAU_OPTIONS. For verbose:

setenv TAU_OPTIONS ‘-optVerbose’

Tau: Instrumentation

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% tar –xvf ~train00/tau.tar

% cd tau READ the Instructions file % source sourceme.csh or % source sourceme.sh create env. (modules and TAU_MAKEFILE)

% make matmultf create executable(s)or

% make matmultc

% qsub job submit job (edit and uncomment ibrun line)

% paraprof (for GUI) Analyze performance data:

Tau Example

20

Definitions – Profiling• Profiling

– Recording of summary information during execution• inclusive, exclusive time, # calls, hardware statistics, …

– Reflects performance behavior of program entities• functions, loops, basic blocks• user-defined “semantic” entities

– Very good for low-cost performance assessment– Helps to expose performance bottlenecks and hotspots– Implemented through

• sampling: periodic OS interrupts or hardware counter traps• instrumentation: direct insertion of measurement code

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Definitions – Tracing

TracingRecording of information about significant points (events)

during program executionentering/exiting code region (function, loop, block, …) thread/process interactions (e.g., send/receive message)

Save information in event record timestampCPU identifier, thread identifierEvent type and event-specific information

Event trace is a time-sequenced stream of event records Can be used to reconstruct dynamic program behaviorTypically requires code instrumentation

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Event Tracing: Instrumentation, Monitor, Trace

1 master

2 worker

3 ...

void worker { trace(ENTER, 2);

... recv(A, tag, buf); trace(RECV, A);

... trace(EXIT, 2);

}

void master { trace(ENTER, 1);

... trace(SEND, B);

send(B, tag, buf); ...

trace(EXIT, 1);}

MONITOR58 A ENTER 1

60 B ENTER 2

62 A SEND B

64 A EXIT 1

68 B RECV A

...

69 B EXIT 2

...

CPU A:

CPU B:

Event definition

timestamp

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Event Tracing: “Timeline” Visualization

1 master

2 worker

3 ...

58 A ENTER 1

60 B ENTER 2

62 A SEND B

64 A EXIT 1

68 B RECV A

...

69 B EXIT 2

...

mainmasterworker

58 60 62 64 66 68 70

B

A

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Steps of Performance Evaluation

Collect basic routine-level timing profile to determine where most time is being spent

Collect routine-level hardware counter data to determine types of performance problems

Collect callpath profiles to determine sequence of events causing performance problems

Conduct finer-grained profiling and/or tracing to pinpoint performance bottlenecksLoop-level profiling with hardware countersTracing of communication operations

25

TAU Performance System Architecture

26

Overview of Matmult: C = A x B

CreateA & B

A BC = x

Order NP Tasks

MASTER Worker

Receive B

SendRow of A

Multiply row a x B

Send Back row of C

Receive a

ReceiveRow of C

Send B

jj x=

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Preparation of Matmult: C = A x B

PE 0

CreateA

CreateB

GenerateA & B

BroadcastB to All

by columns

PE 0 PE x

MPI_Bcast( b(1,i)…

loop over i (i=1n)

PE 0

A BC = x

Order NP Tasks

MASTER

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Master Ops of Matmult: C = A x B

Master (0) sends rows 1 through (p-1) to

slaves (1p-1) receives

1

p-1

PE 0 PE 1 -- p-1

MPI_Send(arow … i,i

loop over i (i=1p-1)

destinationtag

Master (0) receives rows 1 through (n) from

Slaves.

1

n

PE 0 PE 1 -- p-1

MPI_Recv(crow … ANY,k

loop over i (i=1n)

source,tag

MPI_Send(arow …idle,jdest,tag

A BC = x

Order NP Tasks

MASTER

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Master Ops of Matmult: C = A x B

Slave(any) sends row j of C to master, PE 0

PE 0 MPI_Send( crow … j

jrow j

Slaves multiply all Columns of B into A (row i) to form row i of Matrix C

x=

Pick up broadcast of B columns from PE 0

MPI_Recv( arow …ANY,j

loop over i (i=1n)

Matrix * Vector

row j

A BC = x

Order NP Tasks

Worker

Slave receives anyA row from PE 0 j

j

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Paraprof and Pprof

• Execute application and analyze performance data:• % qsub job

– Look for files: profile.<task_no>.

– With Multiple counters, look for directories for each counter.

• % pprof (for text based profile display)• % paraprof (for GUI)

– pprof and paraprof will discover files/directories.

– paraprof runs on PCs,Files/Directories can be downloaded to laptop and analyzed there.

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Tau Paraprof Overview

HPMToolkit

MpiP

TAU

Raw files

PerfDMFmanaged(database)

Metadata

Application

Experiment

Trial

32

Tau Paraprof Manager WindowProvides Machine Details

Organizes Runs as: Applications, Experiments and Trials.

33

Routine Time Experiment

Profile Information is in “GET_TIME_OF_DAY” metric

Mean and Standard Deviation Statistics given.

34

Multiply_Matrices Routine Results

not from same run

Function Data Window gives a closer look at a single function:

35

Float Point OPS trial

Hardware Counters provide Floating Point Operations (Function Data view).

36

L1 Data Cache Miss trial

Hardware Counters provide L1 Cache Miss Operations.

37

Call Path

Call Graph Paths (Must select through “thread” menu.)

38

Call Path

TAU_MAKEFILE = …Makefile.tau-callpath-icpc-mpi-pdt

39

Derived MetricsSelect Argument 1 (green ball); Select Argument 2 (green ball);

Select Operation; then Apply. Derived Metric will appear as a new trial.

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DerivedMetrics

Be careful even thoughratios are constant, coresmay do different amounts

of work/operations per call.

Since FP/Missratios are

constant– mustbe memory

access problem.

GPROF

GPROF is the GNU Project PROFiler. gnu.org/software/binutils/

•Requires recompilation of the code.

•Compiler options and libraries provide wrappers for each routine call, and periodic sampling of the program.

•A default gmon.out file is produced with the function call information.

•GPROF links the symbol list in the executable with the data in gmon.out.

Types of Profiles

• Flat Profile– CPU time spend in each function (self and cumulative) – Number of times a function is called– Useful to identify most expensive routines

• Call Graph– Number of times a function was called by other functions– Number of times a function called other functions– Useful to identify function relations– Suggests places where function calls could be eliminated

• Annotated Source– Indicates number of times a line was executed

Profiling with gprofUse the -pg flag during compilation:% gcc -g -pg srcFile.c% icc -g -pg srcFile.c% pgcc -g -pg srcFile.c

Run the executable. An output file gmon.out will be generated with the profiling information.

Execute gprof and redirect the output to a file:% gprof exeFile gmon.out> profile.txt% gprof -l exeFile gmon.out> profile_line.txt% gprof -A exeFile gmon.out>profile_anotated.txt

gprof example

Move into the profiling examples directory:

% cd profile/

Compile matvecop with the profiling flag:

% gcc -g -pg -lm matvecop.c {@ ~train00/matvecop.c}

Run the executable to generate the gmon.out file:

% ./a.out

Run the profiler and redirect output to a file:

% gprof a.out gmon.out > profile.txt

Open the profile file and study the instructions.

Visual Call Graph

mainmain

matSqrtmatSqrt

vecSqrtvecSqrt

matCubematCube vecCubevecCubesysSqrtsysSqrt sysCubesysCube

Flat profile

In the flat profile we can identify the most expensive parts of the code (in this case, the calls to matSqrt, matCube, and sysCube).

% cumulative self self total

time seconds seconds calls s/call s/call name

50.00 2.47 2.47 2 1.24 1.24 matSqrt

24.70 3.69 1.22 1 1.22 1.22 matCube

24.70 4.91 1.22 1 1.22 1.22 sysCube

0.61 4.94 0.03 1 0.03 4.94 main

0.00 4.94 0.00 2 0.00 0.00 vecSqrt

0.00 4.94 0.00 1 0.00 1.24 sysSqrt

0.00 4.94 0.00 1 0.00 0.00 vecCube

Call Graph Profileindex % time self children called name

0.00 0.00 1/1 <hicore> (8)

[1] 100.0 0.03 4.91 1 main [1]

0.00 1.24 1/1 sysSqrt [3]

1.24 0.00 1/2 matSqrt [2]

1.22 0.00 1/1 sysCube [5]

1.22 0.00 1/1 matCube [4]

0.00 0.00 1/2 vecSqrt [6]

0.00 0.00 1/1 vecCube [7]

-----------------------------------------------

1.24 0.00 1/2 main [1]

1.24 0.00 1/2 sysSqrt [3]

[2] 50.0 2.47 0.00 2 matSqrt [2]

-----------------------------------------------

0.00 1.24 1/1 main [1]

[3] 25.0 0.00 1.24 1 sysSqrt [3]

1.24 0.00 1/2 matSqrt [2]

0.00 0.00 1/2 vecSqrt [6]

-----------------------------------------------

Profiling dos and don’ts

DO

• Test every change you make

• Profile typical cases• Compile with

optimization flags• Test for scalability

DO NOT

• Assume a change will be an improvement

• Profile atypical cases• Profile ad infinitum

– Set yourself a goal or– Set yourself a time limit

PAPI Implementation

Tools

PAPI Low LevelPAPI High Level

Hardware Performance Counter

Operating System

Kernel Extension

PAPI Machine Dependent SubstrateMachine

SpecificLayer

PortableLayer

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PAPI Performance Monitor

• Provides high level counters for events:– Floating point instructions/operations, – Total instructions and cycles– Cache accesses and misses– Translation Lookaside Buffer (TLB) counts– Branch instructions taken, predicted, mispredicted

• PAPI_flops routine for basic performance analysis– Wall and processor times– Total floating point operations and MFLOPS http://icl.cs.utk.edu/projects/papi

• Low level functions are thread-safe, high level are not

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High-level API

• C interfacePAPI_start_countersPAPI_read_countersPAPI_stop_countersPAPI_accum_countersPAPI_num_countersPAPI_flips PAPI_ipc

• Fortran interfacePAPIF_start_countersPAPIF_read_countersPAPIF_stop_countersPAPIF_accum_countersPAPIF_num_countersPAPIF_flipsPAPIF_ipc

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Instrumenting Code:1.) Specify “events” in an array.2.) Initialize library.3.) Start counting events.4.) Stop counting (and accumulate).