Lab 4: Optimization and OpenMP Solution

In this lab assignment, you will improve the performance of existing code using optimization

techniques and parallelization using OpenMP. Lab4 handout is located in lnxsrv02 at

 

 

/space/CS33/14S/submission_sp14/lab4_handout

You must log in lnxsrv02 server to get the lab4 handout. Check the tutorial in page 5~6. The lab4 handout contains the following files:

func.h            Header with function prototypes.

func.c            Primary source file (modify the code and submit it).

main.o            Object file containing main() and initialization code.

main_omp.o        Object file for OPENMP

Makefile          Build script.

compare           Directory for compare files. dump              Directory for output files submit            Script to submit a source file.

status            Script to check submission status.

results           Script to check submission results.

clear             Script to clear submission in progress.

 

 

func.c file consists of five functions, and each function consists of some for-loops. Your job is to try to optimize the given code and extract parallelism from the code using OpenMP.

 

 

Grading

         To get any credit,

o Your code should produce the same result as the original code.

o Your code should provide 4X speedup at least.

         For full credit, you should achieve a more than 16X speedup.

         Extra credit can be awarded for speedup beyond that amount.

 

Compiling and Running

To compile sequential executable:                  make seq

To compile with OpenMP enabled:                 make omp

To compile using a different source file:          make omp SRC=func_rev.c

To compile with gprof enabled:                     make seq GPROF=1

To check that your output is correct:              make check

To remove the executable and output files:      make clean

 

         The generated executable is named lab4_seq or lab4_omp.

         The OpenMP version (lab4_omp) is set to use 8 threads.

         The grading server uses 20 threads in the measurement.

         You cannot run the executable in lnxsrv02 server.

         You should use other seasnet servers to run the executables (lnxsrv01, 03, 04, 05, 06,

07, 08). Or you can use your own Ubuntu machine.

     Run “make check” to make sure your code is correct. If you code is correct, then it shows nothing. If you code is incorrect, then it shows which function output is different (wrong).

 

 

Profiling

When optimizing a large program, it is useful to profile it to determine which portions

take up the largest portion of the execution time. There is no point in optimizing code that only takes up a small fraction of the overall computations.

gprof is a simple profiling tool which works with gcc to give approximate statistics on how often each function is called. gprof works by interrupting your program at fixed time intervals and noting what function is currently executing.

As shown earlier, to compile with gprof support, simply add GPROF=1 to the make command. Then when you run the executable, it will produce the file gmon.out containing the raw statistics. To view the statistics in a readable format, run gprof with the name of the executable. Ex) gprof lab4_seq

 

Submission

To use the submission scripts, you must be logged in to lnxsrv02.

 

 

To submit a source file:                                          ./submit func.c

Your unique cookie will be printed to allow you to identify your submissions.

 

 

To check the status of submissions in progress:          ./status

You are limited to 1 submission in progress at a time.

 

 

To check the results of completed submissions:          ./results YOUR_COOKIE

It shows your last three submission results (speedup). For example, a score of 4.0 means your submission improves the performance by 4.0X.

From all your submissions, the “Best” score is considered as your score. You can also check your scores in the web scoreboard.

 

 

To clear the processing submission:     ./clear

It clears your submission in progress. A cleared submission generates RUN_FAILURE error.

 

 

If your submission is delivered to the auto-grading server and your submission is correct, then it shows a number as the speedup. Otherwise, it shows the following ERRORs: COMPILATION_FAILURE        It fails to compile your submission.

  See if your code passes “make omp”

INCORRECT_OUTPUT            Your submission generates the incorrect output.

  See if the result with “./lab4_omp; make check”

TIMEOUT                            It takes too much time to run your submission. SERVER_FULL                       The submission queue in the server is full. RUN_FAILURE                      Unexpected Runtime Error or submission is cleared UNDEFINED_FAILURE             Unexpected Error

 

 

Scoreboard http://www.seas.ucla.edu/~hyunk/cs33/lab4.html http://www.seas.ucla.edu/~hyunk/cs33/lab4_ranking.html

 

Note:

         Measurement Variable: there can be a variation in the performance measurement.

The grading system is designed to minimize the variation, but send me email if you experience a large variation (e.g., more than 5%).

     Server Maintenance: submission might be disabled for the server maintenance. The maintenance schedule is during the class (12 to 2pm) on 5/18, 5/23, and 5/25. However, there could be unscheduled maintenance.

     It may take from 10s seconds to about 30 minutes to process your submission depending on the workload (queuing submissions) in the auto-grading server.

         Initially, 60-sec time gap is set between your submissions. If the number of submission

surges, then the time gap can be increased. The status and clear script reset the time gap.

     If the clear script does not work and you status keeps saying your submission “being processed : 1” more than an hour, then send me your cookie number via email.

o Email address:  roykim78@cs.ucla.edu

o Subject: Lab4 submission stuck

o “Your cookie number”

     “make check” command does not check all the output values. It does the checksum and sampled output comparison to reduce the size of comparison and dump files. It is possible (still unlikely) that you pass  make check, but the submission result is

“INCORRECT_OUTPUT”. Send an email if you experience this issue.

         If there is any other trouble in submission, then send an email.

 

Measuring Environment

Your submission will be compiled with OpenMP and will be run in Xeon E5-2650 v3 Processor with 20 threads. The table below show the CPU specification.

 

Xeon E5-2650 v3
# of Cores
10
# of Threads
20
Processor Base Frequency
2.3 GHz
Max Turbo Frequency
3 GHz
L1 Cache
10 x 32 KB 8-way set assoc.
L2 Cache
10 x 256 KB 8-way set assoc.
L3 Cache
25 MB shared cache

 

Tutorial

# - comments

1. Getting lab4 handout in lnxsrv02 server

bash-4.3$ ssh your_id@lnxsrv02.seas.ucla.edu

bash-4.3$ cp -r /space/CS33/14S/submission_sp14/lab4_handout . bash-4.3$ cd lab4_handout

bash-4.3$ make

gcc -o lab4_seq -O3 -lm main.o func.c

 

#Cannot run the executable in lnxsrv02

bash-4.3$ ./lab4_seq

Do not run lab4 in lnxsrv02 server!

 

bash-4.3$ make omp

gcc -o lab4_omp -O3 -lm -DOPENMP  -fopenmp main_omp.o func.c

 

#Cannot run the executable in lnxsrv02

bash-4.3$ ./lab4_omp

Do not run lab4 in lnxsrv02 server!

 

 

2. Compile or Run the executable in lnxsrv0X server (0X is 01~08 except 02)

bash-4.3$ ssh your_id@lnxsrv01.seas.ucla.edu bash-4.3$ cd lab4_handout

bash-4.3$ make

gcc -o lab4_seq -O3 -lm main.o func.c

 

#run the executable and check its correctness

#the output shows each function’s execution time, total execution time, and a sum of all function’s execution time (Main Secs).

bash-4.3$ ./lab4_seq ;make check

Initializing

Starting
Compute
 
Fun1...
 
Fun1 =
3.4343
Fun2...
 
Fun2 =
5.4588
Fun3...
 
Fun3 =
3.4812
Fun4...
 
Fun4 =
5.1686
Fun5...
 
Fun5 =
6.7885
Dumping
the results...
Total =
24.663, Main Secs =
24.331
 

bash-4.3$ make omp

gcc -o lab4_omp -O3 -lm -DOPENMP  -fopenmp main_omp.o func.c

 

#omp does not improve performance here because func.c is not parallelized

bash-4.3$ ./lab4_omp ;make check

#Threads= 8

Initializing

Starting
Compute
 
Fun1...
 
Fun1 =
3.4334
Fun2...
 
Fun2 =
5.4507
Fun3...
 
Fun3 =
3.4810
Fun4...
 
Fun4 =
5.1698
Fun5...
 
Fun5 =
6.7697
Dumping
the results...
Total =
24.643, Main Secs =
24.305
 

3. Submit your file in lnxsrv02 server

bash-4.3$ ssh your_id@lnxsrv02.seas.ucla.edu bash-4.3$ cd lab4_handout

 

#submit your func.c, then it returns your cookie

bash-4.3$ ./submit func.c

Waiting for confirmation of submission ... Your cookie: 10269

Submitting your file ...

 

#your submission is processing

bash-4.3$ ./status

Waiting for response ...

Number of jobs submitted by you currently being processed : 1

 

#few minutes later, measurement is finished

bash-4.3$ ./status

Waiting for response ...

Number of jobs submitted by you currently being processed : 0

 

 

#results script returns your speedup

bash-4.3$
./results
10269
 
COOKIE
SCORER
 
OLDEST
OLDER
CURRENT
10269
.99
 
X
.99
.99
 

Tip: It is convenient if you use two ssh terminals: one for submission (lnxsrv02) and one for

run the executable (lnxsrv0X).