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Exercise 1

  • Napisati program koji će računati sumu niza unesenog od strane korisnika.

  • Zadatak riješiti sekvencijalno, a zatim paralelizirati problem koristeći pthread.

  • U izvještaju objasniti kako ste paralelizirali problem, koliko niti je korišteno, te zašto.

Solution

Execute test code with:

gcc main.c parallel.c sequential.c array.c -o main -lpthread && ./main

Reading/generating array

Code responsible for handling array can be found here.

  • Read array from stdin
  • Generate array randomly
  • Print the array

Sequential sum

Code responsible for sequential sum of array elements can be found here.

  • Calculate sum of all elements in array and return the result

Parallelised sum

Code responsible for parallelised sum of array elements can be found here.

  1. Split the array in NUM_THREADS subarrays
  2. Calculate sequential sum of each subarray in threads independetly
  3. Wait till all threads execute and then sum the results
  • Number of threads 2, 4, 8 were tested, and 2 threads had best perfomance.

Results

NUM_THREADS 2

Array Length PARALLEL SEQUENTAL
1 0.000800 s 0.000006 s
10 0.000442 s 0.000007 s
100 0.000480 s 0.000004 s
1000 0.000248 s 0.000008 s
10000 0.000473 s 0.000041 s
100000 0.000740 s 0.000423 s
1000000 0.004281 s 0.004002 s
10000000 0.036420 s 0.039574 s
100000000 0.380668 s 0.383230 s
1000000000 3.424999 s 3.814460 s

NUM_THREADS 4

Array Length PARALLEL SEQUENTAL
1 0.001346 s 0.000003 s
10 0.000741 s 0.000004 s
100 0.000475 s 0.000004 s
1000 0.000432 s 0.000007 s
10000 0.000575 s 0.000049 s
100000 0.000927 s 0.000417 s
1000000 0.004368 s 0.004082 s
10000000 0.044516 s 0.045308 s
100000000 0.359088 s 0.383255 s
1000000000 3.557832 s 3.849736 s

NUM_THREADS 8

Array Length PARALLEL SEQUENTAL
1 0.001610 s 0.000003 s
10 0.001116 s 0.000003 s
100 0.001086 s 0.000004 s
1000 0.000900 s 0.000007 s
10000 0.003290 s 0.000042 s
100000 0.001563 s 0.000397 s
1000000 0.005921 s 0.003818 s
10000000 0.038344 s 0.038660 s
100000000 0.394244 s 0.386456 s
1000000000 3.663846 s 3.875184 s

Issue

Issue, using threads cause only negative efect on perfomance

SEQUENTAL PARALLEL
0.000003 s 0.001128 s
0.009709 s 0.011254 s
0.004552 s 0.005289 s
0.004014 s 0.004898 s
0.041205 s 0.039637 s
0.379131 s 0.392338 s
3.854432 s 3.983880 s

Fix: Calling function from thread is not an option!