why parfor-loop spend more time for-loop?

function test_parfor
N = 1e8;
sum_all = 0; % sum all numbers
sum_odd = 0; % sum odd numbers
sum_even = 0; % sum even numbers

tic;
parfor i = 1 : N
  sum_all = sum_all + i; % sum all numbers
  if mod(i,2)
      sum_odd = sum_odd + i; % sum odd numbers
  else
      sum_even = sum_even + i; % sum even numbers
  end %endif
end %endfor
toc;

fprintf('sum_all=%d,\nsum_odd=%d,\nsum_even=%d.\n', ...
    sum_all, sum_odd, sum_even);

I have initialized the parpool envionment and run the codes above. However, the parfor-loop took far more time than single for-loop. Why? What is wrong with my codes? Thank you very much! :-)

Answer 1

[Matt J]

Did you execute it in a script or a function? Try the latter.

[Tao]

I have tried the function form, but get the same result. parfor-loop take far more time than for-loop. If the If-bloack in the parfor-loop is removed, the time of it will less than the one of single for-loop.

[Matt J]

How many cores on your machine? And how many workers in your parpool?

[Tao]

Thank you for your reply. The numCores of my PC is 12. I initialize 12 workers.