Loops are slow inside spmd blocks!!

Hi, Can anybody explain what's happening here:

spmd(0) for i=1:100000000,end end

is supposed to run the code on the client. This on most systems is 22 times slower than:

for i=1:100000000, end

without the spmd. However,if you take the loop and put it in a function like:

spmd (0) testfun; end

function testfunc for i=1:100000000,end end

it runs the same speed without spmd. This is quite puzzling.

Answer 1

[Sarah Wait Zaranek]

Looks like loops inside parfor/spmd with tons of iterations are not getting all the benefit from JIT (Just-in-Time interpreter/compiler) which allows for-loops to run faster and not be interpreted very single time step.

I have seen this happen before mostly with cases like this - with many, many iterations of a very simple loop.

To force the JIT into action, the appropriate work-around is to put it in a function - as you have done here.