what is unrolled loops and how to check and know unrolled loops of cpu in ubuntu

zerop · 07-21-2014, 11:15 PM

If memory access were 100 cycles, and the unrolled loops are two cycles apart, LookAhead could be set to 50

it seems prefetch lookahead is (memory access)/(unrolled loops)

how to check how many cycles in memory access?
how to check how many unrolled loops ?

sag47 · 07-25-2014, 05:07 PM

Loop unrolling is a compiler optimization technique. It is not a setting in your OS. If you know the settings you want in software then you can set the optimizations at compile time.

What is the actual problem you're trying to solve? Give the overall explanation of your problem and don't ask about sub-parts.

dugan · 07-25-2014, 05:10 PM

Quote:

Originally Posted by zerop

if ... and the unrolled loops are two cycles apart

Where did that huge if come from?

I googled your assumption and got:

http://stackoverflow.com/a/19749677

Which doesn't make your question clearer.

Maybe it would help if you tell us why you're asking the question?

Quote:

how to check how many unrolled loops ?

Sorry, but I'm going to have to give the obvious answer here. You dissassemble the program and examine the assembly.

zerop · 07-27-2014, 12:31 AM

this stackoverflow is question is what i search come from

however it do not answer unrolled loops

sundialsvcs · 07-31-2014, 10:22 PM

The very-simple essential idea of "loop unrolling" is that ... sometimes, the conditional-instructions that send the computer back into another iteration of a loop are expensive, whereas the instructions that make up the body of the loop are not. Therefore, if (for example) you know that the loop will be executed some multiple-of-three times, it might be faster to generate three instances of the loop-body in a row, then have the loop execute one-third as many times. It's a compiler optimization, in the classic "speed vs. space" tradition.