Thread: Prefechind data from main memory into cache

I have a huge program which do a lot of different tasks. There are hundreds, and one of them is Transposition Table access. This TT is very big, and I access it from time to time to retrieve a cell of around 8 or 10 ints size.

As my program has to be tuned for speed I have used a _mm_prefetch intrinsic instruction for trying to prefetch data a few instruction before real call.

I have trying to measuring time doing differents test but I have not get any improvement, so I ask myselft if I have programmed the code well.

Is there any way of knowing if the data have move into cache after the prefetch? .... or is there any way of knowing if _mm_prefecth instructions has been sucessfull?

My code is near like this:

Code:

	unsigned int nt = n->hash & total_hash_entries;
	t_entrada_hash *p = &ptrTT[nt];

        _mm_prefetch((char*) p, _MM_HINT_NTA)

        .... a few lines of code here.....

	use of p.... i.e.:
        if (p->x = z...)

Originally Posted by Codeplug

What makes you think a change in CPU cache usage will provide any speed-up?
gg

well, commmon sense: if can prefetch data into cache a hundreds instructions before use them, I will have a few cycles gain.