Re: [boost] [Parallel Algorithms] Queries regarding the Boost.Thread / Parallel algorithms

Subject: Re: [boost] [Parallel Algorithms] Queries regarding the Boost.Thread / Parallel algorithms
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2014-03-21 17:05:55

Le 20/03/14 21:57, Naveen a écrit :
> Hi,
Hi,
> Based on understanding the proposal, I'm just curious to know how we are
> gonna use the compiler optimizations when creating the parallel_xxx
> functions. Say any normal loop would be optimized by the compiler using any
> of the loop transformations like loop interchange, loop unrolling, loop
> fusion etc.,
>
> let us consider a sample FORTRAN code to :
>
> DO J = 1, 100
>    DO I = 1, 100
>      DO K = 1, 100
>         C(I,J) = C(I,J) + A(I,K) * B(K,J)
>      END DO
>    END DO
> END DO
>
>
> which may or may not be optimized by the compiler into something like this
>
> DO K = 1, 100
>    DO I = 1, 100
>      DO J = 1, 100
>         C(I,J) = C(I,J) + A(I,K) * B(K,J)
>      END DO
>    END DO
> END DO
>
> so, when we try to introduce our parallel algorithm in to the loop
> containing J, it may be interchanged depending upon the compiler
> properties. So, should we plan for such scenarios.
Could you show how would you parallelize this code?
> When we try to introduce our parallel functions the only way possible is to
> make the compiler optimizations temporarily inactive on those tasks. But,
> by doing so the performance of the application will be affected.
>
> Should we really tackle this scenario or am i looking into a completely
> irrelevant picture?
>
>
I don't see nothing irrelevant.

Vicente