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

Subject: Re: [boost] [Parallel Algorithms] Queries regarding the Boost.Thread / Parallel algorithms
From: Naveen (nravichandrasekaran_at_[hidden])
Date: 2014-03-20 16:57:31

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.

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?

Regards,

*NAVEEN*
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