Sequential and parallel execution of Bernstein's condition.

Posted on 2005-05-07
Last Modified: 2009-07-29
I am having a doubt in understanding an example explained by Bernstein for sequential and parallel execution order .

given was
S1 : A =B+C ,S2 : L=D+E, S3: F=G+E,S4 : C=A+F,S5 : M =G+C,S6 : A= L+C ,S7 : A= E+A.
for S1 when B and C are given as  inputs and A .
parallel : S1,S2,S3,S5  can be executed parallely
sequential ; after S1 is executed the out put (A) is taken as the input to S4 and S7 .
and my question is when S4 is executed we get the output as C which is given as input to S5 S1and S6 so how is S4 dependent on S1.
bcoz to execute S1 we need to execute S4 but S4 as the input A .Here there is an access conflict  taking place can anyone  explain me this clearly as how will the parallel and sequential execution take place.
As when i am trying to understand the logic i am able to c more acess conflicts taking place in this execution place.
Question by:anumit
    LVL 31

    Accepted Solution

    The statements are considered as a sequence of  sequential statements

    S1 : A =B+C
    S2 : L=D+E
    S3: F=G+E
    S4 : C=A+F
    S5 : M =G+C
    S6 : A= L+C
    S7 : A= E+A.

    and can be rewritten as a dependency graph as

                   S1             S2
                    |               |
                    |               |
                    |               |
                    |               |
                   S5             S7
    LVL 31

    Expert Comment

    ..vertical lines have downward direction
    LVL 31

    Expert Comment

    A simple parallelisation would be

    (1) S1 S2 S3
    (2) S4
    (3) S5 S6
    (4) S7

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