Guide:TAUChapel

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Line 33: Line 33:
proc compute_pi(p_x: [] real(64), p_y: [] real(64)) : real { proc compute_pi(p_x: [] real(64), p_y: [] real(64)) : real {
- var c : int;+ var c : sync int;
- for i in in_circle(p_x, p_y) {+ forall i in in_circle(p_x, p_y) {
c += i; c += i;
} }
Line 47: Line 47:
=== Reduction === === Reduction ===
 +
 +Furthermore with reorganization will allow us to take advantage of Chapel's built in reduction:
 +
 + proc compute_pi(p_x: [] real(64), p_y: [] real(64)) : real {
 +
 + var c : int;
 + c= +reduce in_circle(p_x, p_y);
 + return c * 4.0 / n;
 +
 + }
=== Multiple Locals === === Multiple Locals ===
=== Performance Results === === Performance Results ===

Revision as of 04:26, 30 September 2013

Contents

Chapel

MonteCarlo example

To test out some Chapel's language features let program a MonteCarlo simulation to calculate PI. We can calculate PI by assess how many points with coordinates x,y fit in the unit circle, ie x^2+y^2<=1.

Basic

Here is the basic routine that computes PI:

proc compute_pi(p_x: [] real(64), p_y: [] real(64)) : real {

 var c : sync int;
 c = 0;
 forall i in 1..n {
   if (x ** 2 + y ** 2 <= 1) then
       c += 1;
 }
 return c * 4.0 / n;

}

Notice that the forall here will compute each iteration in parallel, hence the need to define variable c as a sync variable. Performance here is limited by the need to synchronize access to c. Take a look of this profile:


X% percent of the time is spent in synchronization. Let's see if we can do better.

Procedure promotion

Only feature of Chapel is procedure promotion where calling a procedure that takes scalar arguments with an array, the procedure is called for each element of the array in parallel:

proc compute_pi(p_x: [] real(64), p_y: [] real(64)) : real {

 var c : sync int;
 forall i in in_circle(p_x, p_y) {
   c += i;
 }
 return c * 4.0 / n;

}
proc in_circle(x: real(64), y: real(64)): bool
{
  return (x ** 2 + y ** 2) <= 1;
}

Reduction

Furthermore with reorganization will allow us to take advantage of Chapel's built in reduction:

proc compute_pi(p_x: [] real(64), p_y: [] real(64)) : real {

 var c : int;
 c= +reduce in_circle(p_x, p_y);
 return c * 4.0 / n;

}

Multiple Locals

Performance Results

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