Difference between revisions of "Guide:TAUChapel"
| Line 15: | Line 15: | ||
c = 0; | c = 0; | ||
forall i in 1..n { | forall i in 1..n { | ||
| − | if | + | if (x ** 2 + y ** 2 <= 1) then |
c += 1; | c += 1; | ||
} | } | ||
| Line 22: | Line 22: | ||
} | } | ||
| − | Notice that the '''forall''' here will compute each iteration in parallel, hence the need to define variable '''c''' as a '''sync''' variable. | + | 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 === | === 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 : int; | ||
| + | for 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 === | === Reduction === | ||
Revision as of 03:58, 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 : int;
for 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;
}
