Tweak binarytrees-pool based on feedback (#26009)

Tweak `binarytrees-pool` based on feedback. Many of the changes are
cosmetic (changing how constants are written) and others improve the
portability (making sure enough memory is available when running with
limited cores).

[Reviewed by @bradcray]

test/studies/shootout/binary-trees/binarytrees-pool.chpl

@@ -6,46 +6,48 @@
      Brad Chamberlain
 */
 
-use Allocators;
+use Allocators, Math;
 
-config const n = 10,         // the maximum tree depth
-             globalPoolSize = (2 ** 31)-1,
-             localPoolSize = globalPoolSize;
-
-var globalPool = new bumpPtrMemPool(globalPoolSize, alignment=0);
+config const n = 10;                         // the maximum tree depth
 
 proc main() {
-  const minDepth = 4,                      // the shallowest tree
-        maxDepth = max(minDepth + 2, n),   // the deepest normal tree
-        strDepth = maxDepth + 1,           // the depth of the "stretch" tree
-        depths = minDepth..maxDepth by 2;  // the range of depths to create
-  var stats: [depths] (int,int);           // stores statistics for the trees
+  const minDepth = 4,                        // the shallowest tree
+        maxDepth = max(minDepth + 2, n),     // the deepest normal tree
+        strDepth = maxDepth + 1,             // the depth of the "stretch" tree
+        depths = minDepth..maxDepth by 2,    // the range of depths to create
+        nodeSize = 24;                       // the size of a node
+  var stats: [depths] (int,int);             // stores statistics for the trees
+
+  inline proc poolSize(depth, num=1) do return num*2**(depth+1)*nodeSize;
 
   //
   // Create the short-lived "stretch" tree, checksum it, and print its stats.
   //
   {
-    const strTree = newWithAllocator(globalPool, unmanaged Tree, strDepth, globalPool);
+    const pool = new bumpPtrMemPool(poolSize(strDepth), alignment=0),
+          strTree = newWithAllocator(pool, unmanaged Tree, strDepth, pool);
     writeln("stretch tree of depth ", strDepth, "\t check: ", strTree.sum());
   }
 
   //
   // Build the long-lived tree.
   //
-  const llTree = newWithAllocator(globalPool, unmanaged Tree, maxDepth, globalPool);
+  const pool = new bumpPtrMemPool(poolSize(maxDepth), alignment=0),
+        llTree = newWithAllocator(pool, unmanaged Tree, maxDepth, pool);
 
   //
   // Iterate over the depths. At each depth, create the required trees in
   // parallel, compute their sums, and free them.
   //
   for depth in depths {
-    const iterations = 2**(maxDepth - depth + minDepth);
+    const iterations = 2**(maxDepth - depth + minDepth),
+          ps = poolSize(depth, divCeilPos(iterations, here.maxTaskPar));
     var sum = 0;
 
-    forall i in 1..iterations
+    forall 1..iterations
       with (+ reduce sum,
-            var localPool = new bumpPtrMemPool(localPoolSize, alignment=0)) {
-      const t = newWithAllocator(localPool, unmanaged Tree, depth, localPool);
+            var pool = new bumpPtrMemPool(ps, alignment=0)) {
+      const t = newWithAllocator(pool, unmanaged Tree, depth, pool);
       sum += t.sum();
     }
     stats[depth] = (iterations, sum);

test/studies/shootout/binary-trees/binarytrees-pool.execenv

@@ -0,0 +1,2 @@
+# this value has been shown to cause the most problems for this test
+CHPL_RT_NUM_THREADS_PER_LOCALE=3