## Overview

This directory contains a simple example that sums values in a tree. The example exhibits some speedup, but not a lot, because it quickly saturates the system bus on a multiprocessor. For good speedup, there needs to be more computation cycles per memory reference. The point of the example is to teach how to use the raw task interface, so the computation is deliberately trivial.

The performance of this example is better when objects are allocated by the Threading Building Blocks scalable_allocator instead of the default "operator new". The reason is that the scalable_allocator typically packs small objects more tightly than the default "operator new", resulting in a smaller memory footprint, and thus more efficient use of cache and virtual memory. In addition, the scalable_allocator performs better for multi-threaded allocations.

## Files

SerialSumTree.cpp
  Sums sequentially.
SimpleParallelSumTree.cpp
  Sums in parallel without any fancy tricks.
OptimizedParallelSumTree.cpp
  Sums in parallel, using "recycling" and "continuation-passing" tricks. In this case, it is only slightly faster than the simple version.
common.h
  Shared declarations.
main.cpp
  Driver.
Makefile
  Makefile for building example.

## Directories

msvs
  Contains Microsoft* Visual Studio* 2005 workspace for building and running the example.
xcode
  Contains Xcode* IDE workspace for building and running the example.

## To Build

General build directions can be found here.

## Usage

`tree_sum [-stdmalloc] S N`
  S is the problem size (the number of nodes in the tree). N is the number of threads to be used.
  Passing "-stdmalloc" as the 1st parameter causes the default "operator new" to be used for memory allocations instead of the TBB scalable_allocator.
To run a short version of this example, e.g., for use with Intel® Threading Tools:
  Build a debug version of the example (see the build directions).
  Run it with a small problem size and the desired number of threads, e.g., `tree_sum 100000 4`.

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