DidaWiki

Lab time 06/05/2016

• You can download current TBB on ottavinareale with

wget https://www.threadingbuildingblocks.org/sites/default/files/software_releases/linux/tbb44_20160413oss_lin.tgz

• Install TBB in your home directory on ottavinareale by unpacking the archive
• Set up your install dir of TBB inside the tbbvars.sh script or tbbvars.csh (depending on your shell)
• call tbbvars.sh intel64 linux from your shell profile script

Compute the Mandelbrot set like in the MPI lab farm exercise. Program parameters define a square n*n (or rectangular n*m) subset of the complex plane, the number of samples i,j for each coordinate, the max number of iterations per point MaxI.

The first exaple will not really be a farm: generate the input stream of points with a parallel for (either two nested or a single one with a 2D range). You will need to create appropriate range(s) for that.

The computation for each point is actually given by the mandelbrot function, which returns the number of iteration until the point diverges, or MaxI if the limit is exceeded.

Choose a plane region near the border of the mandelbrot set and getting some of the points of the set.

• measure the execution time and the speedup which varies with the iteration limit parameter;
• check what is the amount of parallelism choose by TBB
• check if the load is balanced
• check if you need to tune the grain size in order to achieve a good speedup when MaxI is low.
• try choosing a different amoutn of parallelism

Can you dynamically optimize the grain according to the input parameters?

• decide how you will provide the sequntial mandelbrot function as loop body (via lambda or via a loop body class with () operator)
• decide if you want to set up two nested parallel_for loops or a single loop with a 2D range (it is useful to try both and compare)