PfHP Lots of loops to parallelize

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Unit 4.3.1 Lots of loops to parallelize

Let's again consider the five loops around the micro-kernel:

What we notice is that there are lots of loops that can be parallelized. In this section we examine how parallelizing each individually impacts parallel performance.

Homework 4.3.1.1.

In directory Assignments/Week4/C, execute

export OMP_NUM_THREADS=1
make Five_Loops_Packed_8x6Kernel

to collect fresh performance data. In the Makefile, MC and KC have been set to values that yield reasonable performance in our experience. Transfer the resulting output file (in subdirectory data) to Matlab Online Matlab Online and test it by running

Plot_MT_Performance_8x6.mlx

If you decide also to test a 12x4 kernel or others, upload their data and run the corresponding Plot_MT_Performance_??x??.mlx to see the results. (If the .mlx file for your choice of \(m_R \times n_R \) does not exist, you may want to copy one of the existing .mlx files and do a global search and replace.)

Solution

On Robert's laptop:

This reminds us: we are doing really well on a single core!

Remark 4.3.1.

Here and in future homework, you can substitute 12x4 for 8x6 if you prefer that size of micro-tile.

Remark 4.3.2.

It is at this point in my in-class course that I emphasize that one should be careful not to pronounce "parallelize" as "paralyze." You will notice that sometimes if you naively parallelize your code, you actually end up paralyzing it...