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ashleydavies / hpce-2018-cw5

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The deadline for this assignment is

22:00 Mon 4 Mar 2019

Code infrastructure

This repository contains a simple framework for describing and executing small computational puzzles. Each puzzle is derived from puzzler::Puzzle, which provides a number of methods for creating inputs, executing puzzles, and checking outputs. Of particular interest to you is the puzzler::Puzzle::Execute method, which is the method that you need to accelerate, and is the function that is timed for performance purposes. Each input problem has an associated "scale", which is a measure of computational complexity - in general, as the scale number goes up, the problem will take longer.

There are four puzzles that you need to work on as a pair:

  • ising
  • rank
  • decompose
  • integral

Each puzzle represents the computational core of some common calulation, though all have been simplified to just a few lines of code. It's not too difficult to work out what the underlying application is, and you may find it interesting to look at existing solutions in the literature. However, no specialised knowledge of each puzzles application domain is needed, and the expectation is that only the standard techniques from the lectures and earlier courseworks are needed.

The repository has a number of different directories:

  • The directories under include should not be modified.

    • They are owned by the framework, and will be over-written in assessment environments to ensure they have not been modified.
    • If there are any changes to these files in the spec then they will be done in an additive way wherever possible (no changes are expected).

  • You own the files in the provider directory

    • You'll be replacing the implementation of XXXXProvider::Execute in provider/xxxx.hpp with something (hopefully) faster.
    • A good starting point is to replace the implementation of XXXXProvider::Execute with a copy of the body of XXXXPuzzle::ReferenceExecute, and check that it still does the same thing.
    • The reason for the indirection is to force people to have an unmodified reference version available at all times, as it tends to encourage testing.
    • You can have multiple live alternative engines for each puzzle compiled into the executable, allowing you to progressively refine solutions while keeping previous known-good versions around. Each version should be registered under a different engine name.

  • The public entry point to your code is via puzzler::PuzzleRegistrar::UserRegisterPuzzles, which must be compiled into the static library lib/libpuzzler.a.

    • Clients will not directly include your code, they will only #include "puzzler/puzzles.h, then access puzzles via the registrar. They will get access to the registrar implementation by linking against lib/libpuzzler.a.
    • Note: If you do something complicated in your building of libpuzzler, it should still be possible to build it by going into provider and calling make all.
    • The current working directory during execution will be the root of the repository. So it will be executed as if by typing bin/execute_puzzle, and an opencl kernel should be loaded using the relative path provider/my_kernel.cl.
    • Programs which link against and use lib/libpuzzler.a will also link in TBB and OpenCL.
    • You can register a given implementation with the registrar under a chosen engine name. This allows you to have multiple versions of a puzzle solution available, and allows you to expose specific solutions for different deliverable components.

  • The programs in src have no special meaning or status, they are just example programs

The reason for all this strange indirection is that I want to give maximum freedom for you to do strange things within your implementation (example definitions of "strange" include CMake) while still having a clean abstraction layer between your code and the client code.

Deliverables

The deliverable sections are:

  • TBB Competence (20%)

    • For all puzzles, you must deliver a version which correctly uses TBB to solve the problem. The majority of the compute must be performed under TBB, and it should use multiple cores. However, performance is not considered for this part, only correctness.

    • The engines demonstrating competence should be exposed via the name ${puzzle}.tbb, where <puzzle> is the puzzle name. For example ising.tbb or rank.tbb.

  • OpenCL Competence (20%)

    • For two puzzles you must deliver a version which correctly uses OpenCL to solve the problem. The majority of the compute must be performed in kernels, and it should use multiple work-items in parallel. Again, performance is not considered here, only correctness.

    • The puzzles demonstrating OpenCL competence should be exposed via the name ${puzzle}.opencl.

    • If there are more than two engines listed of the form ${puzzle}.opencl then two will be selected in a deterministic way.

  • Performance optimisation (40%)

    • Each puzzle has two target performance metrics (see below), defined for a competent and expert person, which were based on a person at the given level spending three hours per puzzle. For each puzzle you should provide an optimised version, and the improvement relative to the reference will be mapped to a mark:

      • [reference,competent) : 0..40%
      • [competent,expert*0.9) : 40..100%

      Matching (or exceeding) expert*0.9 is equivalent to getting full marks, though you are not time constrained.

    • The puzzles to be assessed for performance should have a name of the form ${puzzle}.opt.

    • The target environment is a g3.4xlarge instance, running the HPCE-2018 AMI.

    • There is no requirement on how the optimised engines are implemented. You could use OpenCL, TBB, a combination of OpenCL and TBB, or even straight sequential code.

    • The engines selected here might be aliases for engines from the competence sections, or they could be completely different.

  • Results presentation (20%)

    • Produce an A4 pdf called question/results.pdf which uses empirical data to explore and answer a question that arose while working with the puzzles. The pdf should contain no more than 300 words of text, and should use empirical data such as graphs and/or tables to support the conclusion.

      • Quality of question

        • Is it clear what question is being asked?
        • Is the question non-trivial?
        • Is the question specific to a puzzle (or puzzles)?
        • Would a reader find the answer interesting?

      • Appropriateness of method

        • Is the method aligned with the question: can it give an answer?
        • Are metrics and independent/dependent variables clear?
        • Is the tool or measurement method appropriate for the accuracy/precision needed?

      • Quality of data

        • Is the data clearly presented?
        • Are any important properties of the experimental environment described?
        • Are there sufficient data points to allow conclusions to be drawn?

      • Analysis and insight

        • Is the answer or result of the experiment clearly stated (or equally is the lack of a clear answer identified)?
        • Does the conclusion draw upon the data presented?
        • Does the conclusion show insight beyond simply reporting results?

    • The word limit is to avoid people spending too much time on writing long reports, and also to enforce concision and clarity of communication.

    • This section is deliberately open-ended, and is intended to assess your ability to formulate your own questions and design experiments, rather than just following instructions (this is a masters level course, after all).

    • It is worth thinking of this part as preparation for final year project evaluation sections, as your project evaluation should be addressing all these components too.

Performance metric

Performance is defined in terms of the number of puzzles of increasing scale executed within a fixed time budget. The time budget is fixed at $t_B=60$ seconds for each puzzle, and the budget includes the entirety of Puzzle::Execute.

The sequence of scales is determined according to a schedule for each puzzle, which maps an index $i&gt;=1$ to a sequence of scales $s_1,s_2,s_3,...$. The scale schedule is intended to match the inherent scaling properties of each puzzle, and balances some exploration of smaller scales, while also allowing faster implementations to push up to larger scales. The sequence as given is defined ising a random term $U$ to make it non-deterministic; so it is possible to work out what the sequence looks like, but not the precise numbers (to avoid over-fitting). $U$ is a uniform random number in the range $[0,1)$. For assessment purposes, the sequence of input scales and actual inputs for a given puzzle will be identical across all submissions.

To create a continuous metric, the puzzle which is executing when the timer expires will be added pro-rata based on "how far" it had got through. If we have a sequence of scales $s_1, s_2, s_3, ...$ and an implementation which takes $f(s)$ seconds at scale $s$, then the puzzles in the sequence will complete at $t_j = \sum_{i=1}^{j} f(i)$. The sequence of complete times $t_1,t_2,t_3, ... t_{n},t_{n+1}$, will eventually exceed the time budget $t_B$ at some point $n$, which occurs when $t_{n} &lt;= t_B &lt; t_{n+1}$. We consider $n$ puzzles to be completed, and $(t_B-t_{n})/(t_{n+1}-t_{n})$ of the final puzzle to have been completed, for a final metric of:

n+(t_B-t_{n})/(t_{n+1}-t_{n})

In order to manage execution time in assessment (e.g. in the case of an infinite loop), if $1.5*t_B &lt; t_{n+1}$ then we assume that $t_{n+1} = \infty$. Practically speaking this means that if $t_B=60$ then the timeout for the final puzzle is 90 seconds.

Puzzle Sequence Reference Competent Expert
rank 50+(i*50+U*20)^2 41.8 44.6 60.2
decompose 20+(i*30+U*10)^1.2 15.2 26.8 38.8
ising 20+(i*20+U*5) 14.7 14.7 31.7
integral 20+(i*20+U*5) 15.8 59.0 172.6

Note that in the case of ising our competent person was able to correctly parallelise using TBB in a number of ways and also tried some OpenCL, but did not manage to make it any faster despite using more cores. According to the marks schema that means that if you manage to make ising faster, then you start from a base level of 40%. Note that ising is not specifically a harder problem, but it requires more thought and analysis to determine where to start.

The expert observed that they weren't at the limits of performance on any puzzle, only of implementation time, so if you end up with higher performance don't assume you've done something wrong.

Getting Started

Drop into the root of the repo and do make all. This should produce a number of executables:

  • bin/run_puzzle engine_name scale [logLevel] : General purpose driver, which does the following steps:

    1. Creates an instance of engine_name.
    2. Creates an input for the chosen puzzle type using the given scale.
    3. Executes the engine on the puzzle input and captures the output.
    4. Executes the reference implementation on the same puzzle input and captures the output.
    5. Verifies that the two solutions are the same.

  • bin/create_input puzzle_name scale [logLevel] : Creates an input for the given puzzle and scale, and then writes it (as binary!) to stdout.

  • bin/execute_puzzle engine|"ref" [logLevel] : Reads a problem from stdin, uses the chosen engine to solve it, then writes the solution to stdout. Selecting "ref" as the engine will use the reference solver.

  • bin/compare_puzzle_output inputFile refFile gotFile [logLevel] : Takes in an input problem, a reference solution, and an alternative solution, and checks that the two solutions are the same. The exit code of the program is 0 iff the two solutions match. Not that for some puzzles the answers do not have to be bit-exact equal, so two different outputs may both be correct.

The different programs are intended to make it easy to write infrastructure for testing performance and correctness. For example, if one wished to test an engine called "ising.tbb" at a number of different scales, one could script something along these lines:

#!/bin/bash
ENGINE="ising.tbb"
PUZZLE=${ENGINE%%.*}
SCALES="100 150 200"
WORKING=.tmp
mkdir ${WORKING}
for SCALE in $SCALES ; do
  bin/create_puzzle_input ${PUZZLE} ${SCALE} > ${WORKING}/${PUZZLE}.${SCALE}.input
  cat ${WORKING}/${PUZZLE}.${SCALE}.input | bin/execute_puzzle "ref" > ${WORKING}/${PUZZLE}.${SCALE}.ref
  cat ${WORKING}/${PUZZLE}.${SCALE}.input | bin/execute_puzzle ${ENGINE} > ${WORKING}/${PUZZLE}.${SCALE}.${ENGINE}.got
  bin/compare_puzzle_output ${WORKING}/${PUZZLE}.${SCALE}.input ${WORKING}/${PUZZLE}.${SCALE}.ref ${WORKING}/${PUZZLE}.${SCALE}.${ENGINE}.got
  if [[ $? -ne 0 ]] ; then
    >&2 echo "FAIL"
    exit 1
  fi
done

Submission

The code in github forms your submission, though you must submit your final hash via blackboard for time-keeping and non-repudiation purposes. Pushes to github after the deadline will not be treated as submissions, unless the new hash is also submitted after the deadline. All members of each group must submit the same hash to show agreement.

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