/hpce-2017-cw5

Primary LanguageC++

HPCE 2017 CW5

  • Issued: Fri 10th Nov
  • Due: Fri 24th Nov, 22:00

Errata

  • 2017/11/14 18:56 : Particularly dumb mistake in heat_world. I notice quite a lot of groups already fixed in their repo based on past experience, so while it is a breaking change it's fine to fix. this commit. Thanks to @thomasrarris.

  • 2017/11/12 19:57 : Fix to calculation of p due to a missing .0. This is a breaking change - this commit shows the exact change. Thanks to @Wiijah.

  • 2017/11/12 09:31 : 2nd update to Gaussian Blur due to a conversion error. This is a breaking change - this commit shows the exact change. Thanks to @malharjajoo.

  • 2017/11/11 15:27 : Update to Gaussian Blur due to typo. This is a breaking change - this commit shows the exact change. Thanks to @pufik1337 for noticing it.

Specification

You have been given the included code with the goal of making things faster. For our purposes, faster means the wall-clock execution time of puzzler::Puzzle::Execute, across a broad spectrum of scale factors. There is also an emphasis on good scaling - how large a scale parameter can be executed?

The set of driver programs included are fairly basic, and have no particular importance beyond making it easy to call Execute (testing will use a different driver program). You can infer how they work from the source; look at the serenity_now makefile targe; or there is some brief guidance here.

The target platform is an AWS GPU (g2.2xlarge) instance. I would prefer to use a bigger instance, but this is the most economical, and I don't want people running out of money here. I will probably do some short runs on the submitted versions with a bigger instance (e.g. a p3.16xlarge, at $27 an hour...), just out of interest, but they will not be assessed.

The target AMI will be the public HPCE-2017-GPU-Image AMI. The AMI has OpenCL GPU and software providers installed, alongside TBB. You can determine the location of headers and libraries by starting up the AMI.

People working in triples must provide a solution to all six puzzles.

People working in pairs must choose four. The chosen puzzles will be indicated in the documentation.md file, and the choice must be made by the pair. If a pair has not made a clear choice of four for the final submision, then four will be picked at random.

Triples have the advantage of knowing they need to do all puzzles, so there is no paralysis of choice, but they have to do everything. Pairs have the opportunity to attack more than four and try to pick the best performing or "easiest", but may then not be able to probe as deeply. To the best of my estimation there is no inherent advantage one way or the other - the only thing that matters is the ability of the people in the team, and not the choice of 2 or 3.

Meta-specification

You've now got some experience in different methods for acceleration, and a decent working knowledge about how to transform code in reasonable reliable ways. This coursework represents a fairly common situation - you haven't got much time, either to analyse the problem or to do very low-level optimisation, and the problem is actually a large number of sub-problems. So the goal here is to identify and capture as much of the low-hanging performance fruit as possible while not breaking anything. If time allows you can dig deeper, but you first want to be focussing on easy initial wins, and looking for any clear asumptotic improvements (if they exist).

The code-base I've given you is somewhat baroque, and despite having some rather iffy OOP practises, actually has things quite reasonably isolated. You will probably encounter the problem that sometimes the reference solution starts to take a very long time at large scales, but the persistence framework gives you a way of dealing with that.

Beyond that, there isn't a lot more guidance, either in terms of what you should focus on, or how exactly it will be measured. Part of the assesment is in seeing whether you can work out what can be accelerated (using parallelisation, restructuring, and optimisation), and also seeing if you can focus your efforts on the write parts.

The allocation of marks I'm using is:

  • Compilation/Execution: 10%

    • How much work do I have to do to get it to compile and run. Everyone should get all marks here.

  • Performance: 70%

    • You are competing with each other here, so there is an element of judgement in terms of how much you think others are doing or are capable of.

    • Marks for any puzzle which gives incorrect outputs will be reduced in proportion to the number of correct outputs. If a puzzle gives correct output only for a proportion p of the inputs tested, the performance mark will be scaled by p^2. You really want to be functionally correct.

    • If a puzzle runs too long and is terminated, it does not count as being incorrect.

    • People working in threes must implement all six puzzles.

    • People working in twos should choose four puzzles, via documentation.md.

    • The performance mark is split equally between the puzzles you chose. So each puzzle is worth 1/6 of the performance marks in a triple, or 1/4 for a pair.

  • Documentation: 20%

    • This should be given by filling in documentation.md, using the format given there. Each section will be evaluated in terms of whether it is coherent, whether it can be understood, and if there is any deeper insight being shown.

    • This section is to encourage concise communication and a bit of reflection, and to reward those who do it well. Some people get fast results through luck, and can't explain why - others get slower results, even though their reasoning and insight was much better.

Deliverable format

  • Anything in the include directory is not owned by you, and subject to change

    • Any changes will happen in an additive way (none are expected for this CW)

    • Bug-fixes to include stuff are still welcome.

  • 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.

  • 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 typing bin/execute_puzzle, and an opencl kernel could be loaded using the relative path provider/something.kernel.

    • Programs which link against and use lib/libpuzzler.a will also link in TBB and OpenCL.

  • 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.

Intermediate Testing

In the second week I'll be occasionally pulling and running tests on all the repositories, and pushing the results back. These tests do not check for correctness, they only check that the implementations build and run correctly (and are also for my own interest in seeing how performance evolves over time) I will push the results into the dt10_runs directory.

If you are interested in seeing comparitive performance results, you can opt in by changing the line count-us-in from no to yes in documentation.md. This will result in graphs with lines for others who also opted in. There is no specific relationship between the median and any assesment metric. The scripts will attempt to run all puzzles, even for those in pairs.

I will pull from the "master" branch, as this reflects good working practise - if there is a testing branch, then that is where the unstable code should be. The master branch should ideally always be compilable and correct, and branches only merged into master once they are stable.

Finally, to re-iterate: the auto tests I am doing do no testing at all for correctness; they don't even look at the output of the tests.

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.