Bachelor's thesis presentation. Maximilian is advised by Santiago Narvaez Rivas.
SCCS Kolloquium
The SCCS Colloquium is a forum giving students, guests, and members of the chair the opportunity to present their research insights, results, and challenges. Do you need ideas for your thesis topic? Do you want to meet your potential supervisor? Do you want to discuss your research with a diverse group of researchers, rehearse your conference talk, or simply cheer for your colleagues? Then this is the right place for you (and you are also welcome to bring your friends along).
Upcoming talks
Maximilian Dornheim: Implementing rank relabeling in the reshuffle library
SCCS Colloquium |
High-performance computing (HPC) increasingly faces a widening gap between raw floating-point throughput and the effective cost of data movement. As large-scale applications are executed on distributed-memory systems, communication rather than computation frequently becomes the dominant bottleneck. One promising mitigation strategy is rank relabeling (also referred to as rank reordering), i.e. the systematic reassignment of MPI rank identifiers such that communication-heavy pairs of processes are placed “closer” in the logical communicator. By increasing the share of data that can be handled locally (self-communication) and reducing expensive inter-rank traffic, an application can improve overall throughput without changing its numerical kernels.
This thesis investigates the design, implementation, and evaluation of rank relabeling in the reshuffle library, an MPI-based data redistribution framework inspired by COSTA. First, we formulate the relabeling problem as an assignment problem on a communication weight matrix that quantifies how much data each pair of ranks is expected to exchange. We then present two solution strategies: (i) an optimal baseline using the Hungarian algorithm, and (ii) a lightweight deterministic greedy heuristic.The Hungarian method guarantees a globally optimal assignment but exhibits cubic time complexity, whereas the greedy strategy runs in effectively quadratic time and produces near-optimal permutations at significantly lower cost Second, we integrate these strategies into reshuffle by constructing an optimized MPI communicator whose rank numbering reflects the chosen permutation. This integration is exposed through a high-level interface that allows applications to obtain a reordered communicator transparently.
Finally, we evaluate both the cost of computing the relabeling and its impact on overall performance. On communication matrices of increasing size, the greedy heuristic outperforms the Hungarian algorithm by up to one to two orders of magnitude in runtime while preserving useful structure in the resulting mappings. In application-level benchmarks on an 8-rank testbed, rank relabeling improves the runtime of highly unbalanced (skewed) data redistribution patterns by up to 12.4% compared to the default communicator, while offering limited benefit for already well-structured communication patterns. These results demonstrate that topology-aware rank relabeling is both practical and performance-relevant, and they motivate future work on extending the cost model to incorporate hardware topology and node locality.
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Contribute a talk
To register and schedule a talk, you should fill the form Colloquium Registration at least four weeks before the earliest preferred date, at the end of a semester typically even earlier reservation is necessary due to a very high influx of presentations. Keep in mind that we only have limited slots, so please plan your presentation early! In special cases, contact colloquium(at)mailsccs.in.tum.de.
Colloquium sessions are now on-campus. We have booked room MI 02.07.023 for SS25 and MI 00.13.054 for WS25/26. You can either bring your own laptop or send us the slides as a PDF ahead of time. The projector only has an HDMI connection, so please bring your own adapters if necessary.
We invite students doing their Bachelor's or Master's thesis, as well as IDP, Guided Research, or similar projects at SCCS to give one 20min presentation to discuss their results and potential future work. The time for this is typically after submitting your final text. Check also with your study program regarding any requirements for a final presentation of your project work.
New: In regular times, we will now have slots for presenting early stage projects (talk time 2-10min). This is an optional opportunity for getting additional feedback early and there is no strict timeline.
Apart from students, we also welcome doctoral candidates and guests to present their projects.
During the colloquium, things usually go as follows:
- 10min before the colloquium starts, the speakers setup their equipment with the help of the moderator. The moderator currently is Ana Cukarska. Make sure to be using an easily identifiable name in the online session's waiting room.
- The colloquium starts with an introduction to the agenda and the moderator asks the speaker's advisor/host to put the talk into context.
- Your talk starts. The scheduled time for your talk is normally 20min with additional 5-10min for discussion.
- During the discussion session, the audience can ask questions, which are meant for clarification or for putting the talk into context. The audience can also ask questions in the chat.
- Congratulations! Your talk is over and it's now time to celebrate! Have you already tried the parabolic slides that bring you from the third floor to the Magistrale?
Do you remember a talk that made you feel very happy for attending? Do you also remember a talk that confused you? What made these two experiences different?
Here are a few things to check if you want to improve your presentation:
- What is the main idea that you want people to remember after your presentation? Do you make it crystal-clear? How quickly are you arriving to it?
- Which aspects of your work can you cover in the given time frame, with a reasonable pace and good depth?
- What can you leave out (but maybe have as back-up slides) to not confuse or overwhelm the audience?
- How are you investing the crucial first two minutes of your presentation?
- How much content do you have on your slides? Is all of it important? Will the audience know which part of a slide to look at? Will somebody from the last row be able to read the content? Will somebody with limited experience in your field have time to understand what is going on?
- Are the figures clear? Are you explaining the axes or any other features clearly?
In any case, make sure to start preparing your talk early enough so that you can potentially discuss it, rehearse it, and improve it.
Here are a few good videos to find out more:
- Simon Peyton Jones: How to Give a Great Research Talk (see also How to Write a Great Research Paper)
- Susan McConnell: Designing effective scientific presentations
- Jens Weller: Presenting Code
Did you know that the TUM English Writing Center can also help you with writing good slides?
Work with us!
Do your thesis/student project in Informatics / Mathematics / Physics: Student Projects at the SCCS.