MCC 2009 Presentations Online

The presentations from the 2009 Swedish Workshop on Multicore Computing (MCC 2009) are now online at the program page for the workshop. Let me add some comments on the workshop per se.

This was the first multicore event that I have been to where we did not have a keynote speaker or technical paper from a hardware company. So there was really nothing here directly about how to build multicore chips. Rather, the workshop tended to be about how to program, use, measure performance on, verify software for, and generally work with multicore chips. From the perspective of software people, rather than hardware designers.

Obviously, hardware aspects enter into such talks, but it is the perspective of a user, not a designer. For example, a hardware designer could explain how an atomic compare-and-swap is optimized in a multicore device. But here, we saw measurements on the actual operation latencies observed on real machines using such operations. Quite refreshing, and closer to my personal interests.

The keynote by Andras Vajda of Ericsson was quite interesting. The slides are not online, but the main points that I picked up and that I might not have considered before:

• Software development costs can mean that the cheapest, fastest, most efficient hardware is not necessarily the most economic. Too hard to code for means the software development time and effort removes the advantage. Obvious, but worth reiterating. Software is king.
• The workload on a cellular basestation can sometimes be highly linear and single-threaded. For example, serving a single terminal with a very high bandwidth LTE connection. And suddenly shift to a massively parallel workload as a crowd of a thousand all suddenly appear and start doing data downloads. And then go back to serial again. This means that the age-old argument that signal processing naturally “conveniently concurrent” (and here) is not always true. Nice point!
• Thus, we need adaptable architectures that can trade serial and parallel performance over time, and rebalance quite quickly. In the same chip.
• He is a firm believer that homogeneous systems will win out in the end, I still hold on to a belief in accelerators and offload engines and DSPs. This is partially because of an admitted focus on servers and services processors, and not on the baseband and signalling side. Makes sense.
• Domain-specific languages (DSL) are the future of efficient programming. Agree.

On the topic of DSLs, there was a question about the cost to support them. To me, that is a non-issue. In the organizations that I have worked, it seems that maintaining a useful DSL requires at most one engineer. Developing one, a few good computer scientists for a fairly limited time. In any case, they tend to appear organically when good programmers generalize repeated tasks.

I gave a keynote about how multicore has impacted virtual platforms (in particular, Virtutech Simics) with the following main points:

• Multicore targets increase the performance pressure on a virtual platform, as more processors will have to be simulated.
• Multicore hosts means that sequential performance of the host is going down compared to the aggregate parallel performance demands from the targets.
• To handle large target systems, the virtual platform itself has to run multithreaded on a multicore host. Getting this in place is a major, interesting, and sometimes painful process.
• Once you have a parallel virtual platform, multicore hosts provide a very nice boost in scalability and the manageable system sizes. A single multithreaded virtual platform process is also a bit easier to manage from a user perspective.
• All features in the virtual platform have to be multicore and multimachine-aware… meaning that they often get a bit harder to use initially, as there is no “default processor” you can fall back to for debugging setups etc. Everything has to be explicitly targeted.
• Multicore targets have proven to  be a great sales driver for virtual platforms, as debugging software on a physical multicore, multichip, multiboard system is just too painful.

Overall, this was a fun event, looking forward to next year at Chalmers!