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Supercomputers: Obama orders world's fastest computer

bbc.co.uk

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Re: Supercomputers: Obama orders world's fastest computer

#71

Post by Trombone12 »

dekhn wrote: post #41
ssully wrote: post #32

Earlier quoted context omitted.

Argonne National Labs, which is 5th fastest I think, is used for weather models, material science, and more[1] [1] http://www.alcf.anl.gov/

There are dual-use systems which run classified and non-classified codes (they can be partitioned.. They typically live at LANL or LLNL rather than ANL or Berkeley (Berkeley in particlar doesn't do any classified work). Note that most classified codes are actually physics/material/explosion/plasma physics simulations and you can't always tell they are running on your system. I checked the list of projects running on…

Nucleosynthesis of heavier materials in supernova explosions and neutron star mergers are two cases of problems that I guess are used for "publicly" validating dark codes.

(I know a guy that Los Alamos is trying to recruit to do some dark work for them, and he does nucleosynthesis in neutron star mergers.)

Re: Supercomputers: Obama orders world's fastest computer

#72

Post by dekhn »

Trombone12 wrote: post #71
dekhn wrote: post #41

Earlier quoted context omitted.

There are dual-use systems which run classified and non-classified codes (they can be partitioned.. They typically live at LANL or LLNL rather than ANL or Berkeley (Berkeley in particlar doesn't do any classified work). Note that most classified codes are actually physics/material/explosion/plasma physics simulations and you can't always tell they are running on your system. I checked the list of projects running on…

Nucleosynthesis of heavier materials in supernova explosions and neutron star mergers are two cases of problems that I guess are used for "publicly" validating dark codes. (I know a guy that Los Alamos is trying to recruit to do some dark work for them, and he does nucleosynthesis in neutron star mergers.)

Those would be useful, but typically the validation codes use terms like "multiscale combustion physics" or "coupled neutron/radiation transport".

I think the folks simulating supernova and neutron stars have a lot of physics overlaps, but I don't think that data is used directly for stockpile stewardship.

Re: Supercomputers: Obama orders world's fastest computer

#73

Post by vmarsy »

davegardner wrote: post #14

10 years ago the fastest supercomputer was BlueGene/L which was rated at 136.8 TFlop/s. The current fastest supercomputer is rated at 33,862.7 TFlop/s, or 247 times faster. It seems to me that the aim of taking 10 years to build a supercomputer that is only 20 times faster than the current one might fall a little short if it's aiming to take the top spot.

This isn't only about the FLOPS, the big trend of these countries* ordering new supercomputers by 2020/2025 is very focused on power. Current supercomputers consume a lot.

Also the FLOPS measurement is a bit broken: It focuses on dense linear algebra problem, for which GPU or other accelerators boost the results easily. If all you plan to do is running simulations that are easily parallelized on GPU it is fine, for other types of programs it is hard to tell which is the fastest supercomputer.

* France is also ordering a would -be top 10 supercomputer : http://www.hpcwire.com/off-the-wire/the-cea-agency-and-atos-...

Re: Supercomputers: Obama orders world's fastest computer

#74

Post by nerdcity »

davegardner wrote: post #14

10 years ago the fastest supercomputer was BlueGene/L which was rated at 136.8 TFlop/s. The current fastest supercomputer is rated at 33,862.7 TFlop/s, or 247 times faster. It seems to me that the aim of taking 10 years to build a supercomputer that is only 20 times faster than the current one might fall a little short if it's aiming to take the top spot.

Then they just can just "order" another one. We're talking government here. Declaring faster computers by government fiat is already a dumb idea.

Re: Supercomputers: Obama orders world's fastest computer

#75

Post by sevensor »

dekhn wrote: post #45

It looks like they are explicitly saying they want to make a machine that works for both types of HPC -- classic low-latency high-bandwidth internode communication (physics simulations) and modern Internet-driver high-bandwidth storage/node communications. This is because the supercomputer community has long ignored the Internet-style of computation (MapReduce etc). But most of the new generation of scientists are ad…

> especially when the community has little or no skill at building NG Internet HPC systems

I would argue that the community of people who actually have the skills to take advantage of the interconnects in a classic HPC system is vanishingly small, and in consequence we've overbuilt them on an epic scale.

Allow me to vent. I had the good fortune to have a login on a "petascale" HPC system, and access to an allocation of hours.

The /scratch filesystem would fail weekly, which killed everybody's jobs. If you had a big run going when /scratch failed, you lost everything. Scratch failed so much because the models that were being used often did wildly inappropriate amounts of file IO --- debugging print statements, detailed intermediate calculations, excessively verbose output --- that worked all right in development but when run in parallel brought the filesystem to its knees.

Furthermore, the login nodes were almost unusably slow because of all the Python and Perl post-processing scripts running on them. This isn't even a matter of users being cheap with their hours --- post-processing would have been a tiny fraction of their allocations. Instead, it's that many of them gave no thought at all to how the post-processing might be structured and run through the batch scheduler, and saw no downside to abusing the login nodes for that purpose.

In conclusion, I can attest to at least one HPC system that was badly mismatched to its users' needs and level of sophistication, despite allocations of hours being awarded only to a small number of researchers from across the country through a highly competitive process. Building these things serves national and institutional pride far more than any utilitarian interest.

Re: Supercomputers: Obama orders world's fastest computer

#77

Post by dekhn »

sevensor wrote: post #75
dekhn wrote: post #45

It looks like they are explicitly saying they want to make a machine that works for both types of HPC -- classic low-latency high-bandwidth internode communication (physics simulations) and modern Internet-driver high-bandwidth storage/node communications. This is because the supercomputer community has long ignored the Internet-style of computation (MapReduce etc). But most of the new generation of scientists are ad…

> especially when the community has little or no skill at building NG Internet HPC systems I would argue that the community of people who actually have the skills to take advantage of the interconnects in a classic HPC system is vanishingly small, and in consequence we've overbuilt them on an epic scale. Allow me to vent. I had the good fortune to have a login on a "petascale" HPC system, and access to an allocation…

You're describing an exceptionally poorly built and used system. That said, it's not inconsistent with what I've seen as well.

My claim is that the design of classic interconnects is a big waste of money, because only a few codes need it, yet the cost dominates (>50%) of the cluster. I've learned, from years of studying Google's papers, that there are better ways to build code that communicates, and those mechanisms are much easier to teach to scientists and computer scientists than MPI.

Re: Supercomputers: Obama orders world's fastest computer

#78

Post by lorenzhs »

dekhn wrote: post #45

It looks like they are explicitly saying they want to make a machine that works for both types of HPC -- classic low-latency high-bandwidth internode communication (physics simulations) and modern Internet-driver high-bandwidth storage/node communications. This is because the supercomputer community has long ignored the Internet-style of computation (MapReduce etc). But most of the new generation of scientists are ad…

One of the largest challenges in building an exascale cluster is communication. Computing power increases at a higher rate than memory throughput does, and memory throughput increases faster than communication infrastructure advances.

Many argue that an exascale computer can only be cost efficient if the communication capabilities scale highly sublinearly with the computation done in the subsystems [1]. In particular, you can't move the data, and new algorithms are needed that can deal with data that is arbitrarily distributed. This is quite challenging and unfortunately the theoretical computer science community seems to have decided that distributed memory algorithms have been covered since the 90s and are not worth their time. Yet they ignore the progress that has been made in other models of computation since, and many algorithmic improvements of the last decades are not applicable. It is high time to develop communication-efficient algorithms for the basic "toolbox".

I guess what I'm trying to say is that you can't just throw MapReduce at an Exascale machine and expect it to perform well. Instead, you need an environment that is rich in primitives that have been implemented in a communication-efficient way. It's faster and cheaper to spend a little more effort on local communication if that allows for reduced communication volume (and/or the number of connections that need to be established!).

The issue I have with the MapReduce approach is that it doesn't particularly care about data locality. Thus it is very hard to achieve communication volume sublinear in the input size, which is absolutely deadly in an exascale setting.

I also understand the frustration with MPI, it is a very low-level API focused on data movement. It can be rather frustrating to use, but there do exist tools to make it more fun (Boost.MPI with C++11/14 is an excellent example). That said, with a well-engineered set of algorithmic tools, ideally you wouldn't need to use low-level MPI calls at all. However, MPI still remains a useful tool to implement these things.

Exascale computing requires us to rethink a lot of things.

[1] http://www.ipdps.org/ipdps2013/SBorkar_IPDPS_May_2013.pdf Shekhar Borkar (Intel), Keynote presentation at the 2013 IEEE International Parallel & Distributed Processing Symposium

Re: Supercomputers: Obama orders world's fastest computer

#79

Post by unfamiliar »

bjacobel wrote: post #15

> The supercomputer would be 20 times quicker than the current leading machine, which is in China. So given Moore's Law, by the time it's finished in 2025, it will be 50 times slower than 2025's fastest? Yes, yes, Moore's Law is slowing, transistors on a chip =/= flops, etc. Still seems like they'd want to aim higher than 20x in 10 years.

You're assuming the goal is to build the fastest supercomputer in the world. I think the goal is probably closer to "get the computing resources we need at the lowest cost".

Re: Supercomputers: Obama orders world's fastest computer

#80

Post by apawloski »

jakub_h wrote: post #63
dekhn wrote: post #36

Earlier quoted context omitted.

This is not remotely true for a wide range of codes that matter to the supercomputing industry.

And by "codes", you mean specific legacy software artifacts written in FORTRAN (note that I'm not even spelling it as Fortran)? Of course that's a problem.

Write in any language you want; that's irrelevant to the nature of the computations being done here.

By codes they mean -- at the minimum -- pretty much anything that requires frequent communication between any or all nodes as a necessary part of computation. (For example, simulations across a large 3D space, where the changing states of particles on node A directly impacts the states of particles on adjacent nodes.)

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