Supercomputers: Obama orders world's fastest computer • Hacker News Board

Re: Supercomputers: Obama orders world's fastest computer

#81

Post by mbell » Thu, Jul 30, 2015, 3:54 PM UTC

rayiner wrote: post #48

angdis wrote: post #20

I suppose that "supercomputers" are all multi-processor these days, so the colossal FLOP numbers are counted as an aggregation over many processors and one has to coordinate these processors in any application that takes advantage of the FLOP specs. Now I am curious what is the fastest single processor?

On a per-core basis, probably Power 8: http://www.anandtech.com/show/9193/the-xeon-e78800-v3-review...

I guess it depends on how 'core' is defined. A single core of an Intel CPU can work on 2 threads at a time, the power 8 can work on 8.

I assume that when most people think of 'single core' performance, they really mean 'single thread'. I think Intel's CPUs win out there, based on your linked benchmarks.

Re: Supercomputers: Obama orders world's fastest computer

#82

Post by juliangregorian » Thu, Jul 30, 2015, 3:57 PM UTC

jerven wrote: post #33

azaras wrote: post #11

Earlier quoted context omitted.

What does it simulate? Thanks.

That should be Piz Daint at CSCS, so Super conductor behavior, weather and many other things. Mostly non embarrassingly parallel problems, where its high speed interconnect pays off.

Can we please stop calling things "embarrassingly parallel". Just what the hell is embarrassing about highly parallelizable algorithms?

Re: Supercomputers: Obama orders world's fastest computer

#83

Post by [deleted] » Thu, Jul 30, 2015, 3:57 PM UTC

apawloski wrote: post #12

simi_ wrote: post #8

IMHO if you need to break down a task well enough to run on a supercomputer, there isn't a lot more to do to make it run on a regular server farm. edit: Actually, in the scenarios you'd use a supercomputer for, the added latency and overhead (shoddy servers, network, etc.) would most likely make the run time orders of magnitude higher.

Maybe for embarrassingly parallel tasks, but if you require nontrivial interprocess communication, a server farm can't compete with the interconnect of a modern supercomputer.

[deleted]

Re: Supercomputers: Obama orders world's fastest computer

#84

Post by [deleted] » Thu, Jul 30, 2015, 3:58 PM UTC

TallGuyShort wrote: post #70

edpichler wrote: post #35

Earlier quoted context omitted.

I think this do not advanced more just because of economic reasons. I have have read last 10 years that Processing is a lot more cheaper did by network of computers and clusters, instead of a expensive supercomputer that also demands an appropriate building and infrastructure.

Modern supercomputers are essentially clusters, but with much more advanced network topologies and technologies, shared storage, etc. It's not just one monolothic machine. However, the types of computation performed by the top supercomputers are rarely the "embarassingly parallel" programs you can easily distribute via an @Home-style program, or something like Hadoop. They do depend heavily on very reliable, very low…

[deleted]

Re: Supercomputers: Obama orders world's fastest computer

#85

Post by ska » Thu, Jul 30, 2015, 4:02 PM UTC

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.

No, that means specific problem domains that are not easily partitioned, and where latency or affinity are the primary performance constraints.

There are still some fortran libraries in large scale use for this sort of thing. They are still in use because they are very good, and replacing them would be very expensive for little gain.

Re: Supercomputers: Obama orders world's fastest computer

#86

Post by lorenzhs » Thu, Jul 30, 2015, 4:03 PM UTC

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…

I would argue that many of the failures you describe are due to a lack of libraries that can exploit these systems. You can't expect every biologist to be an expert in distributed computing. The HPC and algorithms communities failed to consider the users of these systems and happily tinkered in their academic niches. All the while, what was actually needed were easy to use libraries that allowed non-experts to benefit from the advances made. (Also, the algorithms community has lost interest in distributed memory computing).

The abuse of /scratch and the login nodes sounds like a classical mixture of not knowing, not caring, and limited time. That isn't something that has a technical solution.

Re: Supercomputers: Obama orders world's fastest computer

#87

Post by rwallace » Thu, Jul 30, 2015, 4:08 PM UTC

dekhn wrote: post #77

sevensor wrote: post #75

Earlier quoted context omitted.

> 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…

That's true for many purposes, but is it true for physical simulations? Don't they need communication on every time step?

Re: Supercomputers: Obama orders world's fastest computer

#88

Post by lorenzhs » Thu, Jul 30, 2015, 4:09 PM UTC

juliangregorian wrote: post #82

jerven wrote: post #33

Earlier quoted context omitted.

That should be Piz Daint at CSCS, so Super conductor behavior, weather and many other things. Mostly non embarrassingly parallel problems, where its high speed interconnect pays off.

Can we please stop calling things "embarrassingly parallel". Just what the hell is embarrassing about highly parallelizable algorithms?

The term "embarrassingly parallel" doesn't refer to algorithms, it refers to problems which can be computed in such a manner, stating that they're not very interesting for parallel algorithms research. But yeah, it's kind of a stupid term. Would you be okay with "pleasingly parallel"? ;)

Re: Supercomputers: Obama orders world's fastest computer

#89

Post by semi-extrinsic » Thu, Jul 30, 2015, 4:10 PM UTC

bbgm wrote: post #19

bjacobel wrote: post #16

Earlier quoted context omitted.

It could very well be that there's diminishing returns involved but I agree - they should be aiming to surpass the current tech by at last 100x in the next ten years.

The current trend [1] would suggest that exascale is not on that kind of trajectory. The dominance of non US countries (especially China) in the Top500 rankings is as much a driver here. 1. http://www.theplatform.net/2015/07/13/top-500-supercomputer-...

1. The top 500 list is broken, as people who are serious about real world applications give essentially zero shits about Linpack.

2. The dominance of China is achieved through the use of Xeon Phi accelerators, which may be great for Linpack, but have not made much of a splash for applications yet. GPUs are solidly beating Intel's accelerator offering both on adaptation and performance.

Re: Supercomputers: Obama orders world's fastest computer

#90

Post by dekhn » Thu, Jul 30, 2015, 4:13 PM UTC

rwallace wrote: post #87

dekhn wrote: post #77

Earlier quoted context omitted.

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…

That's true for many purposes, but is it true for physical simulations? Don't they need communication on every time step?

I would say no.

Here is my argument: when I worked for DOE, everybody told me I had to run my MD simulations on a super computer using all the processors, and I would judged on my parallel efficiency. This meant using a code that used MPI to communicate at every (or every N) timesteps. I asked, instead, "Why not just run N independent simulations, and pool the results?" In this case, you run an M-thread simulation on each machine (where M = number of cores on the machine) with no internode communication at all except to read input files and write output files.

The short answer is, that approach works just fine, but the DOE supercomputer people won't let you run embarassingly parallel codes because they already spent money on the interconnect to run tightly coupled codes.

In reponse to this, I went to Google, built Exacycle (loosely coupled HPC) and published this well-cited paper: http://www.ncbi.nlm.nih.gov/pubmed/24345941 which in my opinion put the last nail in the coffin of DOE-style physics simulations for molecular dynamics.

That said, there are systems which are so large you can't practically simulate a single instance of the system on a single machine, so you have to partition. Simulating the ribosome is a nice example. However, simulating the ribosome currently provides no valuable scientific data except to tell us that we have major problems with our simulation systems (force field errors, missing QM, electrostatic approximations,e tc).