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

Re: Supercomputers: Obama orders world's fastest computer

#101

Post by jedbrown » Thu, Jul 30, 2015, 5:11 PM UTC

ajdecon wrote: post #98

amelius wrote: post #93

Earlier quoted context omitted.

> Also the FLOPS measurement is a bit broken Does anybody have a better measurement? Perhaps it could be the size of the matrix that can be inverted on it in an hour of time, with IEEE double precision floats, using some standard algorithm.

The "High Performance Conjugate Gradients" benchmark was proposed a couple years ago as an alternative metric for ranking supercomputers. Its proponents claim its behavior is more similar to real applications (irregular access patterns, lower ratio of computation to memory access, etc), compared to linear algebra problems like the "High Performance Linpack" benchmark currently used by the Top500. The different perfor…

HPCG basically measures STREAM and has many technical flaws making it scale-dependent and difficulty to adjudicate. As codeveloper of a different benchmark, I'll just cite this paper from a third party. https://hpgmg.org/static/MarjanovicGraciaGlass-PerformanceMo...

The reality is that there are many dimensions to supercomputing performance and it's impossible for one number to capture the utility of the machine. Our HPGMG benchmark (https://hpgmg.org) attempts to strike a balance and give useful supplementary information. I do think it's better than any other single benchmark for evaluating today's machines and will also prove to be more durable over time.

Re: Supercomputers: Obama orders world's fastest computer

#102

Post by ajdecon » Thu, Jul 30, 2015, 5:15 PM UTC

jedbrown wrote: post #101

ajdecon wrote: post #98

Earlier quoted context omitted.

The "High Performance Conjugate Gradients" benchmark was proposed a couple years ago as an alternative metric for ranking supercomputers. Its proponents claim its behavior is more similar to real applications (irregular access patterns, lower ratio of computation to memory access, etc), compared to linear algebra problems like the "High Performance Linpack" benchmark currently used by the Top500. The different perfor…

HPCG basically measures STREAM and has many technical flaws making it scale-dependent and difficulty to adjudicate. As codeveloper of a different benchmark, I'll just cite this paper from a third party. https://hpgmg.org/static/MarjanovicGraciaGlass-PerformanceMo... The reality is that there are many dimensions to supercomputing performance and it's impossible for one number to capture the utility of the machine. Our…

Interesting! I'll have to check this out, thanks!

Re: Supercomputers: Obama orders world's fastest computer

#103

Post by apawloski » Thu, Jul 30, 2015, 5:17 PM UTC

dekhn wrote: post #94

apawloski wrote: post #80

Earlier quoted context omitted.

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.)

You can't write your code in any language you want on a supercomputer. Also, there is a wide range of literature about communication patterns for supercomputer apps; my argument is that often times, to solve the problem that matters, you may not actually need to run the simulation you think you do. It's more that people are just used to running that way. For example, with MD, you can run 1 sim parallelized over 100 m…

I'm somewhat confused -- I thought we were arguing similar points?

I don't want to drag this out, but where do you see the language constraint? You need an MPI binding, sure, but what else?

Re: Supercomputers: Obama orders world's fastest computer

#104

Post by _delirium » Thu, Jul 30, 2015, 5:22 PM UTC

mathetic wrote: post #95

unfamiliar wrote: post #79

Earlier quoted context omitted.

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".

Well, the title literally says "world's fastest computer."

Probably fluff added by the headline writer to sound more exciting. The White House press release doesn't make world's-fastest claims: https://www.whitehouse.gov/blog/2015/07/29/advancing-us-lead...

Re: Supercomputers: Obama orders world's fastest computer

#105

Post by dekhn » Thu, Jul 30, 2015, 5:27 PM UTC

apawloski wrote: post #103

dekhn wrote: post #94

Earlier quoted context omitted.

You can't write your code in any language you want on a supercomputer. Also, there is a wide range of literature about communication patterns for supercomputer apps; my argument is that often times, to solve the problem that matters, you may not actually need to run the simulation you think you do. It's more that people are just used to running that way. For example, with MD, you can run 1 sim parallelized over 100 m…

I'm somewhat confused -- I thought we were arguing similar points? I don't want to drag this out, but where do you see the language constraint? You need an MPI binding, sure, but what else?

No, the people who run the clusters won't let you run any language just because it has an MPI binding. They invest a lot in ensuring peak performance, and right now, only C++ and FORTRAN can achieve that. Very few, if any, major supercomputer centers support Java codes.

Re: Supercomputers: Obama orders world's fastest computer

#106

Post by ypcx » Thu, Jul 30, 2015, 5:29 PM UTC

phreeza wrote: post #27

A bit more informative is the actual fact sheet put out by the white house [1]. What they are really aiming for is exa scale computing, which they define as being capable of applying exaFlops to exabytes. From my limited knowledge, the latter will actually be the bigger deal. As pointed out elsewhere, an exaflop supercomputer will probably come around beforehand. [1] https://www.whitehouse.gov/sites/default/files/mic…

Clearly designed to run AI for cyber-warfare / cyber-defense purposes? William Gibson's Black Ice coming to life?

Re: Supercomputers: Obama orders world's fastest computer

#107

Post by apawloski » Thu, Jul 30, 2015, 5:38 PM UTC

dekhn wrote: post #105

apawloski wrote: post #103

Earlier quoted context omitted.

I'm somewhat confused -- I thought we were arguing similar points? I don't want to drag this out, but where do you see the language constraint? You need an MPI binding, sure, but what else?

No, the people who run the clusters won't let you run any language just because it has an MPI binding. They invest a lot in ensuring peak performance, and right now, only C++ and FORTRAN can achieve that. Very few, if any, major supercomputer centers support Java codes.

Oh, you're talking about a policy limitation, not a technological one. (And if you're talking about the DOE or NSF/Teragrid/XSEDE clusters, then you're probably right. Haven't touched those in years -- and even when I did, I wasn't doing anything crazy.)

Re: Supercomputers: Obama orders world's fastest computer

#108

Post by juliangregorian » Thu, Jul 30, 2015, 5:38 PM UTC

lorenzhs wrote: post #88

juliangregorian wrote: post #82

Earlier quoted context omitted.

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"? ;)

Potato, potato. I don't make the rules. I just think "embarrassingly parallel" sounds like a college freshman trying way too hard to sound smart and cool.

Re: Supercomputers: Obama orders world's fastest computer

#109

Post by bhouston » Thu, Jul 30, 2015, 5:43 PM UTC

ajdecon wrote: post #98

amelius wrote: post #93

Earlier quoted context omitted.

> Also the FLOPS measurement is a bit broken Does anybody have a better measurement? Perhaps it could be the size of the matrix that can be inverted on it in an hour of time, with IEEE double precision floats, using some standard algorithm.

The "High Performance Conjugate Gradients" benchmark was proposed a couple years ago as an alternative metric for ranking supercomputers. Its proponents claim its behavior is more similar to real applications (irregular access patterns, lower ratio of computation to memory access, etc), compared to linear algebra problems like the "High Performance Linpack" benchmark currently used by the Top500. The different perfor…

It isn't that different, 7 of the top 10 of the top500 are in the top 10 of this HPCG benchmark. Most barely changed positions.

Re: Supercomputers: Obama orders world's fastest computer

#110

Post by ddingus » Thu, Jul 30, 2015, 5:51 PM UTC

marvelous wrote: post #29

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?

I don't think knowing that is usefull. "Single processors" are all superscalar or pipelined these days, so the colossal single-thread FLOP numbers are counted as an aggregation over many arithmetic units and one has to coordinate these units (mainly avoiding branch mispredictions) in any application that takes advantage of them.

It's still relevant. Some applications remain single threaded due to data dependencies.

Mechanical CAD geometry kernels are one such application. Recently, I had a use case that demanded the peak single threaded performance.

In PC land, it's this chip clocked at 4.x Ghz: Intel® Core™ i7-4790K. It's multi-core performance is pretty great too, so it's not that big of a trade-off to maximize single thread performance.

I would be very interested in knowing what faster solutions exist. Are there any, regardless of instruction set?