Panic in Multicore Land

MOBE2001 writes "There is widespread disagreement among experts on how best to design and program multicore processors, according to the EE Times. Some, like senior AMD fellow, Chuck Moore, believe that the industry should move to a new model based on a multiplicity of cores optimized for various tasks. Others disagree on the ground that heterogeneous processors would be too hard to program. The only emerging consensus seems to be that multicore computing is facing a major crisis. In a recent EE Times article titled 'Multicore puts screws to parallel-programming models', AMD's Chuck Moore is reported to have said that 'the industry is in a little bit of a panic about how to program multicore processors, especially heterogeneous ones.'"

Comments

Panic?

[jaavaaguru]

I think "panic" is a bit of an over-reaction. I use a multicore CPU. I write software that runs on it. I'm not panicking.

Re:Panic?

[shitzu]

Still, the fact remains that the x86 processors (due to the OS-s that run on them, actually) have not gone much faster in the last 5-7 years. The only thing that has shown serious progress is power consumption and heat dissipation. I mean - the speed the user experiences has not improved much.

Re:Panic?

[leenks]

How is an 80-core cpu a cut down version of a dual-CPU box? This is the kind of technology the authors are discussing, not your Core2 duo MacBook...

Re:Panic?

[Chrisq]

Yes panic is strong, but the issue is not with multi-tasking operating systems assigning processes to different processors for execution. That works very well. The problem is when you have a single CPU-intensive task, and you want to split that over multiple processors. That, in general, is a difficult problem. Various solutions, such as functional programming, threads with spawns and waits, etc. have been proposed, but none are as easy as just using a simple procedural language.

Re:Panic?

[ObsessiveMathsFreak]

That works very well. The problem is when you have a single CPU-intensive task, and you want to split that over multiple processors. That, in general, is a difficult problem.

It is in general, an impossible problem.

Most existing code is imperative. Most programmers write in imperative programming languages. Object orientation does not change this. Imperative code is not suited for multiple CPU implementation. Stapling things together with threads and messaging does not change this.

You could say that we should move to other programming "paradigms". However in my opinion, the reason we use imperative programs so such is because most of the tasks we want accomplished are inherently imperative in nature. Outside of intensive numerical work, most tasks people want done on a computer are done sequentially. The availability of multiple cores is not going to change the need for these tasks to be done in that way.

However, what multiple cores might do is enable previously impractical tasks to be done on modest PCs. Things like NP problems, optimizations, simulations. Of course these things are already being done, but not on the same scale as things like, say, spreadsheets, video/sound/picture editing, gaming, blogging, etc. I'm talking about relatively ordinary people being able to do things that now require supercomputers, experimenting and creating on their own laptops. Multi core programs can be written to make this feasible.

Considering I'm beginning to sound like an evangelist, I'll stop now. Safe money says PCs stay at 8 CPUs or below for the next 15 years.

Re:Panic?

[Saurian_Overlord]

"...the speed the user experiences has not improved much [in the last 5-7 years]."

This may almost be true if you stay on the cutting edge, but not even close for the average user (or the power-user on a budget, like myself). 5 years ago I was running a 1.2 GHz Duron. Today I have a 2.3 GHz Athlon 64 in my notebook (which is a little over a year old, I think), and an Athlon 64 X2 5600+ (that's a dual-core 2.8 GHz, for those who don't know) in my desktop. I'd be lying if I said I didn't notice much difference between the three.

Re:Panic?

[mollymoo]

No matter how easy they make knitting I'm never going to do it, because I don't want to knit my own clothes. I just want ones which look good and work. No matter how easy you make programming most people just aren't going to do it, because they don't want to write their own programs. They just want programs that work.

Re:Panic?

[johannesg]

Let's not be too harsh on ourselves. In most systems today, the bottleneck is the hard disk, not the CPU. No amount of threading will rescue you if your memory has been swapped out.

I write large and complex engineering applications. I have a few threads around, mostly for the purpose of doing calculation and dealing with slow devices. But I'm not going to add in more threads just because there are more cores for me to use. I'll add threads when performance issues requires that I add threads, and not before.

Most software today runs fine as a single thread anyway. The specialized software that requires maximum CPU performance (and is not already bottle-necked by HD or GPU access) will be harder to write, but for everything else the current model is just fine.

If anything, Intel should worry about 99% of all people simply not needing 80 cores to begin with...

Re:Panic?

[TemporalBeing]

"...the speed the user experiences has not improved much [in the last 5-7 years]."

This may almost be true if you stay on the cutting edge, but not even close for the average user (or the power-user on a budget, like myself). 5 years ago I was running a 1.2 GHz Duron. Today I have a 2.3 GHz Athlon 64 in my notebook (which is a little over a year old, I think), and an Athlon 64 X2 5600+ (that's a dual-core 2.8 GHz, for those who don't know) in my desktop. I'd be lying if I said I didn't notice much difference between the three.

Do notice that in 5 years we have barely increased the clock frequency of the CPUs

Do notice that multi-cores don't increase the overall clock frequency, just divide the work up among a set of lower clock frequency cores - yet most programs don't take advantage of that. ;-)

Do notice that despite clock frequencies going from 33 mhz to 2.3 GHz, the user's perceived performance of the computer has either stayed the same (most likely) or diminished over that same time period.

Do notice that programs are more bloated than ever, and programmers are lazier than ever.
...
In the end the GP is right.

Re:Panic?

[Alsee]

spreadsheets, video/sound/picture editing, gaming, blogging

Odd selection of examples. The processing of cells can almost trivially be allocated across 80 cores. Media work can almost trivially be split into chunks across 80 cores. Games usually relatively easy to split, either by splitiing the graphics into chunks or parallelizable physics or other parallelizable simulation aspects.

Oh, and blogging.
My optical mouse has enough processing horsepower inside for blogging.

OPTICAL MOUSE CIRCUITRY:
Has the user pressed a key?
No.
Has the user pressed a key?
No.
Has the user pressed a key?
No.
(repeat 1000 times)
Has the user pressed a key?
No.
Has the user pressed a key?
No.
Has the user pressed a key?
Yes.
OOOO! YES!
QUICK QUICK QUICK! HURRY HURRY HURRY! PROCESS A KEYPRESS! YIPEE!

-

Re:Panic?

[cens0r]

If the 80 core processor can run 10 virtual machines as fast as one machine on the 8 core processor, I would be interested.

Re:Panic?

[TemporalBeing]

What do the OS's that run on them have to do with the processors' performance? Recent processors have had significant improvements in performance in the last 5-7 years, which makes the GP incorrect.

Perhaps you missed my statement about the user's perceived performance. It is true, I grant you, that hardware performance has gotten better. But the user's perception of that performance has not - it's gone the opposite. Some of that is because programmer's rely on a single faster core to correct for their inept programming, lack of optimization, added abstraction layers, etc. However, that is no longer how processors function - they are now two slower processors working together.

And yes, the OS can, and has been able to for years since SMP first came about, spread loads across multiple processors and cores. But that cannot change how a single program functions in and of itself - it cannot make that single program work at any given moment on more than one single core if it was not designed to do so (i.e. if the program is not designed to use multiple threads or processes).

All-in-all, the OP is correct.

The future is here

[downix]

What Mr Moore is saying does have a grain of truth, that generic will be beaten by specific in key functions. The Amiga proved that in 1985, being able to deliver a better graphical solution than workstations costing tens of thousands more. The key now is to figure out which specifics you can use without driving up the cost nor without compromizing the design ideal of a general purpose computer.

Occam and Beyond

[BrendaEM]

Perhaps, panic is a little strong. At the same time, programing languages such as Occam, that are built from the ground up seem very provocative now. Perhaps Occam's syntax could modified to a Python-type syntax for a more popularity.

[Although, personally, I prefer Occam's syntax over that of C's.]

http://en.wikipedia.org/wiki/Occam_programming_language

I think that a tread aware programming language would be good in our multi-core world.

Re:My heterogeneous experience with Cell processor

[TheRaven64]

Well, part of your problem is that you're using a language which is a bunch of horrible syntactic sugar on top of a language designed for programming a PDP-8 on an architecture that looks nothing like a PDP-8.

You're not the only person using heterogeneous cores, however. In fact, the Cell is a minority. Most people have a general purpose core, a parallel stream processing core that they use for graphics and an increasing number have another core for cryptographic functions. If you've ever done any programming for mobile devices, you'll know that they have been using even more heterogeneous cores for a long time because they give better power usage.

No problems for servers

[TheLink]

For servers the real problem is I/O. Disks are slow, network bandwidth is limited (if you solve that then memory bandwidth is limited ;) ).

For most typical workloads most servers don't have enough I/O to keep 80 cores busy.

If there's enough I/O there's no problem keeping all 80 cores busy.

Imagine a slashdotted webserver with a database backend. If you have enough bandwidth and disk I/O, you'll have enough concurrent connections that those 80 cores will be more than busy enough ;).

If you still have spare cores and mem, you can run a few virtual machines.

As for desktops - you could just use Firefox without noscript, after a few days the machine will be using all 80 CPUs and memory just to show flash ads and other junk ;).

Re:My heterogeneous experience with Cell processor

[neomunk]

Heterogeneous cores are already in almost every PC I've seen so far this millennium. Anyone with a GPU is running heterogeneous cores in their machine. How do we handle it? The first half of your second sentence; libraries and frameworks. OpenGL, DirectX and whatnot provide the frameworks we need while the various manufacturers provide the drivers to maintain compatibility with the various APIs. We'll see soon enough (as a result of the Cell) if the same thing (2 or more different libraries for the same processor; one for each of it's core-types) becomes the norm for other heterogeneous core system. I think so, but it may be overlooked by manufacturers who want to view a processor as a unit instead of a compilation of various units. They'll figure it out, these guys aren't MBAs, they're the truly educated. :-D

How to use so many cpu's

[John Sokol]

Back in 2000 I realized that 50 Million transistors of 4004 the first processor ever created, would out perform a P4 with the same transistor count done in the same fab running at the same clock rates. it would be over 10x faster I work out. But how to use such a device?
I had been working with a 100 PC cluster of P4 based systems to do H.264 HDTV compression in realtime. I spread the compression function across the cluster using each system to work on a small part of the problem and flow the data across the CPU's.

Based on this I wanted to build an array of processors on one chip, but I am not a silicon person, just software, driver and some basic electronics. So I looked at various FPGA cores, Arm, MIPS, etc. Then I went to a talk giving by Chuck Moore, author of the language FORTH. He had been building his own CPU's for many years using his own custom tools.

I worked with Chuck Moore for about a year in 2001/2002 on creating a massive multi core processor based on Chucks stack processor.

The Idea was instead of having 1,2 or 4 large processor to have 49 (7 * 7) small light but fast processors in one chip. This would be for tacking a different set of problems then your classic cpus'. It wouldn't be for running and OS or word processing, but for Multimedia, and cryptography, and other mathematic problems.

The idea was to flow data across the array of processors.
Each processor would run at 6Ghz, with 64K word of Ram each.
21 Bit wide words and bus (based off of F21 processor)
this allows for 4x 5bit instructions on a stack processor that only has 32 instructions.
Since it's a stack processor they run more efficiently. So in 16K transistors, 4000 gates,
the F21 at 500 Mhz performed about the same as a 500Mhz 486 with JPEG compress and decompress.
With the parallel core design instead of a common bus or network between the processors there would only be 4 connections into and out of each processor. These would be 4 registers that are shared with it's 4 neighboring processors that are laid out in a grid. So each chip would have a north, south, east and west register.

Data would be processed in whats called a systolic array, where each core would pick up some data, perform operations on it and pass it along to the next core.

The chips with a 7x7 grid of processors would expose the 28(4x7) bus lines off the edge processors, so that these could be tiled into a much larger grid of processors.

Each chip could perform around 117 Billion instructions per second at 1 Watt of power.

Unfortunately I was unable to raise money, partly because I couldn't' get any commitment from Chuck.

below is some links and other misc information on this project. Sorry it's not better organized.
This was my project.

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http://www.enumera.com/chip/
http://www.enumera.com/doc/Enumeradraft061003.htm
http://www.enumera.com/doc/analysis_of_Music_Copyright.html
http://www.enumera.com/doc/emtalk.ppt

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This was Jeff foxes independent web site, he work on the F21 with Chuck.

http://www.ultratechnology.com/ml0.htm

http://www.ultratechnology.com/f21.html#f21
http://www.ultratechnology.com/store.htm#stamp

http://www.ultratechnology.com/cowboys.html#cm

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http://www.colorforth.com/ 25x Multicomputer Chip

Chucks site. 25x has been pulled down, but it's accessible on archive.org.
http://web.archive.org/web/*/www.colorfo