[Numpy-discussion] Objected-oriented SIMD API for Numpy

Robert Kern robert.kern@gmail....
Thu Oct 22 10:51:14 CDT 2009


On Thu, Oct 22, 2009 at 02:35, Sturla Molden <sturla@molden.no> wrote:
> Robert Kern skrev:
>> No, I think you're right. Using "SIMD" to refer to numpy-like
>> operations is an abuse of the term not supported by any outside
>> community that I am aware of. Everyone else uses "SIMD" to describe
>> hardware instructions, not the application of a single syntactical
>> element of a high level language to a non-trivial data structure
>> containing lots of atomic data elements.
>>
> Then you should pick up a book on parallel computing.

I would be delighted to see a reference to one that refers to a high
level language's API as SIMD. Please point one out to me. It's
certainly not any of the ones I have available to me.

> It is common to differentiate between four classes of computers: SISD,
> MISD, SIMD, and MIMD machines.
>
> A SISD system is the classical von Neuman machine. A MISD system is a
> pipelined von Neuman machine, for example the x86 processor.
>
> A SIMD system is one that has one CPU dedicated to control, and a large
> collection of subordinate ALUs for computation. Each ALU has a small
> amount of private memory. The IBM Cell processor is the typical SIMD
> machine.
>
> A special class of SIMD machines are the so-called "vector machines", of
> which the most famous is the Cray C90. The MMX and SSE instructions in
> Intel Pentium processors are an example of vector instructions. Some
> computer scientists regard vector machines a subtype of MISD systems,
> orthogonal to piplines, because there are no subordinate ALUs with
> private memory.
>
> MIMD systems multiple independent CPUs. MIMD systems comes in two
> categories: shared-memory processors (SMP) and distributed-memory
> machines (also called cluster computers). The dual- and quad-core x86
> processors are shared-memory MIMD machines.
>
> Many people associate the word SIMD with SSE due to Intel marketing. But
> to the extent that vector machines are MISD orthogonal to piplined von
> Neuman machines, SSE cannot be called SIMD.

That's a fair point, but unrelated to whether or not numpy can be
labeled SIMD. These all refer to hardware.

> NumPy is a software simulated vector machine, usually executed on MISD
> hardware. To the extent that vector machines (such as SSE and C90) are
> SIMD, we must call NumPy an object-oriented SIMD library.

numpy does not "simulate" anything. It is an object-oriented library.
If numpy could be said to "simulate" a vector machine, than just about
any object-oriented library that overloads operators could. It creates
a false equivalence between numpy and software that actually does
simulate hardware.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco


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