Re: [Caml-list] Unboxing: how to do it best?

[Eray Ozkural <examachine@gmail.com>]

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Except that ocaml is hardly a slow scripting language, on many levels it's
directly comparable to C++ code. In my opinion, ocaml should be usable all
the way down to the kernel code. For many complex algorithms and data
structures, using C++ with all the zero-overhead level-headed
template-bloated pages-long low-level intricate imperative code you'll get a
very small constant factor improvement. For an actual non-trivial search
code I got only twice the speed of the ocaml code, even though I used
vectors instead of lists throughout. Not worth the effort at all. I wouldn't
even attempt it if I hadn't had to port the code to C++.

Thanks for the references by the way, I am actually interested in this. I'm
thinking of its extensions (i.e. distributed memory architectures, shared
memory cannot scale anyway).

Best,

On Sat, Jan 15, 2011 at 2:41 PM, bluestorm <bluestorm.dylc@gmail.com> wrote:

> I don't think it is easily possible inside Caml, as the data representation
> is tightly bound to the runtime system, and it would be very delicate to
> change it.
>
> If you are interested in the relevant litterature, you may want to see for
> example the bibliography on "Unboxing data representations" of
>   http://pauillac.inria.fr/~xleroy/talks/references-pldi98.html
> In particular, you may be interested in the Peyton-Jones and Launchbury
> paper, as they implemented their ideas into the GHC Haskell compiler which
> support some unboxed types.
>
> If you want to optimize the kernel of an existing OCaml program with
> unboxed manipulations, I think your best bet would be to switch to a
> lower-level language for your kernel. This is very common in scripting
> languages where you generally implement the -- hopefully tiny --
> performance-sensitive parts of your program in C. You still reap the
> benefits of OCaml abstractions for the larger, less performance-sensitive
> part of your program.
>
>
> On Sat, Jan 15, 2011 at 1:02 PM, Eray Ozkural <examachine@gmail.com>wrote:
>
>> It's obvious that avoiding pointer chasing, improving locality and
>> reducing storage will in some cases improve performance considerably. I've
>> found many discussions about unboxing, but I haven't seen any solutions that
>> would satisfy high-performance-computing programmers, who would probably
>> like to have better (i.e. fine-grained) control over memory layout (unboxing
>> double arrays isn't enough). In C++ this is trivial, because C++ is just an
>> abstraction of assembly code. To cut it short,  could not we have basically
>> the same affordances of C++ in ocaml by annotating type definitions to
>> indicate where unboxing would be forced? Such annotations aren't a new idea
>> in programming languages, specifically HPF was based largely on parallel
>> storage annotations.
>>
>> Regards,
>>
>> --
>> Eray Ozkural, PhD candidate.  Comp. Sci. Dept., Bilkent University, Ankara
>>
>>
>>
>


-- 
Eray Ozkural, PhD candidate.  Comp. Sci. Dept., Bilkent University, Ankara
http://groups.yahoo.com/group/ai-philosophy
http://myspace.com/arizanesil http://myspace.com/malfunct

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