OCaml is broken

OCaml is broken

[Erik Rigtorp]

Hi!

I've been using Erlang and C++ to build a soft real-time system. As
the project has evolved we've needed to write more and more of the
code in C++ in order to achieve our latency requirements. But C++ is
not as performant as you might think until you start to write your own
allocators and cache aligning mallocs and datastructures. I've never
liked C++ so I decided to try OCaml and built a simple 100 line
program to build order books for Nasdaq. Turns out OCaml has really
competitive performance while being a really nice language.

However OCaml is broken! It does not provide any support for multicore
architectures, which by now is considered a bug! It doesn't even allow
me to load multiple runtimes into one C program.

Please fix OCaml! The first step would be to support multiple runtimes
running in the same process communicating using message queues.

Erik Rigtop

Re: [Caml-list] OCaml is broken

[Stéphane Glondu]

Erik Rigtorp a écrit :
> However OCaml is broken! It does not provide any support for multicore
> architectures, which by now is considered a bug! [...]

You might be interested by OCaml4Multicore:

  http://www.algo-prog.info/ocmc/web/

It's still experimental, but its authors would love to have feedback.


Best regards,

-- 
Stéphane

Re: OCaml is broken

[Sylvain Le Gall]

On 19-12-2009, Erik Rigtorp <erik@rigtorp.com> wrote:
>
> Please fix OCaml! The first step would be to support multiple runtimes
> running in the same process communicating using message queues.
>

You should take a look at:
http://jocaml.inria.fr/

Regards,
Sylvain Le Gall

Re: [Caml-list] OCaml is broken

[Thomas Fischbacher]

Erik Rigtorp wrote:

> However OCaml is broken! It does not provide any support for multicore
> architectures, which by now is considered a bug! It doesn't even allow
> me to load multiple runtimes into one C program.

My washing machine is broken. I cannot bake Pizza with it.

-- 
best regards,
Thomas Fischbacher
t.fischbacher@soton.ac.uk

Re: [Caml-list] OCaml is broken

[Gerd Stolpmann]

Am Samstag, den 19.12.2009, 10:30 +0100 schrieb Erik Rigtorp:
> Hi!
> 
> I've been using Erlang and C++ to build a soft real-time system. As
> the project has evolved we've needed to write more and more of the
> code in C++ in order to achieve our latency requirements. But C++ is
> not as performant as you might think until you start to write your own
> allocators and cache aligning mallocs and datastructures. I've never
> liked C++ so I decided to try OCaml and built a simple 100 line
> program to build order books for Nasdaq. Turns out OCaml has really
> competitive performance while being a really nice language.
> 
> However OCaml is broken! It does not provide any support for multicore
> architectures, which by now is considered a bug! It doesn't even allow
> me to load multiple runtimes into one C program.
> 
> Please fix OCaml! The first step would be to support multiple runtimes
> running in the same process communicating using message queues.

As you mention order books and soft-realtime, I guess your main concern
are minimized latencies. Well, you need then a style of parallelism that
focuses on a certain processing path for a single data item, and where
the latency is minimized by using several cores. I think ocaml is
unsuited for this type of task, but please don't call ocaml "broken"
because of this. Other types of parallelism can be well supported,
especially when you can accept multi-processing, and when you focus on
larger processing paths and partitioned data sets.

Gerd
-- 
------------------------------------------------------------
Gerd Stolpmann, Bad Nauheimer Str.3, 64289 Darmstadt,Germany 
gerd@gerd-stolpmann.de          http://www.gerd-stolpmann.de
Phone: +49-6151-153855                  Fax: +49-6151-997714
------------------------------------------------------------

Re: [Caml-list] OCaml is broken

[Erik Rigtorp]

On Sun, Dec 20, 2009 at 17:18, Gerd Stolpmann <gerd@gerd-stolpmann.de> wrote:
> As you mention order books and soft-realtime, I guess your main concern
> are minimized latencies. Well, you need then a style of parallelism that
> focuses on a certain processing path for a single data item, and where
> the latency is minimized by using several cores. I think ocaml is
> unsuited for this type of task, but please don't call ocaml "broken"

It is actually perfectly suitable for this, as long as you can run
multiple runtimes and share data via low latency message passing. This
is kind of how Erlang does it, with a separate heap for each
lightweight thread (called process in Erlang).

> because of this. Other types of parallelism can be well supported,
> especially when you can accept multi-processing, and when you focus on
> larger processing paths and partitioned data sets.

I agree, but fork() and pipe() has problems.

1. Latency is high ~10µs when tuned on Solaris, substantially higher
>100µs on Linux.
2. Runtimes don't share memory so data has to be copied. This is fine
for small datasets or streaming data, like passing order book updates
around.

Even if I want to process a dataset and partition it and sends the
work to multiple processes there is no framework in OCaml for me to
use.

Erik

Re: OCaml is broken

[Sylvain Le Gall]

On 21-12-2009, Erik Rigtorp <erik@rigtorp.com> wrote:
> On Sun, Dec 20, 2009 at 17:18, Gerd Stolpmann <gerd@gerd-stolpmann.de> wrote:
>
> Even if I want to process a dataset and partition it and sends the
> work to multiple processes there is no framework in OCaml for me to
> use.
>

There are many frameworks at hand, just search for it:
- ocamlp3l
- jocaml
- RPC with ocamlnet
- cothreads
- Ancient
- OCamlMPI

They maybe not look like exactly what you want, but they are close
enough to do what you want.

FYI, I have created a commercial application for sorting/processing big
files using OCaml. It runs using multi-processes as fast as other
commercial programs that do the same thing. In particular, it runs
faster than another well-known program written in C, using threads on
Windows and on Linux. 

Regards,
Sylvain Le Gall

Re: [Caml-list] Re: OCaml is broken

[Richard Jones]

On Mon, Dec 21, 2009 at 09:21:09PM +0000, Sylvain Le Gall wrote:
> On 21-12-2009, Erik Rigtorp <erik@rigtorp.com> wrote:
> > On Sun, Dec 20, 2009 at 17:18, Gerd Stolpmann <gerd@gerd-stolpmann.de> wrote:
> >
> > Even if I want to process a dataset and partition it and sends the
> > work to multiple processes there is no framework in OCaml for me to
> > use.
> >
> 
> There are many frameworks at hand, just search for it:
> - ocamlp3l
> - jocaml
> - RPC with ocamlnet
> - cothreads
> - Ancient
> - OCamlMPI

Since the OP is interested in latencies, he may also want to look at
the tools lower down the stack for pinning processes and interrupts to
physical CPUs (eg. Tuna http://userweb.kernel.org/~acme/tuna/), and
also at RT kernels.

Red Hat is funding a large amount of research in this area under the
general brand name of MRG (Messaging, Real time and Grid computing):

http://www.redhat.com/mrg/

and we're doing this in partnership with some very large banks.

None of that is really specific to OCaml.  In fact the banks tend to
use Java(!)

Rich.

-- 
Richard Jones
Red Hat

Re: [Caml-list] OCaml is broken

[Florian Weimer]

* Erik Rigtorp:

> However OCaml is broken! It does not provide any support for multicore
> architectures, which by now is considered a bug!

The run-time library is sufficiently small so that you can run
multiple processes in parallel.  They will even share the code and
constant data.

> It doesn't even allow me to load multiple runtimes into one C
> program.

That should perhaps be fixed, yes.