Re: [Caml-list] OC4MC : OCaml for Multicore architectures

[Philippe Wang <philippe.wang.lists@gmail.com>]

On Thu, Sep 24, 2009 at 3:47 AM, Jon Harrop <jon@ffconsultancy.com> wrote:
> Following your advice, it seems to work perfectly now:

:-)

> Wow! 2.6x faster on 2 cores is good. ;-)

your machine is more generous than ours (which is Intel, not AMD) :-)

> That's a really fantastic piece of work. I'll do my best to study it and write
> literature about it. May I ask, can you give a rough overview of the design?
> For example, is there a separate nursery per thread so each thread can
> allocate a certain amount before incurring a global pause? Do you have any
> ideas for libraries built on top of this, such as a task parallel library
> using work-stealing deques?

A few words on the GC's design (that uses stop&copy algorithm several times) :

Heaps :
- a set of pages are used to give threads the possibility to allocate
memory without interfering with other threads, such as there is no
mutex locking at local memory allocation. Each thread borns with an
empty page, when it's full, the thread takes another one.
- a big heap is shared between all, there is a mutex over it to
prevent parallel memory allocation into this one.

Collection :
- when there are no pages left, a collection stops-the-world and
copies living values (of the pages) to the shared heap
- when the shared heap is full, a collection stops-the-world and
copies all living values (pages+shared heap) to a new shared heap
(which can be grow if need be)

Special operations :
- if there is a blocking operation (e.g. mutex lock or I/O operation),
the mechanism is roughly the same as original INRIA OCaml's : it tells
the GC that there is no need to stop it when stopping the world.
- if there is a thread with no allocation and no blocking operation,
the behaviur is the same as INRIA OCaml.


The number of pages, the size of a page, and the size of the shared
heap can be changed before running a program by setting some
environment variables (cf. last lines README file included in the
distribution package).



-- 
Philippe Wang
   mail@philippewang.info