Re: Lush2 performance

I have reintegrated the code that spawns a child
process for the garbage collection. You need to
activate it explicitly at configure time,

./configure --with-snapshot-gc

If you do not have an issue with lush's responsiveness
then there is no reason to activate it.

I plan to maintain the garbage collector as an
independent project (libcmm.sf.net). Lush should link to
the library, starting in some future release, and take
advantage of improvements to the collector in this way.

A few more comments on the intended use of this
feature. This is, strictly speaking, not a solution that
uses multi-threading. It uses the fork() system call,
which is not available on Windows, for instance. It is
also a more heavy-weight operation than starting a thread.
For actual realtime applications you would need a realtime
OS and response-time guarantees for system calls.
I suppose this will work well enough in practice for quasi
realtime applications like Yann's robots. But be aware
that fork() may fail under heavy system load!
You would then see a message from the MM module,

mm(collect): could not spawn child for GC: Cannot allocate memory
mm(collect): trying synchronous collect

Ralf



On Sun, 15 Mar 2009, Yann LeCun wrote:

> Unfortunately (as you probably suspected), shutting off gc doesn't
> solve the problem.
>
> If a robot runs a sensor-reading/actuator-controlling loop, it will
> eventually run out of memory and probably crash unless the gc is
> called periodically. While gc runs, the robot runs blinds (or the
> game, video, or music stops in a multimedia app).
>
> One possibility is to systematically call the gc at the end of the loop,
> but the question is: how long does the gc takes to complete, even if
> little a small amount of memory was allocated since the last call?
>
> On the current SVN version of lush2, a simple call to (gc) on a
> "blank" interpreter (right after startup) takes about 15ms on my
> Core2Duo laptop. That makes the option of calling (gc) all the time
> totally impractical.
>
> If lush2 is to be used for applications where a predictable response
> time is required, which includes real-time vision and signal
> processing, robotics, games, video and multimedia, it seems to me that
> a separate gc thread is the only viable solution.
>
> That's precisely why Java has a separate thread for gc.
>
> These applications are very important to many Lush users.
>
>  -- Yann
>
>
> On Sunday 15 March 2009, Ralf Juengling wrote:
>> Not sure if it solves the problem, but I added a new
>> form 'with-nogc' which temporarily blocks garbage
>> collections. Should work when the number of allocations
>> in the loop is within reasonable limits.
>>
>> You can do a similar thing in C (see the implementation
>> of with-nogc in toplevel.c).
>>
>> Ralf
>>
>> On Wed, 11 Mar 2009, Yann LeCun wrote:
>>> One problem with a single thread implementation of
>>> course is that it pretty much precludes the use
>>> of Lush 2.0 for any semi-real-time application
>>> like robotics or games. For these applications
>>> you want a repeatable run time for a loop, and
>>> can't afford to have the system sit around and do
>>> garbage collection once in a while.
>>>
>>> So, maintaining the option to spawn a separate
>>> thread for GC might be a good idea.
>>>
>>>  -- Yann
>>
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