On 26 April 2011 11:09, Garth N. Wells <gn...@cam.ac.uk> wrote:
>
>
> On 26/04/11 09:56, Garth N. Wells wrote:
> >
> >
> > On 26/04/11 09:03, Martin Sandve Alnæs wrote:
> >> See other mail. I don't see that it solves anything, it doesn't seem
> >> related to anything I've read about in this thread, and it has a
> >> potential backside in hindering the garbage collector in Python. I may
> >> be wrong, but nobody has answered my other questions about this thread
> yet.
> >>
> >
> > As a precursor, the primary problem has nothing to do with Instant disk
> > cache, etc. The Instant discussion is just confusing the original point.
> >
> > In summary, is it helpful if DOLFIN can avoid calling ufl.preprocess
> > every time a dolfin.Form object is created. DOLFIN relies on
> > preprocessing to extract the form Arguments, from which the mesh is
> > extracted (via form_data().original_arguments, and since DOLFIN uses
> > 'Arguments' that are subclasses of UFL and DOLFIN objects).
> >
> > The solution that Johan has implemented is to have FFC attach the
> > form_data to a form. If a form has form_data attached, then we know that
> > it has already been preprocessed. Martin won't like this because it's
> > changing the form object.
> >
> > It may be enough if UFL would provide a function to return a list of
> > form Arguments, if this is fast. Something like
> >
> > def extract_original_arguments(form):
> >
> > # Replace arguments and coefficients with new renumbered objects
> > arguments, coefficients = extract_arguments_and_coefficients(form)
> > replace_map, arguments, coefficients \
> > = build_argument_replace_map(arguments, coefficients)
> > form = replace(form, replace_map)
> >
> > # Build mapping to original arguments and coefficients, which is
> > # useful if the original arguments have data attached to them
> > inv_replace_map = {}
> > for v, w in replace_map.iteritems():
> > inv_replace_map[w] = v
> > original_arguments = [inv_replace_map[v] for v in arguments]
> >
> > return original_arguments
> >
>
> As addition, I think that we're letting DOLFIN specific issues creep
> into FFC and UFL. It would be simple if FFC simply did
>
> if form.form_data() is not None:
> preprocessed_form = form
> else:
> preprocessed_form = preprocess(form, common_cell=common_cell)
>
>
Is this ufl.preprocess or ffc.preprocess?
> and DOLFIN is made responsible for preprocessing a form (or not
> preprocessing) before sending it to the FFC JIT compiler, particularly
> since deciding to preprocess or not can depend on what DOLFIN-specific
> data (e.g. meshes) has been attached to the form.
Here I'm lost. Why is preprocessing dependent on dolfin anything?
What kind of preprocessing are we talking about here?
Martin
> Garth
>
>
>
>
>
> > Garth
> >
> >
> >> Martin
> >>
> >> On 26 April 2011 09:20, Garth N. Wells <gn...@cam.ac.uk
> >> <mailto:gn...@cam.ac.uk>> wrote:
> >>
> >> Martin: Any problem if we apply this patch to UFL?
> >>
> >> Garth
> >>
> >> On 25/04/11 22:50, Johan Hake wrote:
> >> > This should be fixed now.
> >> >
> >> > I do not see why we introduced the memory cache when this solution
> >> was laying
> >> > right in front our eyes...
> >> >
> >> > Anyhow. Here is a patch for ufl to avoid circular dependency
> between a
> >> > preprocessed form and the form_data.
> >> >
> >> > Johan
> >> >
> >> > On Monday April 25 2011 14:34:00 Anders Logg wrote:
> >> >> Simple sounds good.
> >> >>
> >> >> --
> >> >> Anders
> >> >>
> >> >> On Mon, Apr 25, 2011 at 02:29:50PM -0700, Johan Hake wrote:
> >> >>> I am working on a simple solution, where we store everything in
> the
> >> >>> original ufl form.
> >> >>>
> >> >>> I might have something soon.
> >> >>>
> >> >>> Johan
> >> >>>
> >> >>> On Monday April 25 2011 14:26:18 Garth N. Wells wrote:
> >> >>>> On 25/04/11 22:08, Anders Logg wrote:
> >> >>>>> On Mon, Apr 25, 2011 at 07:40:21PM -0000, Garth Wells wrote:
> >> >>>>>> On 25/04/11 20:00, Johan Hake wrote:
> >> >>>>>>> On Monday April 25 2011 11:26:36 Garth Wells wrote:
> >> >>>>>>>> On 25/04/11 18:51, Anders Logg wrote:
> >> >>>>>>>>> On Mon, Apr 25, 2011 at 05:11:41PM -0000, Garth Wells
> wrote:
> >> >>>>>>>>>> On 25/04/11 17:53, Johan Hake wrote:
> >> >>>>>>>>>>> On Monday April 25 2011 08:59:18 Garth Wells wrote:
> >> >>>>>>>>>>>> On 25/04/11 16:47, Johan Hake wrote:
> >> >>>>>>>>>>>>> Commenting out the cache is really not a fix. The
> >> problem is
> >> >>>>>>>>>>>>> within dolfin. Isn't there another way to deal with
> this?
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>> It is a fix if the cache isn't needed.
> >> >>>>>>>>>>>
> >> >>>>>>>>>>> Sure.
> >> >>>>>>>>>>>
> >> >>>>>>>>>>>>> First: How much penalty are there with a disabled
> memory
> >> >>>>>>>>>>>>> cache. Maybe the problem isn't that bad?
> >> >>>>>>>>>>>>
> >> >>>>>>>>>>>> I don't get the point of this cache. The way it is now,
> >> a form
> >> >>>>>>>>>>>> is only preprocessed if it hasn't already been
> >> preprocessed,
> >> >>>>>>>>>>>> which seems ok to me. The old code tried to avoid some
> >> >>>>>>>>>>>> preprocessing, but it was highly dubious and I doubt
> >> that it
> >> >>>>>>>>>>>> was effective.
> >> >>>>>>>>>>>
> >> >>>>>>>>>>> I think the preprocessing stage actually do take some
> time.
> >> >>>>>>>>>>> AFAIK the preproces stage essentially do two things. It
> >> >>>>>>>>>>> creates a canonical version of the Form so two Forms
> >> that are
> >> >>>>>>>>>>> the same, but constructed at different times are beeing
> >> >>>>>>>>>>> treated equal wrt form generation. Then are DOLFIN
> specific
> >> >>>>>>>>>>> guys extracted. I am not sure what takes the most time.
> We
> >> >>>>>>>>>>> should probably profiel it... But if it is the latter we
> >> could
> >> >>>>>>>>>>> consider putting another cache in place which is more
> robust
> >> >>>>>>>>>>> wrt changing DOLFIN objects.
> >> >>>>>>>>>>
> >> >>>>>>>>>> It should be easy to avoid the overhead of preprocessing
> by
> >> >>>>>>>>>> keeping the object in scope. If the object changes, the
> only
> >> >>>>>>>>>> robust way to make sure that the form is the same as one
> >> in the
> >> >>>>>>>>>> cache is to compare all the data. This requires
> preprocessing
> >> >>>>>>>>>> the form, which then defeats the purpose of a cache. It
> >> may be
> >> >>>>>>>>>> possible to add a lightweight preprocess to UFL, but I
> don't
> >> >>>>>>>>>> think that it's worth the effort or extra complication.
> >> >>>>>>>
> >> >>>>>>> I think a light weight version might be the way to go. This
> >> is then
> >> >>>>>>> stored in memory cache. If we are able to strip such a form
> >> for all
> >> >>>>>>> DOLFIN specific things we would also prevent huge memory
> >> leaks with
> >> >>>>>>> mesh beeing kept.
> >> >>>>>>>
> >> >>>>>>> Then we always grab DOLFIN specific data from the passed
> form
> >> >>>>>>> instead of grabbing from the cache. Not sure how easy this
> >> will be
> >> >>>>>>> to implement, but I think we need to explore it, as the
> DOLFIN
> >> >>>>>>> specific part of the form really has nothing to do with the
> >> >>>>>>> generated Form.
> >> >>>>>>>
> >> >>>>>>> Martin:
> >> >>>>>>> Why is it important to have the _count in the repr of the
> >> form? I
> >> >>>>>>> guess that is used in ufl algorithms? Would it be possible
> to
> >> >>>>>>> include a second repr function, which did not include the
> count?
> >> >>>>>>> This would then be used when the signature is checked for.
> We
> >> >>>>>>> could then use that repr to generate a form which is stored
> >> in the
> >> >>>>>>> memory cache. This would then be tripped for any DOLFIN
> specific
> >> >>>>>>> objects. This should work as the _count attribute has
> nothing to
> >> >>>>>>> do with what code gets generated, but it is essential for
> >> internal
> >> >>>>>>> UFL algorithms, right?
> >> >>>>>>>
> >> >>>>>>>>> I'm not very happy with this change.
> >> >>>>>>>>
> >> >>>>>>>> The bright side is that slow and correct is a better
> starting
> >> >>>>>>>> point than fast but wrong ;).
> >> >>>>>>>>
> >> >>>>>>>> An easy fix is to attach the preprocessed form to a Form
> >> object.
> >> >>>>>>>> This would work robustly if we can make forms immutable
> once
> >> >>>>>>>> they've been compiled. Is it possible to make a Python
> object
> >> >>>>>>>> immutable?
> >> >>>>>>>
> >> >>>>>>> We can probably overload all setattribtue methods which
> >> prohibits a
> >> >>>>>>> user to write to these but it might not be possible to
> >> prohibit a
> >> >>>>>>> user to change attributes on instances owned by the Form. I
> >> guess
> >> >>>>>>> this is similare to the difficulties of preserving constness
> in
> >> >>>>>>> C++, but I think it is even harder in Python.
> >> >>>>>>
> >> >>>>>> What if we have the FFC jit compiler return the preprocessed
> >> form,
> >> >>>>>> and inside dolfin.Form simply do
> >> >>>>>>
> >> >>>>>> class Form(cpp.Form):
> >> >>>>>> def __init__(self, form, . . .. )
> >> >>>>>> ....
> >> >>>>>>
> >> >>>>>> (...., preprocessed_form) = jit(form, . . . . )
> >> >>>>>>
> >> >>>>>> form = preprocessed_form
> >> >>>>>>
> >> >>>>>> .....
> >> >>>>>>
> >> >>>>>> This way, form will have form_data, and the FFC jit function
> will
> >> >>>>>> know not to call ufl.preprocess.
> >> >>>>>
> >> >>>>> Here's another strange thing. In the JITObject class, we have
> two
> >> >>>>> functions: __hash__ and signature. As far as I understand, the
> >> first
> >> >>>>> is used to located objects (generated code/modules) in the
> Instant
> >> >>>>> in-memory cache, while the second is used for the on-disk
> cache.
> >> >>>>>
> >> >>>>> >From some simple tests I did now, it looks like the __hash__
> >> function
> >> >>>>>>
> >> >>>>> does not need to any significant speedup. The JIT benchmark
> >> runs just
> >> >>>>> as fast if I call signature from within __hash__.
> >> >>>>>
> >> >>>>> Furthermore, the __hash__ function must also be broken since
> it
> >> >>>>> relies on calling id on the form.
> >> >>>>>
> >> >>>>> Ideally, we should get Instant to handle the caching, both
> >> in-memory
> >> >>>>> and on-disk, by providing two functions __hash__ (fast, for
> >> in-memory
> >> >>>>> cache) and signature (slow, for on-disk cache).
> >> >>>>>
> >> >>>>> Since __hash__ cannot call id, it must be able to attach a
> unique
> >> >>>>> string to the form (perhaps based on an internal counter in
> FFC).
> >> >>>>> My suggestion would be to add this to UFL, something like
> set_hash
> >> >>>>> and hash (which would return None if set_hash has not been
> >> called).
> >> >>>>> If Martin does not like that, we should be able to handle it
> >> on the
> >> >>>>> DOLFIN side.
> >> >>>>>
> >> >>>>> So in conclusion: no in-memory cache in FFC (handled by
> >> Instant) and
> >> >>>>> FFC attaches a hash to incoming forms so that Instant may
> >> recognize
> >> >>>>> them later.
> >> >>>>
> >> >>>> The code that I disabled was caching preprocessed forms, so I
> >> don't see
> >> >>>> how this can be handled by Instant.
> >> >>>>
> >> >>>> Garth
> >> >>>>
> >> >>>>> Maybe even better: Instant checks whether an incoming object
> has a
> >> >>>>> set_hash function and if so calls it so it can recognize
> >> objects it
> >> >>>>> sees a second time.
> >> >>>>>
> >> >>>>> I'm moving this discussion to the mailing list(s).
> >> >>>>
> >> >>>> _______________________________________________
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> >>
> >
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