On Monday April 25 2011 14:44:23 Garth N. Wells wrote: > On 25/04/11 22:29, Johan Hake wrote: > > I am working on a simple solution, where we store everything in the > > original ufl form. > > > > I might have something soon. > > OK. > > I played around with something like this, but had some issues when the > form changes (i.e. a += . . . ) after being preprocessed.
Oups! I guess my "fix" wont get this either... Maybe we need to destroy the form_data object whenever += ... are called? Johan > Garth > > > 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). > >>> > >>> -- > >>> Anders > >>> > >>> _______________________________________________ > >>> Mailing list: https://launchpad.net/~ffc > >>> Post to : ffc@lists.launchpad.net > >>> Unsubscribe : https://launchpad.net/~ffc > >>> More help : https://help.launchpad.net/ListHelp > >> > >> _______________________________________________ > >> Mailing list: https://launchpad.net/~ufl > >> Post to : u...@lists.launchpad.net > >> Unsubscribe : https://launchpad.net/~ufl > >> More help : https://help.launchpad.net/ListHelp _______________________________________________ Mailing list: https://launchpad.net/~ffc Post to : ffc@lists.launchpad.net Unsubscribe : https://launchpad.net/~ffc More help : https://help.launchpad.net/ListHelp
