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). > > > > -- > > 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
