On Monday April 25 2011 15:34:55 Anders Logg wrote: > On Mon, Apr 25, 2011 at 03:28:30PM -0700, Johan Hake wrote: > > On Monday April 25 2011 15:19:20 Anders Logg wrote: > > > On Mon, Apr 25, 2011 at 03:14:45PM -0700, Johan Hake wrote: > > > > On Monday April 25 2011 15:04:43 Anders Logg wrote: > > > > > On Mon, Apr 25, 2011 at 10:56:25PM +0100, Garth N. Wells wrote: > > > > > > On 25/04/11 22:48, Anders Logg wrote: > > > > > > > On Mon, Apr 25, 2011 at 10:41:58PM +0100, Garth N. Wells wrote: > > > > > > >> On 25/04/11 22:33, Anders Logg wrote: > > > > > > >>> On Mon, Apr 25, 2011 at 10:26:18PM +0100, 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. > > > > > > >>> > > > > > > >>> The point would be that one could check that "hash" of the > > > > > > >>> form (some unique string) instead of computing the signature > > > > > > >>> which involves preprocessing the form. > > > > > > >> > > > > > > >> How would the hash be computed? To check if the mesh has > > > > > > >> changed, my limited understanding is that the entire object > > > > > > >> would have to be serialised, and then a hash computed. How > > > > > > >> expensive is that? > > > > > > >> > > > > > > >> The issue that I ran into was not related to signatures. It > > > > > > >> was related to the non-UFL data that is attached to > > > > > > >> arguments. > > > > > > > > > > > > > > The hash would be unique to each form. It could just be a > > > > > > > counter value and the counter would be increased inside > > > > > > > Instant for each object it gets as input. > > > > > > > > > > > > But how does Instant know if a form is new? I also don't see why > > > > > > Instant should need to know if the mesh associated with a form > > > > > > has changed, but is for the rest the same. Wouldn't Instant need > > > > > > to be DOLFIN-aware? > > > > > > > > > > The hash() function would play the same role as the id() function > > > > > before with the difference that we can't get the same id for a new > > > > > form as for an old form that's gone out of scope. > > > > > > > > > > Instant should not need to know anything it just does this: > > > > > check if object has a set_hash() function > > > > > if so, calls hash() to get the hash value > > > > > > > > > > checks the cache for that hash value > > > > > > > > > > if not, assign unique value by calling set_hash on the object > > > > > > > > > > We would need to make sure from the DOLFIN side that when we change > > > > > a Form, we also change the hash value (for example by setting it > > > > > to None) which would trigger the Instant disk cache. > > > > > > > > Sounds complicated... > > > > > > I think it sounds very easy. Everything we need is there: Instant > > > already has memory and disk cache. We just need to provide the proper > > > input. > > > > The set and get hash introduce another level of complexity. > > > > > > Now the preprocessed form is stored in the original form. This will > > > > never change. Whenever a form does not go out of scope the > > > > preprocessed form will live. > > > > > > > > Also Martin made it impossible to change a form without returning a > > > > new instance. This prevents any changing of the original form while > > > > keeping a preprocesses form attached to it. > > > > > > > > If a form has a preprocessed form that will be used for code > > > > generation. The preprocessed form will be used in instants memory > > > > cache. The preprocessed form has nothing to do the any DOLFIN > > > > objects that comes with the original form, such as mesh, expressions > > > > and such. > > > > > > > > Anything I have missed? > > > > > > What about the __hash__ function in jitobject.py? It still calls > > > id(). Isn't that a problem? > > > > No. The __hash__ is only used to retreive the memory cached compiled > > module in instant. This so we can retreive the compiled form. The > > form_data including all DOLFIN dependent data are stored in form_data > > which is just retrieved from the preprocessed form. > > Why is this not problematic if a new form is created which happens to > get the same id as an old destroyed form? I thought that was the > original issue.
Good point. The hash is only used to retreive the compiled module from instant memory cache, right? Then I think we can safely base the hash on the signature. Johan > Anders (offline until tomorrow) > > > A user can change this, but it seems that form_data is correctly updated > > with the new mesh. > > > > Btw: We could probably store the compiled form also in form_data. We > > could then avoid going through instant memory cache :) > > > > Johan _______________________________________________ Mailing list: https://launchpad.net/~ffc Post to : ffc@lists.launchpad.net Unsubscribe : https://launchpad.net/~ffc More help : https://help.launchpad.net/ListHelp
