dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Monday February 21 2011 12:31:18 Garth N. Wells wrote:
> On 21/02/11 18:00, Johan Hake wrote:
> > On Monday February 21 2011 08:18:18 Garth N. Wells wrote:
> >> On 17/02/11 21:28, Johan Hake wrote:
> >>> Hello!
> >>> 
> >>> I have a not so large 3D mesh of some 50K vertices, generated from some
> >>> geometry (not UnitCube).
> >>> 
> >>> When I set
> >>> 
> >>>   parameters.num_threads = 2
> >>> 
> >>> and try to assemble I just get:
> >>>   Coloring mesh.
> >>> 
> >>> and then it seems it wont find a solution... I had to break it because
> >>> it nearly hang the computer for some 5 min.
> >>> 
> >>> Have anyone experience the same? Is there any way to controll the
> >>> coloring?
> >> 
> >> It's had minimal testing, so issues can be expected. Can you post your
> >> solver? 50k vertices is not very big, so I would expect it to be pretty
> >> fast.
> > 
> > Yes I would expect that too. I have used the coloring on other meshes
> > with success.
> > 
> > The mesh can be downloaded from here:
> >   <http://folk.uio.no/hake/trouble.xml.gz>
> > 
> > To reproduce the trouble just run:
> >   from dolfin import *
> >   mesh = Mesh('trouble.xml.gz')
> >   V = FunctionSpace(mesh, "CG", 1)
> >   assemble(Function(V)*dx)
> >   parameters.num_threads = 2
> >   assemble(Function(V)*dx)
> > 
> > The mesh has two distinct domains, but that shouldnto be causing the
> > trouble, as other I have successfully colored other such meshes. I guess
> > it can be the particular mesh that causes coloring to stall. It is
> > generated using tetgen.
> 
> I don't think that I've tested multi-threaded assembly for functionals.
> 
> When we get around to implementing it, assembling functionals shouldn't
> require colouring. It should just involve OpenMP parallelising the
> assembly loop, and then each thread adds its contribution to the result
> once it's processed its bunch of cells (while avoiding a race condition).

I just used a Functional so I could stick with a shorter example ;)

The above code works fine with another mesh. Changing the form to a linear or 
bilinear form triggers the same coloring (right?), which stalls on this 
particular mesh.

Johan

> Garth
> 
> > At the end of the day I have to wait untill we support subdomains in the
> > OpenMPAssembler as I am heavily using these...
> > 
> > Johan
> > 
> >> Garth
> >> 
> >>> Johan
> >>> 
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